Shortly after the first cases of acquired immunodeficiency syndrome (AIDS) were recognized among civilians in 1981, early forms of the disease (AIDS-related complex and lymphadenopathy syndrome) were detected among active duty personnel. The causative virus (now called the human immunodeficiency virus, HIV) was first isolated from ill soldiers and their asymptomatic but nonetheless infected wives in 1984. These military studies provided the first proof that HIV could be transmitted through heterosexual intercourse. Nationwide blood bank testing for HIV began in June 1985. Shortly thereafter, in October 1985, the Department of Defense (DoD) began screening all civilian applicants for military service; those who tested positive for the virus were medically disqualified from service. Overall, 1 in 650 applicants was found to be infected, but prevalence rates in various geographic and demographic subpopulations varied from as low as 1 in 20,000 in the upper Midwest to 1 in 50 in northeastern urban centers. The HIV screening program was the first population-based screening program in the United States, and provided the first hard data that the epidemic had already spread silently throughout the country by the mid-1980s.
HIV screening of active duty military personnel began in 1986. Based largely on the recommendations of the Armed Forces Epidemiological Board, policies for HIV infection were established to be comparable to those for any other chronic medical condition. Infected military personnel were to remain on active duty, to lodge in military quarters, and to continue work in their duty assignment. Implemented at a time when fear of HIV contagion was widespread in the United States, these policies were farsighted and courageous. All DoD HIV-positive personnel were to be medically evaluated periodically, and those with advanced disease were honorably discharged with medical disability and benefits. HIV-infected personnel were restricted from overseas deployment, from health care jobs where potentially risky procedures were performed, and from sensitive Personal Reliability Program (e.g., nuclear missile) positions. In an effort to decrease HIV transmission, HIV-infected active duty personnel were counseled by their commanders that if they knowingly put others at risk of infection through sexual intercourse, they could be prosecuted through the military justice system. Overall, DoD policies were designed to reflect fair and rational public health principles.
Screening was originally undertaken annually for all active duty personnel, but this interval has gradually lengthened with a number of new service-specific regulations. For example, testing takes place every five years for all air force personnel, or for the following clinically indicated reasons: during pregnancy; on entry into a drug/alcohol rehabilitation program; on presenting at a STD (sexually-transmitted disease) clinic; on deployment overseas; on PCS (Permanent Change of Station) overseas. However, all personnel must be proven negative within six months of any overseas deployment.
The U.S. military HIV research program began in 1986, when Congress provided $40 million for this purpose. The U.S. Army Medical Research and Development Command, as the lead agency for infectious disease research, managed the tri-service program. Major accomplishments include the following firsts: definition of antibody test criteria for a diagnosis of HIV (criteria used worldwide today); evidence that HIV was becoming a serious problem among minorities; detection of transmission of drug-resistant HIV strains; tracking the global spread of genetic variants; vaccine therapy trials; and international preventive vaccine trials.
At the heart of the controversy over HIV/AIDS research is the question of its relevance to the military. HIV/AIDS has little or no direct impact on readiness or combat operations for U.S. forces. However, recent studies have shown very high HIV prevalences among some African (one in four) and Asian (one in ten) military populations. From a broader national security point of view, the global pandemic is a threat requiring maximal efforts by all capable U.S. agencies.
Rates for new infections have decreased; in 1995, the DoD's total of infections among active duty personnel was approximately 300. In 1996, an amendment to the department's authorization bill ruled that all HIV-infected personnel on active duty must be involuntarily separated, regardless of their fitness for duty or years of service; however, as of 1999, the policy was not to separate HIV-infected personnel who were physically fit. The impact of this legislation on the effectiveness of public health control of HIV within the military remains to be determined.
HIV
HIV, the human immunodeficiency virus, is the virus that causes AIDS, a debilitating and deadly disease of the human immune system. HIV is one of the world's most serious health problems: at the end of 2001, more than 40 million people worldwide were infected with HIV and living with the virus or AIDS. The World Health Organization estimates that about 20 million people have died from AIDS since the infection was first described in 1981. Nearly 500,000 of those deaths have occurred in the United States. Although there is no cure for the disease, therapies exist that reduce the symptoms of AIDS and can extend the life spans of HIV-infected individuals. Researchers are also pursuing protective vaccines, but a reliable vaccine might still require years to develop.
Hiv and Aids
HIV infects certain cells and tissues of the human immune system and takes them out of commission, rendering a person susceptible to a variety of infections and cancers. These infections are caused by so-called opportunistic agents, pathogens that take advantage of the compromised immune system but that would be unable to cause infection in people with a healthy immune system. Rare cancers such as Kaposi's sarcoma also take hold in HIV-infected individuals. The collection of diseases that arise because of HIV infection is called acquired immune deficiency syndrome, or AIDS. HIV is classified as a lentivirus ("lenti" means "slow") because the virus takes a long time to produce symptoms in an infected individual.
Hiv Life Cycle: Entering Cells
Like a typical virus, HIV infects a cell and appropriates the host's cellular components and machinery to make many copies of itself. The new viruses then break out of the cell and infect other cells. HIV stores its genetic information on an RNA molecule rather than a DNA chromosome. This is a distinguishing characteristic of retroviruses, which are viruses that must first convert their RNA genomes into DNA before they can reproduce.
Each HIV virion (viral particle) is a small sphere composed of several layers. The external layer is a membrane coat, or envelope, obtained from the host cell in which the particle was made. Underneath this membrane lies a shell made from proteins, called a nucleocapsid. Inside the protein shell are two copies of the virion's RNA genome and three kinds of proteins, which are used by the virion to establish itself once inside the cell that it infects.
Two proteins, called gp120 and gp41, enable the virion to recognize the type of cell to enter. These proteins project from the HIV membrane coat. Gp120 binds to two specific proteins found on the target cell's surface (these target-cell proteins are called receptors). The first receptor, CD4, is found on immune system cells known as CD4 T cells, and also sometimes on two cell types known as macrophages and dendritic cells. The immune system uses CD4 T cells in the initial step in making antibodies against infectious agents. After binding to CD4, the HIV protein called gp120 binds with a second cell membrane protein, commonly referred to as the co-receptor. The co-receptor can be one of many different proteins, depending on the cell type. The two most common are CXCR4, which is normally found on CD4 T cells, and CCR5, a receptor found on CD4 T cells as well as on certain macrophages and dendritic cells. In the absence of HIV, CXCR4 and CCR5 allow these immune system cells to respond to chemical signals, but when HIV infects the cells, the HIV commandeers their usage. In some cases, individuals have a mutation in their co-receptor that prevents HIV from entering their cells.
Once gp120 has bound to both the CD4 receptor and co-receptor, the gp41 protein fuses HIV's membrane envelope with the cellular membrane, injecting the virus into the target cell. Once in the cytoplasm, the viral protein shell opens up and releases the viral proteins—a reverse transcriptase, a viral integrase, and a protease—along with the viral RNA strands. The reverse transcriptase copies the RNA strands into DNA. The viral integrase then helps insert the DNA copies into the cell's chromosome. At this point, the virus is called a provirus, and the life cycle halts. The provirus may remain dormant in the cell's chromosome for months or years, waiting for the T cell to become activated by the immune system.
Hiv Life Cycle: Reproduction
When the immune system recruits T cells to fight an infection, the T cells start producing many proteins. Along with the normal cellular protein products, a T cell carrying an HIV provirus also produces HIV proteins. The first HIV proteins made are called Tat and Rev. Tat encourages the cellular machinery to copy HIV's proviral DNA into RNA molecules. These RNA molecules are then processed in the nucleus to become templates for several of the HIV proteins, some of whose functions are not well understood.
Rev, on the other hand, ushers the HIV's RNA molecules from the nucleus, where they are being reproduced, into the host cell's cytoplasm. Early in HIV reproduction, with only a few RNA molecules from which to make protein, a small quantity of Rev is made. Therefore, most of the RNA molecules remain in the nucleus long enough to get processed. As time passes, however, and Tat continues to instigate RNA production, more Rev is made. A higher amount of Rev protein increases the speed with which RNA molecules are ejected from the nucleus. These RNA molecules, which have undergone little or no processing, become templates to make different HIV proteins. The newer proteins are made in long chains that require trimming before they become functional. One of the proteins in the chain is the protease, the protein that trims. Other proteins include those that make up the protein shell, the reverse transcriptase, and integrase.
After the newly created proteins are processed to the right size, they form new virions by first assembling into a shell, then drawing in two unprocessed RNA molecules and filling up the remaining space with integrase, protease, and replicase. The new virions bud from the host-cell membrane, appropriating some of that membrane to form an outer coat in the process. The mature virus particles are now ready to infect other cells.
Hiv's Immune-System Impairment Mechanism
One of the most disastrous effects of HIV infection is the loss of the immune system's CD4 T cells. These cells are responsible for recognizing foreign invaders to a person's body and initiating antibody production to ward off the infection. Without them, people are susceptible to a variety of diseases. HIV destroys the T cells slowly, sometimes taking a decade to destroy a person's immunity. However, in all the time before an HIV-infected individual shows any symptoms, the virus has been reproducing rapidly. The lymph tissue, the resting place for CD4 T cells, macrophages, and dendritic cells, becomes increasingly full of HIV, and viral particles are also released into the bloodstream.
HIV's main target is the population of CD4 T cells within a host's body. HIV kills them in one of three ways. It kills them directly by reproducing within them, then breaking them upon exit; it kills them indirectly by causing the cells to "commit suicide" by inducing apoptosis; or it kills them indirectly by triggering other immune cells to recognize the infected T cell and kill it as part of the immune system's normal function.
As infected T cells die, the immune system generates more to take their place. As new T cells become infected, they are either actively killed or induced to commit suicide. Meanwhile, the HIV virus is not completely hidden from the immune system. As with any infectious agent, HIV presents its proteins to the immune system, which develops antibodies against it. This antibody production, however, is hampered by the fact that HIV mutates rapidly, changing the proteins it displays to the immune system. With each new protein, the immune system must generate new antibodies to fight the infection. Thus, an HIV infection is a dramatic balance between a replicating, ever changing virus and the replenishing stores of T cells that are fighting it. Unfortunately, the immune system, without therapeutic intervention, eventually loses the battle.
Once the CD4 T cells are depleted, the immune system can no longer ward off the daily bombardment of pathogens that all human organisms experience. Common infectious agents thus overwhelm the system, and HIV patients become susceptible to a variety of "opportunistic" diseases that take advantage of the body's reduced ability to fight them off. AIDS doctors report at least twenty-six different opportunistic diseases specific to HIV infection. These include unusual fungal infections such as thrush. The chickenpox virus may come out of dormancy, manifesting itself as the painful disease known as shingles. An obscure form of pneumonia, called pneumocystis pneumonia, is also common in AIDS patients. In addition, patients can acquire cancers such as B-cell lymphoma, which is a cancer of the immune system. Doctors generally consider patients with fewer than 200 CD4 T cells per cubic milliliter of blood as having AIDS. (In contrast, a healthy person counts more than 1,000.)
Anti-Hiv Drug Therapy
Drugs that interfere with viral replication can slow down HIV disease. Early trials relied on the administration of one drug at a time. While patients' health improved and their T cell count rose, in time HIV mutated enough to render the drugs ineffective. Since 1995, however, doctors have found that rotating patients through three different drugs in very high doses significantly improves the health of AIDS patients. Known as "highly active antiretroviral therapy" (HAART), this therapeutic approach also reduces the amount of HIV circulating in the bloodstream to nearly undetectable levels. People infected with HIV who are treated by HAART are now living longer, healthier lives than ever before.
Targeting Life-Cycle Points
Drugs meant to knock out HIV target the activities of two HIV proteins, the reverse transcriptase and the protease. HAART requires drugs of both types. Drugs called protease inhibitors prevent the viral protease from trimming down the large proteins made late during infection. Without those proteins, the viral shell cannot be assembled. In addition, the proteins that reproduce HIV's genetic information, the reverse transcriptase and the integrase, are not functional.
Drugs that inhibit the reverse transcriptase prevent it from copying the RNA into DNA. These drugs work early in the life cycle of HIV. Reverse transcriptase inhibitors include azidothymidine (AZT), whose structure resembles the DNA nucleotide thymine. When reverse transcriptase builds DNA with AZT instead of thymine, the AZT caps the growing DNA molecule and halts DNA production, due to AZT's slight difference in structure from the thymine that DNA production requires.
HIV
Retrovirus associated with AIDS. HIV attacks and gradually destroys the immune system, leaving the host unprotected against infection. It cannot be spread through casual contact but instead is contracted mainly through exposure to blood and blood products (e.g., by sharing hypodermic needles or by accidental needle sticks), semen and female genital secretions, or breast milk. A pregnant woman can pass the virus to her fetus across the placenta. The virus first multiplies in lymph nodes near the site of infection. Once it spreads through the body, usually about 10 years later, symptoms appear, marking the onset of AIDS. Multidrug "cocktails" can delay onset, but missing doses can lead to drug resistance. Like other viruses, HIV needs a host cell to multiply. It attacks helper T cells and can infect other cells. A rapid mutation rate helps it foil both the immune system and treatment attempts. No vaccine or cure exists. Abstinence from sex, use of condoms or other means to prevent sexual transmission of the disease, and avoidance of needle sharing have reduced infection rates in some areas.
HIV (Human Immunodeficiency Virus), either of two closely related retroviruses that invade T-helper lymphocytes and are responsible for AIDS. There are two types of HIV: HIV-1 and HIV-2. HIV-1 is responsible for the vast majority of AIDS in the United States. HIV-2, seen more often in western Africa, has a slower course than HIV-1. There are many strains of both types and the virus mutates rapidly, a trait that has made it especially difficult for researchers to find an effective treatment or vaccine. In many cases, a person's immune system will fight off the invasion of HIV for many years, producing billions of CD4 cells daily, always trying to keep up with the HIV's mutations, before it succumbs and permits the well-known signs of AIDS to develop.
HIV is especially lethal because it attacks the very immune system cells (variously called T4, CD4, or T-helper lymphocytes) that would ordinarily fight off such a viral infection. Receptors on these cells appear to enable the viral RNA to enter the cell. As with all retroviruses, once the RNA is inside the cell, an enzyme called reverse transcriptase allows it to act as the template for its own RNA to DNA transcription. The resultant viral DNA inserts itself into a cell's DNA and is reproduced along with the cell and its daughters.
The exact origin of the virus in humans is unclear. Scientists surmise that it jumped from an animal population, probably African monkeys or chimpanzees, to humans via a bite or meat. The first case documented in humans dates from 1959. The virus was isolated by Luc Montagnier of France's Pasteur Institute in 1983. It went through several name changes before the official name, human immunodeficiency virus, was agreed upon.
Sunday, December 30, 2007
HIV/AIDS
Epidemiology
HIV-1 has spread worldwide, infecting more than 36 million people by 2001. HIV-2, which seems to be less clinically severe and possibly less transmissible from person to person, has mainly been a public health problem for West African nations. Originally epidemic in African and urban settings, HIV and AIDS are now among the most common serious infections globally, including in the Americas and Eurasia and in rural settings. All ages, racial and ethnic groups, and persons of all sexual orientations have been infected.
Virology
HIVs are all members of the family known as retroviruses, so named because of their unique method of reproduction which uses the enzyme (protein catalyst) reverse transcriptase (RT) to incorporate its genetic material (RNA) into the DNA of the infected host's cells. HIV infects specific white blood cells of the host's immune system, known as T-helper lymphocytes (often referred to as CD4+ cells), and destroys them. Even though the immune system produces millions of new CD4+ cells every day, HIV destroys them just as rapidly. The genetic material of HIV has been sequenced, providing a database useful for research on vaccine and antiviral drug development. Many subtypes of HIV-1 have been characterized, but all are transmitted via the same routes and result in the same immunodeficiency.
Symptoms, Diagnosis, and Treatment
Persons initially infected with HIV may develop an "acute retroviral syndrome" characterized by fever, lymph node enlargement, and flu-like symptoms. If symptoms are present, they clear spontaneously, but all infected persons, both with and without symptoms, remain infected and infectious to others indefinitely. The incubation period is highly variable, averaging about a decade, but ranging from a few months or years to possibly longer than two decades. When sufficient damage to the immune system has been sustained, measured either by laboratory cell counts of the Thelper cells or by onset of opportunistic infections, the patient is said to have AIDS. Common manifestations of HIV infection include tiredness, lymph node enlargement, fever, weight loss, and yeast infections of the mouth and vagina.
HIV infection is diagnosed by laboratory detection of evidence of infection, usually identification of HIV-specific antibodies in a blood, oral fluid, or urine specimen. AIDS can be diagnosed in HIV-infected persons in several ways, based on either laboratory evidence of immunodeficiency (lowered levels of CD4+ cells), or clinically by onset of any one or more of a specific list of opportunistic diseases. Opportunistic diseases are those that occur only, or most severely, in patients whose immune systems are impaired. The most common opportunistic diseases in AIDS patients are Pneumocystis carinii pneumonia, Kaposi's sarcoma, toxoplasmosis of the brain, tuberculosis and other mycobacterial infections, and severe herpes, cytomegalo virus, and yeast infections.
As of 2001, all of the more than seventeen antiviral drugs used to treat HIV infection act by interfering with one of the enzymes that HIV needs to complete its life cycle. No treatments result in a cure for HIV infection. The antiviral drugs prevent HIV from growing and further damaging the host's immune system. Thus, the goal of treatment is to preserve the patient's health. Patients must take several antiviral drugs daily. Research on more and better antiviral drugs, and on methods to reconstitute the impaired immune system, is ongoing. A key part of treatment is the prevention of opportunistic infections with specific vaccines and antibiotics.
Prevention
Prevention of HIV infections is deceptively simple: Refrain from having sexual contact and from sharing drug-injecting paraphernalia with anyone who is infected. However, the rapid and continuing global spread of HIV, despite its well-known and severe clinical consequences, points out how difficult it is to change risky sexual and drug-taking behaviors. Many successful educational and social interventions have been demonstrated, but sustaining them in large populations for long periods requires extensive resources and a strong public health commitment. For example, latex condoms effectively prevent sexual transmission of HIV, but making them available and educating infected persons or their sex partners to use them correctly and consistently has been accomplished only with extraordinary efforts in a few nations or settings. Some prevention efforts are considered controversial or are opposed by religious or other groups who interpret prevention efforts to reflect an acceptance of behaviors they do not condone on moral grounds.
The research effort to develop a vaccine to prevent HIV infection has been intense, but the biologic obstacles to success are immense and unprecedented. Because HIV permanently infects cells of the immune system, infection of a single cell results in lifelong infection for the host. Thus, a completely effective vaccine would need to prevent even a single cell from becoming infected. No such vaccine exists for any infection, so HIV will require a new vaccine paradigm. Possible lines of research include stimulating the immune system to detect and eliminate HIV-infected cells, or genetically transforming the HIV in an infected person so as to render it nonvirulent.
Further information on HIV and AIDS is widely available in many user-friendly and scholarly formats. The Internet is a rich source of information, with sites sponsored by public health agencies, such as the Joint United Nations Programme on HIV/AIDS and the Centers for Disease Control and Prevention particularly recommended. Several texts, popular books, and scholarly journals have been devoted exclusively to AIDS public health issues and scientific research. The first of December has been designated World AIDS Day, and many governments, schools, and organizations sponsor community and educational events to coincide with that date each year.
Acquired immune deficiency syndrome or acquired immunodeficiency syndrome (AIDS or Aids) is a collection of symptoms and infections resulting from the specific damage to the immune system caused by the human immunodeficiency virus (HIV) in humans,[1] and similar viruses in other species (SIV, FIV, etc.). The late stage of the condition leaves individuals susceptible to opportunistic infections and tumors. Although treatments for AIDS and HIV exist to decelerate the virus' progression, there is currently no known cure. HIV, et al., are transmitted through direct contact of a mucous membrane or the bloodstream with a bodily fluid containing HIV, such as blood, semen, vaginal fluid, preseminal fluid, and breast milk.[2][3] This transmission can come in the form of anal, vaginal or oral sex, blood transfusion, contaminated hypodermic needles, exchange between mother and baby during pregnancy, childbirth, or breastfeeding, or other exposure to one of the above bodily fluids.
Most researchers believe that HIV originated in sub-Saharan Africa during the twentieth century;[4] it is now a pandemic, with an estimated 33.2 million people now living with the disease worldwide.[5] As of January 2006, the Joint United Nations Programme on HIV/AIDS (UNAIDS) and the World Health Organization (WHO) estimate that AIDS has killed more than 25 million people since it was first recognized on June 5, 1981, making it one of the most destructive epidemics in recorded history. In 2005 alone, AIDS claimed an estimated 2.4–3.3 million lives, of which more than 570,000 were children.[6] A third of these deaths are occurring in sub-Saharan Africa, retarding economic growth and destroying human capital. Antiretroviral treatment reduces both the mortality and the morbidity of HIV infection, but routine access to antiretroviral medication is not available in all countries.[7] HIV/AIDS stigma is more severe than that associated with other life-threatening conditions and extends beyond the disease itself to providers and even volunteers involved with the care of people living with HIV.
AIDS is the most severe acceleration of infection with HIV. HIV is a retrovirus that primarily infects vital organs of the human immune system such as CD4+ T cells (a subset of T cells), macrophages and dendritic cells. It directly and indirectly destroys CD4+ T cells.[8] CD4+ T cells are required for the proper functioning of the immune system. When HIV kills CD4+ T cells so that there are fewer than 200 CD4+ T cells per microliter (µL) of blood, cellular immunity is lost. In some countries, such as the United States, this leads to a diagnosis of AIDS. In other jurisdictions, such as in Canada, AIDS is only diagnosed when a person infected with HIV is diagnosed with one or more of several AIDS-related opportunistic infections or cancers[9][10][11]. Acute HIV infection progresses over time to clinical latent HIV infection and then to early symptomatic HIV infection and later to AIDS, which is identified either on the basis of the amount of CD4+ T cells in the blood, and/or the presence of certain infections, as noted above.
In the absence of antiretroviral therapy, the median time of progression from HIV infection to AIDS is nine to ten years, and the median survival time after developing AIDS is only 9.2 months.[12] However, the rate of clinical disease progression varies widely between individuals, from two weeks up to 20 years. Many factors affect the rate of progression. These include factors that influence the body's ability to defend against HIV such as the infected person's general immune function.[13][14] Older people have weaker immune systems, and therefore have a greater risk of rapid disease progression than younger people. Poor access to health care and the existence of coexisting infections such as tuberculosis also may predispose people to faster disease progression.[12][15][16] The infected person's genetic inheritance plays an important role and some people are resistant to certain strains of HIV. An example of this is people with the CCR5-Δ32 mutation are resistant to infection with certain strains of HIV.[17] HIV is genetically variable and exists as different strains, which cause different rates of clinical disease progression.[18][19][20] The use of highly active antiretroviral therapy prolongs both the median time of progression to AIDS and the median survival time.
The symptoms of AIDS are primarily the result of conditions that do not normally develop in individuals with healthy immune systems. Most of these conditions are infections caused by bacteria, viruses, fungi and parasites that are normally controlled by the elements of the immune system that HIV damages. Opportunistic infections are common in people with AIDS.[30] HIV affects nearly every organ system. People with AIDS also have an increased risk of developing various cancers such as Kaposi's sarcoma, cervical cancer and cancers of the immune system known as lymphomas.
Additionally, people with AIDS often have systemic symptoms of infection like fevers, sweats (particularly at night), swollen glands, chills, weakness, and weight loss.[31][32] After the diagnosis of AIDS is made, the current average survival time with antiretroviral therapy (as of 2005) is estimated to be more than 5 years,[33] but because new treatments continue to be developed and because HIV continues to evolve resistance to treatments, estimates of survival time are likely to continue to change. Without antiretroviral therapy, death normally occurs within a year.[12] Most patients die from opportunistic infections or malignancies associated with the progressive failure of the immune system.[34]
The rate of clinical disease progression varies widely between individuals and has been shown to be affected by many factors such as host susceptibility and immune function[13][14][17] health care and co-infections,[12][34] as well as factors relating to the viral strain.[19][35][36] The specific opportunistic infections that AIDS patients develop depend in part on the prevalence of these infections in the geographic area in which the patient lives.
CO2
Oxygen
In science, oxygen is a colorless, odorless, tasteless, gaseous chemical element with the chemical symbol O and atomic number 8. It is a group 16, nonmetallic, divalent element that is known to form binary compounds (known as oxides) with almost all the other elements. Oxygen has a valence of -2. On Earth it is usually bonded to other elements covalently or ionically. Oxygen is the 3rd most abundant element in the universe by mass after hydrogen and helium, the most abundant element by mass in the Earth's crust, as well as the most abundant element by mass in the human body.[1]
The word oxygen derives from two roots in Greek, οξύς (oxys) (acid, lit. "sharp," from the taste of acids) and -γενής (-genēs) (producer, lit. begetter). It was recognized in 1777 by Antoine Lavoisier, who coined the name oxygen from the Greek roots mentioned above because he erroneously thought that it was a constituent of all acids.[2]
Diatomic oxygen or dioxygen (O2) is one of the two major components of air (20.95%); the other major component is nitrogen. Oxygen is produced from water by plants during photosynthesis, and is necessary for aerobic respiration in animals. Without oxygen, most organisms will die within minutes.[3] It is toxic to obligate anaerobic organisms and was a poisonous waste product for early life on Earth. Triatomic oxygen (ozone, O3) forms through radiation in the upper layers of the atmosphere and acts as a shield against UV radiation.[2]
The most familiar oxygen compound is water. Other well-known examples include silica (found in sand, glass, rock, etc.), and the compounds of carbon and oxygen, such as carbon dioxide (CO2), alcohols (R-OH where "R" is an organic group), carbonyls (R-CO-H or R-CO-R) such as acetone; and carboxylic acids (R-COOH) such as fatty acids. Oxygenated radicals such as perchlorates (ClO4−) and nitrates (NO3−) are strong oxidizing agents in and of themselves. Phosphorus is biologically important in its oxygenated form as the phosphate (PO43−) ion and as the backbone of RNA and DNA. Many metals bond with oxygen atoms, such as iron in iron(III) oxide (Fe2O3), commonly called ru
The common allotrope of elemental oxygen on Earth, O2, is known as dioxygen. Elemental oxygen is most commonly encountered in this form, as about 21% (by volume) of the Earth's atmosphere. O2 has a bond length of 121 pm and a bond energy of 498 kJ/mol.[18]
Ozone (O3), the less common triatomic allotrope of oxygen, is a poisonous gas with a distinct, sharp odor. It was named ozone by Christian Friedrich Schönbein, in 1840, from the Greek word ÖĮώ (ozo) for smell. [2] It is thermodynamically unstable toward the more common dioxygen form. It is formed continuously in the upper atmosphere of the Earth by short-wave ultraviolet (UV) radiation, and also functions as a shield against UV radiation reaching the ground (see ozone layer).[2] Ozone is also formed by electrostatic discharge in the presence of molecular oxygen. The immune system produces ozone as anicrobial (see below). Liquid and solid O3 have a deeper blue color than ordinary oxygen and they are unstable and explosive. Traces of it can be detected as a sharp, chlorine-like smell coming from electric motors, laser printers and photocopiers.
A newly discovered allotrope of oxygen, tetraoxygen (O4), is a deep red solid that is created by pressurizing O2 to the order of 20 GPa. Its properties are being studied for use in rocket fuels and similar applications, as it is a much more powerful oxidizer than either O2 or O3.[19][20] When tetraoxygen is subjected to a pressure of 96 GPa, it becomes metallic, similarly to hydrogen, and becomes more similar to the heavier chalcogens, such as tellurium and polonium, both of which show significant metallic character.
Oxygen has 17 known isotopes with atomic masses ranging from 12.03 u to 28.06 u. Three are stable, 16O, 17O, and 18O, of which 16O is the most abundant (over 99.7%). The radioisotopes all have half-lives of less than three minutes. Nonetheless, 15O was experimentally used in positron emission tomography.
An atomic mass of 16 was assigned to oxygen prior to the definition of the unified atomic mass unit based upon 12C. Since physicists referred to 16O only, while chemists meant the naturally abundant mixture of isotopes, this led to slightly different atomic mass scales.
The isotopic composition of oxygen atoms in the earth's atmosphere is 99.759% 16O, 0.037% 17O and 0.204% 18O.[8] Water on earth is composed of slightly less 18O than air, with seawater containing 0.1995% of this heavier isotope and fresh water containing 0.1981%.[8] Fresh water contains less 18O because water molecules containing the lighter isotopes are slightly more likely to evaporate and fall as precipitation.
Oxygen constitutes 49.2% of the Earth's crust by mass[23] and is the most common component of the world's oceans (88.81% by mass).[8] It is also the second most common component of the Earth's atmosphere, taking up 20.947% of its volume and 23.14% of its mass (some million billion tonnes).[24][8][25] The Earth is unusual in having such a high concentration of free oxygen in its atmosphere. With only 0.15% oxygen by volume, the atmosphere of Mars has the second most abundant concentration by volume of oxygen of any planet in the solar system and Venus comes in third place.[21] However, their oxygen is only produced by ultraviolet radiation impacting oxygen-containing molecules such as carbon dioxide.
Elemental oxygen also occurs in solution in the world's water bodies. At 25°C under 1 atm of air, a litre of water will dissolve about 6.04 cc (8.63 mg, 0.270 mmol) of oxygen, whereas sea water will dissolve about 4.9 cc (7.0 mg, 0.22 mmol). At 0°C the solubilities increase to 10.29 cc (14.7 mg, 0.460 mmol) for water and 8.0 cc (11.4 mg, 0.36 mmol) for sea water. This difference has important implications for ocean life, as polar oceans support a much higher density of life due to their oxygen content.[28] Polluted water often reduces the amount of oxygen in it by killing off oxygen producing plants, bacteria and algae. Scientists assess this aspect of water quality by measuring the water's biochemical oxygen demand (BOD), or the amount of oxygen needed to restore a normal oxygen concentration.[29]
In nature, free oxygen is produced by the light-driven splitting of water during oxygenic photosynthesis in cyanobacteria, green algae and plants.[30] Algae and cyanobacteria in marine environments provide about 70% of the free oxygen produced on earth.[31] The remainder is produced by terrestrial plants, although almost all oxygen produced in tropical forests is consumed by organisms in those forests.[32]
The formula for photosynthesis is:
Two major methods are employed to produce the 100 million tonnes of oxygen extracted from air for industrial uses annually.[10] The most common method is to fractionally distill liquefied air into its various components, with nitrogen distilling as a vapor while oxygen is left as a liquid.[10]
Oxygen can also be produced through electrolysis of water into oxygen and hydrogen. A similar method is the electrocatalytic oxygen evolution from oxides and oxoacids. Chemical catalysts can be used as well, such as in chemical oxygen generators or oxygen candles that are used as part of the life support equipment on submarines, and which are still part of standard equipment on commercial airliners in case of depressurization emergencies.
Another air separation technology involves forcing air to dissolve through ceramic membranes based on zirconium oxide by either high pressure or an electric current, to produce nearly pure oxygen.[29]
In large quantities, the price of liquid oxygen (2001) is approximately $0.21/kg. [34] Since the primary cost of production is the energy cost of liquefying the air, the production cost will change as energy cost varies.
Oxygen is often transported in bulk as a liquid in specially insulated tankers because one liter of liquefied oxygen is equivalent to 840 liters of gaseous oxygen, at atmospheric pressure and 20 °C.[10] Such tankers are used to refill bulk liquid oxygen storage containers, which stand outside hospitals and other institutions with a need for large volumes of pure oxygen. Liquid oxygen is passed through heat-exchangers, which convert the cryogenic liquid into gas before it enters the building. Oxygen is also stored and shipped in smaller pressure cylinders containing the compressed gas; a form that is useful in certain portable medical applications and Oxy-fuel welding and cutting.[10]
Uptake of oxygen from the air is the essential purpose of respiration, so oxygen supplementation is used in medicine. Oxygen therapy is used to treat emphysema, pneumonia, some heart disorders and any disease that impairs the body's ability to take up and use oxygen.[35] Treatments are flexible enough to be used in hospitals, the patient's home, or increasingly by portable devices. Oxygen tents were once commonly used in oxygen supplementation, but have since been mostly replaced by the use of oxygen masks or nasal cannulas. Hyperbaric medicine uses hyperbaric oxygen chambers to increase the partial pressure of oxygen around the patient and, when needed, the medical staff. Carbon monoxide poisoning, gas gangrene and decompression sickness (the "bends") are sometimes treated using these devices.[35][36]
People who climb mountains or fly in non-pressurized fixed-wing aircraft sometimes have supplemental oxygen supplies.[37] Passengers traveling in commercial airplanes have an emergency supply of oxygen automatically supplied to them in case of cabin depressurization. Sudden cabin pressure loss activates chemical oxygen generators above each seat, causing oxygen masks to drop and forcing iron fillings into the sodium chlorate inside the canister.[29] A steady stream of oxygen gas is produced by the exothermic reaction. A ValuJet airplane crashed after life-expired oxygen canisters, which were being shipped in the cargo hold, activated and burned a hole in the airplane. They were miss-labelled as empty; and were being carried in the hold in contravention of the Dangerous Goods regulations.[38]
A notable application of oxygen as a low-pressure breathing gas is in modern spacesuits, which surround their occupant's body with pressurized air. These devices use nearly pure oxygen at about one third normal pressure, resulting in a normal blood partial pressures of oxygen. This trade-off of higher oxygen concentration for lower pressure is needed to maintain flexible spacesuits.
Oxygen, as a supposed mild euphoric, has a history of recreational use (see oxygen bar). However, the reality of a pharmacological effect is doubtful, a placebo or psychological boost being the most plausible explanation.
In the 19th century, oxygen was often mixed with nitrous oxide to temper its analgesic effect. A stable 50% gaseous mixture (Entonox) is commonly used in medicine today as an analgesic. However, the common basic anesthetic mixture is 30% oxygen with 70% nitrous oxide; the pain-suppressing effects, obviously, are due to the nitrous oxide and not to oxygen.
Smelting of iron ore into steel consumes 55% of commercially produced oxygen.[29] In this process, oxygen is injected through a high-pressure lance into molten iron, which removes sulfur and carbon impurities. The reaction is exothermic, so the temperature increases to 1700 ° C.[29]
Another 25% of commercially produced oxygen is used by the chemical industry.[29] Ethylene is reacted with oxygen to create ethylene oxide, which in turn is converted into ethylene glycol; the primary feeder material used to manufacture a host of products, including antifreeze and polyester polymers (the precursors of many plastics and fabrics).[29]
Most of the remaining 20% of commercially produced oxygen is used in medical applications, metal cutting and welding, as an oxidizer in rocket fuel, and in water treatment.[29] Oxygen is used in oxyacetylene welding burning acetylene with oxygen to produce a very hot flame. In this process, metal up to 60 cm thick is first heated with a small oxy-acetylene flame and then quickly cut by a large stream of oxygen.[39][40] Rocket propulsion requires a fuel and an oxidizer. Larger rockets use liquid oxygen as their oxidizer, which is mixed and ignited with the fuel for propulsion.
Paleoclimatologists measure the ratio of oxygen-18 and oxygen-16 in the shells and skeletons of marine organisms to determine what the climate was like millions of years ago. During periods of lower global temperatures, sea water molecules that contain the lighter isotope, oxygen-16, evaporate at a slightly faster rate than water molecules containing the 12% heavier oxygen-18.[41] Snow and rain from that evaporated water tends to be enriched in oxygen-16 and the seawater left behind tends to be enriched in oxygen-18. Marine organisms then incorporate more oxygen-18 into their skeletons and shells than they would in a warmer climate.[41] Paleoclimatologists also directly measure this ratio in air trapped in ice core samples that are up to several hundreds of thousand years old.
Oxygen presents two spectrophotometric absorption bands peaking at the wavelengths 687 and 760 nanometers. Some scientists have proposed to use the measurement of the radiance coming from vegetation canopies in those oxygen bands to characterize plant health status from a satellite platform.[42] This is because in those bands, it is possible to discriminate the vegetation's reflectance from the vegetation's fluorescence, which is much weaker. The measurement presents several technical difficulties due to the low signal to noise ratio and due to the vegetation's architecture, but it has been proposed as a possibility to monitor the carbon cycle from satellites on a global scale.
Since there are no known ways but the presence of life for planetary atmospheres to maintain high concentrations of oxygen, these same absorption bands have been proposed as a way (when telescopes have improved significantly) to search planets of nearby stars spectrophotometrically for signs of life-as-we-know-it.
In almost all known compounds of oxygen, the oxidation state of oxygen is -2. In a few compounds such as peroxides, the oxidation state is -1. Other oxidation states are quite rare such as:-1/3 (ozonides), +1 (oxygen(I) fluoride) and +2 (oxygen fluoride). The most familiar oxygen-containing compound is H2O. Other well-known examples include silica (found in sand, glass, rock, etc.), and the compounds of carbon and oxygen, such as carbon dioxide (CO2), alcohols (R-OH), carbonyls, (R-CO-H or R-CO-R), and carboxylic acids (R-COOH). Oxygenated radicals such as chlorates (ClO3−), perchlorates (ClO4−), chromates (CrO42−), dichromates (Cr2O72−), permanganates (MnO4−), and nitrates (NO3−) are strong oxidizing agents in and of themselves. Phosphorus is biologically important in its oxygenated form as the phosphate (PO43−) ion. Many metals bond with oxygen atoms, such as iron in iron(III) oxide (Fe2O3), commonly called rust.
One unexpected oxygen compound is dioxygen hexafluoroplatinate O2+PtF6−. It was discovered when Neil Bartlett was studying the properties of platinum hexafluoride (PtF6).[43] He noticed a change in color when this compound was exposed to atmospheric air. Bartlett reasoned that xenon should be oxidized by PtF6. This led him to the discovery of xenon hexafluoroplatinate Xe+PtF6−.Epoxides are ethers in which the oxygen atom is part of a ring of three atoms. O22+ is another cation as in O2F2, it is only formed in the presence of stronger oxidants than oxygen, which limits this cation to oxygen fluorines, e.g. oxygen fluoride.[44]
When dissolved in water, many metallic oxides form alkaline solutions while many oxides of nonmetals form acidic solutions. For example, sodium oxide in solution forms the strong base sodium hydroxide while phosphorus pentoxide in solution forms phosphoric acid.[45]
Although oxygen molecules are not generally reactive at room temperature they do react with certain strong inorganic reducing substances, such as ferrous sulfate in aqueous solution.[45] Oxygen also reacts spontaneously with many organic compounds at or below room temperature in a process called autoxidation.[45] Other substances need to be heated before they will react with oxygen in bulk but some, such as iron, readily forms iron oxide, or rust.
Due to its electronegativity, oxygen forms chemical bonds with almost all other free elements at elevated temperatures to give corresponding oxides. The only elements known to escape the possibility of combination with oxygen are a few of the noble gases and fluorine. So-called noble metals (common examples: gold, platinum) resist direct chemical combination with oxygen, and substances like gold(III) oxide must be formed by an indirect route.
Peroxides retain some of oxygen's original molecular structure. White or light yellow sodium peroxide (Na2O2) is formed when metallic sodium (Na) is burned in oxygen. Each oxygen atom in it's peroxide ion may have a full octet of 4 pairs of electrons.[46] Superoxides are a class of compounds that are very similar to peroxides, but with just one unpaired electron for each pair of oxygen atoms.[46]. These compounds form from oxidation of alkali metals with larger ionic radii (K, Rb, Cs). For example, Potassium superoxide ( KO2) is an orange-yellow solid formed when potassium (K) reacts with oxygen.
Hydrogen peroxide (H2O2) can be produced by passing a volume of 96 to 98% hydrogen and 2 to 4% oxygen through an electric discharge.[45] A more commercially viable method is allow autoxidation of an organic intermediate; 2-ethylanthrahydroquinone dissolved in an organic solvent is oxidized to H2O2 and 2-ethylanthraquinone.[45] The 2-ethylanthraquinone is then reduced and recycled back into the process.
Most chemically combined oxygen is locked in a class of minerals called silicates (which in turn are the major component of rocks and clays). The basic structure of silicates consists of two parts; units of silicon surrounded by four oxygen anions in a tetrahedral arrangement and units of metal-oxygen polyhedra that contain metal cations (examples: aluminium, calcium, iron and sodium).[46] Both units are linked together by sharing oxygen anions, forming complex polymers in the process.
Water- soluble silicates in the form of Na4SiO4, Na2SiO3, and Na2Si2O5 are used as detergents and adhesives.[46] NaxSixOx with a higher ratio of SiO2 to Na2O has a greater molecular weight and a lower solubility. Silica is a crystalline polymer with the chemical formula (SiO2)n. Quartz is the mineral form of silica in nature and the most common deposits of quartz are in sand.
Most of the thousands of organic compounds that contain oxygen are not made by direct action of oxygen. Many of the compounds that are directly created by a reaction with oxygen are commercially important. Examples and the reactions that form them include:[47]
Acetone ((CH3)2CO) and phenol (C6H5OH) are used as feeder materials in the synthesis of many different substances. The cumene (C6H5-CH(CH3)2) in the below reaction is commonly derived from petroleum.
C6H5-CH(CH3)2 + O2 -> C6H5-COOH(CH3)2 -> (CH3)2CO + C6H5OH
Acetylene (C2H2) along with a mix of carbon monoxide, hydrogen and water are formed directly by the oxidation of natural gas in the below simplified equation.[48]
CH4 + C2H6 + O2 -> C2H2 + CO + 3H2 + H2O
Ethylene oxide (C2H4O) is used to make the antifreeze ethylene glycol.
C2H4 + 1/2 O2 -catalyst-> C2H4O
Peracetic acid (CH3(COOH)O) is the feeder material used to make various epoxy compounds.
CH3CHO + O2 -catalyst-> CH3(COOH)O
from the lungs of most animals
Parts of DNA are made of oxygen and the element is found in almost all molecules that are important to life. Molecular oxygen, O2, is essential for cellular respiration in all aerobic organisms. Almost all animals use hemoglobin in their blood to transport oxygen from their lungs to their tissues, but some, such as spiders and lobsters, use hemerythrin.[24] A liter of blood can dissolve 200 cc of oxygen gas, which is much more than water can dissolve.[24] The below description of oxygen uptake and use is typical for vertebrates.
Oxygen diffuses through membranes and into red blood cells after inhalation into the lungs. The Heme group of hemoglobin by now already has carbon dioxide in its active site, but releases it for exhalation when oxygen is present. After being carried in blood to a body tissue in need of oxygen, it is handed-off from the Heme group to monooxygenase, an enzyme that also has an active site with an atom of iron.[24] Monooxygenase uses oxygen to catalyze many oxidation reactions in the body. Oxygen is also used as an electron acceptor in mitochondria to generate chemical energy in the form of adenosine triphosphate (ATP) during oxidative phosphorylation. Carbon dioxide, one of the waste products produced, is released from the cell and into the blood, where it combines with empty Heme groups. Blood circulates back to the lungs and the process repeats.[49] On average, a oxygen atom is used in respiration once every 3,000 years.[12]
Reactive oxygen species are dangerous by-products that sometimes result from the use of oxygen in organisms. Important examples include; oxygen free radicals such as the highly dangerous superoxide O2-, and the less harmful hydrogen peroxide ( H2O2).[24] The body uses superoxide dismutase to reduce superoxide radicals to hydrogen peroxide. Glutathione peroxidase and similar enzymes, then convent the H2O2 to water and dioxygen.[24]
Parts of the immune system of higher organisms, however, create peroxide, superoxide and singlet oxygen to destroy invading microbes. Recently, singlet oxygen has been found to be a source of biologically-produced ozone: this reaction proceeds through an unusual compound dihydrogen trioxide, also known as trioxidane, (HOOOH) which is an antibody-catalyzed product of singlet oxygen and water. This compound in turn disproportionates to ozone and peroxide, providing two powerful antibacterials. The body's range of defense against all of these active oxidizing agents is hardly surprising, then, given their "deliberate" employment as antimicrobial agents in the immune response.[50]
Oxygen was almost nonexistent in earth's atmosphere before the evolution of water oxidation in photosynthetic bacteria. Free oxygen first appeared in significant quantities during the Paleoproterozoic era (between 2.5 billion years ago and 1.6 billion years ago) as a product of the metabolic action of early anaerobes (archaea and bacteria). These organisms developed the mechanism of oxygen evolution between 3.5 and 2.7 billion years ago. At first, the produced oxygen dissolved in the oceans and reacted with iron, creating banded iron formations. It started to gas out of the oxygen-saturated waters about 2.7 billion years ago as evident in the rusting of iron-rich terrestrial rocks starting around that time. The amount of oxygen in the atmosphere increased gradually at first and shot up rapidly around 2.2 to 1.7 billion years ago to about 10% of its present level.[51]
The development of an oxygen-rich atmosphere was one of the most important events in the history of life on earth. The presence of large amounts of dissolved and free oxygen in the oceans and atmosphere may have driven most of the anaerobic organisms then living to extinction during the oxygen catastrophe about 2.4 billion years ago. However, the high electronegativity of O2 creates a large potential energy drop for cellular respiration, thus enabling organisms using aerobic respiration to produce much more ATP than anaerobic organisms. This makes them so efficient that they have come to dominate earth's biosphere.[52] Photosynthesis and cellular respiration of oxygen allowed for the evolution of eukaryotic cells and ultimately complex multicellular organisms such as plants and animals.
The atmospheric abundance of free oxygen in later geological epochs and its gradual increase up to the present has been largely due to synthesis by photosynthetic organisms. Over the past 500 million years, oxygen levels fluctuated between 15 and 35% per volume. Towards the end of the Carboniferous era (coal age) about 300 million years ago, atmospheric oxygen levels reached a maximum of 35% by volume, allowing insects and amphibians with limiting respiratory systems to grow much larger than today's species. Today, oxygen is the second most common component of the earth's atmosphere (about 21% by volume) after nitrogen. Human activities, including the burning of 7 billion tonnes of fossil fuels each year have had very little effect on the amount of free oxygen in the atmosphere.[12]
Oxygen is the most common of all chemical elements on earth, being found in water, air, and most mineral and organic substances, including most compounds in the human body. It combines with almost all other elements, and is so reactive that it was given the Greek name ‘oxygen’, meaning acid-forming. However, most of the compounds it forms are not acids. Its chemical reactions usually form heat (as in the animal body) and sometimes light (as in candles).
It has always been known that animals cannot live without air, but in 1674 Mayow showed that only one part of the air, about one-fifth, is essential for life, and named it ‘vital air’. A hundred years later Priestley isolated this part, oxygen; Lavoisier purified oxygen and its properties began to be studied.
Atmospheric air contains 21% oxygen, at a pressure of about 150 mm Hg varying with barometric pressure and to a small extent with humidity. It enters the lungs during breathing and is absorbed into the blood passively by diffusion, combining with haemoglobin and being carried in the bloodstream to all parts of the body. There it is used to metabolize or ‘burn’ foodstuffs in the cells, especially fats and carbohydrates, providing heat and creating new chemical compounds, water, and the waste product carbon dioxide. Tissues and organs vary in the length of time they can survive without oxygen, according to their provision for anaerobic metabolism. The brain cannot survive without oxygen; the cessation of breathing will cause unconsciousness in a few minutes, and death soon afterwards. Other tissues such as skeletal muscle can continue to work for a limited time, when glycogen stores are broken down without oxygen to provide energy; lactic acid is a by-product that leaks into the blood and makes it more acid, but can be recycled into carbohydrate stores in the liver.
In quiet breathing at rest we absorb about 0.2-0.3 litres/min of oxygen (depending on body size), but in vigorous exercise this can go up to over 2 litres/min. This increase is accomplished by increased breathing (which supplies oxygen to the lungs at a greater rate), increased cardiac output and flow of blood to the muscles, and greater extraction of oxygen from the blood by the muscles. If the oxygen supply to the muscles is inadequate then the anaerobic threshold is passed and anaerobic metabolism takes place, with production of lactic acid. After the exercise additional oxygen is needed to convert the lactic acid back to glycogen, and breathing remains enhanced while the oxygen debt is repaid.
The supply of oxygen to the body depends not on the percentage in the air breathed but on its tension or pressure. At high altitude, say 5000 metres above sea level, the percentage of oxygen is still 21%, but because atmospheric pressure is halved, the oxygen pressure is half that at sea level — 75 mm Hg rather than 150 mm Hg. A person may as a result suffer from hypoxia — a lack of oxygen.
High oxygen pressures can be harmful and cause oxygen poisoning, including lung damage and brain dysfunction. In nature high oxygen pressures only exist in deep water diving, and mankind has not had to evolve ways of combating them. Once scientists had purified oxygen it became possible to administer it to patients; this has life-saving possibilities, but care has to be taken not to exceed the toxic level.
Some compounds rich in oxygen, such as the pollutant ozone (itself a molecular form of oxygen), and hydrogen peroxide, can react with cells to produce strongly reactive forms of oxygen. Superoxide anions and unstable oxygen free radicals (such as hydroxyl and hydroperoxy radicals) can be toxic to cells, by way of excess lipid peroxidation. These are implicated, for example, in damage following the restoration of blood flow (reperfusion) after the blockage which causes heart attacks or strokes, and in a variety of other disease processes. However the body does have inherent enzymatic defences against free radical accumulation, and there are antioxidants, such as uric acid, ascorbate, and glutathione, which can inactivate them. Free radicals are likely to contribute also to the ageing process: the very substance by which we live may itself limit our lifespan. Thus oxygen, like most good things, can be dangerous in excess.
Mankind evolved to live close to sea level. Climbing mountains (causing hypoxia) and deep-sea diving (causing nitrogen narcosis or oxygen poisoning) can both be dangerous, in the absence of the right precautions.
Oxygen is one of the basic chemical elements. In its most common form, oxygen is a colorless gas found in air. It is one of the life-sustaining elements on Earth and is needed by all animals. Oxygen is also used in many industrial, commercial, medical, and scientific applications. It is used in blast furnaces to make steel, and is an important component in the production of many synthetic chemicals, including ammonia, alcohols, and various plastics. Oxygen and acetylene are combusted together to provide the very high temperatures needed for welding and metal cutting. When oxygen is cooled below -297° F (-183° C), it becomes a pale blue liquid that is used as a rocket fuel.
Oxygen is one of the most abundant chemical elements on Earth. About one-half of the earth's crust is made up of chemical compounds containing oxygen, and a fifth of our atmosphere is oxygen gas. The human body is about two-thirds oxygen. Although oxygen has been present since the beginning of scientific investigation, it wasn't discovered and recognized as a separate element until 1774 when Joseph Priestley of England isolated it by heating mercuric oxide in an inverted test tube with the focused rays of the sun. Priestley described his discovery to the French scientist Antoine Lavoisier, who experimented further and determined that it was one of the two main components of air. Lavoisier named the new gas oxygen using the Greek words oxys, meaning sour or acid, and genes, meaning producing or forming, because he believed it was an essential part of all acids.
In 1895, Karl Paul Gottfried von Linde of Germany and William Hampson of England independently developed a process for lowering the temperature of air until it liquefied. By carefully distillation of the liquid air, the various component gases could be boiled off one at a time and captured. This process quickly became the principal source of high quality oxygen, nitrogen, and argon.
In 1901, compressed oxygen gas was burned with acetylene gas in the first demonstration of oxy-acetylene welding. This technique became a common industrial method of welding and cutting metals.
The first use of liquid rocket propellants came in 1923 when Robert Goddard of the United States developed a rocket engine using gasoline as the fuel and liquid oxygen as the oxidizer. In 1926, he successfully flew a small liquid-fueled rocket a distance of 184 ft (56 m) at a speed of about 60 mph (97 kph).
After World War II, new technologies brought significant improvements to the air separation process used to produce oxygen. Production volumes and purity levels increased while costs decreased. In 1991, over 470 billion cubic feet (13.4 billion cubic meters) of oxygen were produced in the United States, making it the second-largest-volume industrial gas in use.
Worldwide the five largest oxygen-producing areas are Western Europe, Russia (formerly the USSR), the United States, Eastern Europe, and Japan.
Raw Materials
Oxygen can be produced from a number of materials, using several different methods. The most common natural method is photo-synthesis, in which plants use sunlight convert carbon dioxide in the air into oxygen. This offsets the respiration process, in which animals convert oxygen in the air back into carbon dioxide.
The most common commercial method for producing oxygen is the separation of air using either a cryogenic distillation process or a vacuum swing adsorption process. Nitrogen and argon are also produced by separating them from air.
Oxygen can also be produced as the result of a chemical reaction in which oxygen is freed from a chemical compound and becomes a gas. This method is used to generate limited quantities of oxygen for life support on submarines, aircraft, and spacecraft.
Hydrogen and oxygen can be generated by passing an electric current through water and collecting the two gases as they bubble off. Hydrogen forms at the negative terminal and oxygen at the positive terminal. This method is called electrolysis and produces very pure hydrogen and oxygen. It uses a large amount of electrical energy, however, and is not economical for large-volume production.
The Manufacturing
Process
Most commercial oxygen is produced using a variation of the cryogenic distillation process originally developed in 1895. This process produces oxygen that is 99+% pure. More recently, the more energy-efficient vacuum swing adsorption process has been used for a limited number of applications that do not require oxygen with more than 90-93% purity.
Here are the steps used to produce commercial-grade oxygen from air using the cryogenic distillation process.
Pretreating
Because this process utilizes an extremely cold cryogenic section to separate the air, all impurities that might solidify—such as water vapor, carbon dioxide, and certain heavy hydrocarbons—must first be removed to prevent them from freezing and plugging the cryogenic piping.
* The air is compressed to about 94 psi (650 kPa or 6.5 atm) in a multi-stage compressor. It then passes through a water-cooled aftercooler to condense any water vapor, and the condensed water is removed in a water separator.
* The air passes through a molecular sieve adsorber. The adsorber contains zeolite and silica gel-type adsorbents, which trap the carbon dioxide, heavier hydrocarbons, and any remaining traces of water vapor. Periodically the adsorber is flushed clean to remove the trapped impurities. This usually requires two adsorbers operating in parallel, so that one can continue to process the air-flow while the other one is flushed.
Separating
Air is separated into its major components—nitrogen, oxygen, and argon—through a distillation process known as fractional distillation. Sometimes this name is shortened to fractionation, and the vertical structures used to perform this separation are called fractionating columns. In the fractional distillation process, the components are gradually separated in several stages. At each stage the level of concentration, or fraction, of each component is increased until the separation is complete.
Because all distillation processes work on the principle of boiling a liquid to separate one or more of the components, a cryogenic section is required to provide the very low temperatures needed to liquefy the gas components.
* The pretreated air stream is split. A small portion of the air is diverted through a compressor, where its pressure is boosted. It is then cooled and allowed to expand to nearly atmospheric pressure. This expansion rapidly cools the air, which is injected into the cryogenic section to provide the required cold temperatures for operation.
* The main stream of air passes through one side of a pair of plate fin heat exchangers operating in series, while very cold oxygen and nitrogen from the cryogenic section pass through the other side. The incoming air stream is cooled, while the oxygen and nitrogen are warmed. In some operations, the air may be cooled by passing it through an expansion valve instead of the second heat exchanger. In either case, the temperature of the air is lowered to the point where the oxygen, which has the highest boiling point, starts to liquefy.
* The air stream—now part liquid and part gas—enters the base of the high-pressure fractionating column. As the air works its way up the column, it loses additional heat. The oxygen continues to liquefy, forming an oxygen-rich mixture in the bottom of the column, while most of the nitrogen and argon flow to the top as a vapor.
* The liquid oxygen mixture, called crude liquid oxygen, is drawn out of the bottom of the lower fractionating column and is cooled further in the subcooler. Part of this stream is allowed to expand to nearly atmospheric pressure and is fed into the low-pressure fractionating column. As the crude liquid oxygen works its way down the column, most of the remaining nitrogen and argon separate, leaving 99.5% pure oxygen at the bottom of the column.
* Meanwhile, the nitrogen/argon vapor from the top of the high-pressure column is cooled further in the subcooler. The mixed vapor is allowed to expand to nearly atmospheric pressure and is fed into the top of the low-pressure fractionating column. The nitrogen, which has the lowest boiling point, turns to gas first and flows out the top of the column as 99.995% pure nitrogen.
* The argon, which has a boiling point between the oxygen and the nitrogen, remains a vapor and begins to sink as the nitrogen boils off. As the argon vapor reaches a point about two-thirds the way down the column, the argon concentration reaches its maximum of about 7-12% and is drawn off into a third fractionating column, where it is further recirculated and refined. The final product is a stream of crude argon containing 93-96% argon, 2-5% oxygen, and the balance nitrogen with traces of other gases.
Purifying
The oxygen at the bottom of the low-pressure column is about 99.5% pure. Newer cryogenic distillation units are designed to recover more of the argon from the low-pressure column, and this improves the oxygen purity to about 99.8%.
* If higher purity is needed, one or more additional fractionating columns may be added in conjunction with the low-pressure column to further refine the oxygen product. In some cases, the oxygen may also be passed over a catalyst to oxidize any hydrocarbons. This process produces carbon dioxide and water vapor, which are then captured and removed.
Distributing
About 80-90% of the oxygen produced in the United States is distributed to the end users in gas pipelines from nearby air separation plants. In some parts of the country, an extensive network of pipelines serves many end users over an area of hundred of miles (kilometers). The gas is compressed to about 500 psi (3.4 MPa or 34 atm) and flows through pipes that are 4-12 in (10-30 cm) in diameter. Most of the remaining oxygen is distributed in insulated tank trailers or railroad tank cars as liquid oxygen.
* If the oxygen is to be liquefied, this process is usually done within the low-pressure fractionating column of the air separation plant. Nitrogen from the top of the low-pressure column is compressed, cooled, and expanded to liquefy the nitrogen. This liquid nitrogen stream is then fed back into the low-pressure column to provide the additional cooling required to liquefy the oxygen as it sinks to the bottom of the column.
* Because liquid oxygen has a high boiling point, it boils off rapidly and is rarely shipped farther than 500 mi (800 km). It is transported in large, insulated tanks. The tank body is constructed of two shells and the air is evacuated between the inner and outer shell to retard heat loss. The vacuum space is filled with a semisolid insulating material to further halt heat flow from the outside.
Quality Control
The Compressed Gas Association establishes grading standards for both gaseous oxygen and liquid oxygen based on the amount and type of impurities present. Gas grades are called Type I and range from A, which is 99.0% pure, to F, which is 99.995% pure. Liquid grades are called Type II and also range from A to F, although the types and amounts of allowable impurities in liquid grades are different than in gas grades. Type I Grade B and Grade C and Type II Grade C are 99.5% pure and are the most commonly produced grades of oxygen. They are used in steel making and in the manufacture of synthetic chemicals.
The operation of cryogenic distillation airseparation units is monitored by automatic instruments and often uses computer controls. As a result, their output is consistent in quality. Periodic sampling and analysis of the final product ensures that the standards of purity are being met.
The Future
In January 1998, the United States launched the Lunar Prospector satellite into orbit around the moon. Among its many tasks, this satellite will be scanning the surface of the moon for indications of water. Scientists hope that if sufficient quantities of water are found, it could be used to produce hydrogen and oxygen gases through electrolysis, using solar power to generate the electricity. The hydrogen could be used as a fuel, and the oxygen could be used to provide life support for lunar colonies. Another plan involves extracting oxygen from chemical compounds in the lunar soil using a solar-powered furnace for heat.
In science, oxygen is a colorless, odorless, tasteless, gaseous chemical element with the chemical symbol O and atomic number 8. It is a group 16, nonmetallic, divalent element that is known to form binary compounds (known as oxides) with almost all the other elements. Oxygen has a valence of -2. On Earth it is usually bonded to other elements covalently or ionically. Oxygen is the 3rd most abundant element in the universe by mass after hydrogen and helium, the most abundant element by mass in the Earth's crust, as well as the most abundant element by mass in the human body.[1]
The word oxygen derives from two roots in Greek, οξύς (oxys) (acid, lit. "sharp," from the taste of acids) and -γενής (-genēs) (producer, lit. begetter). It was recognized in 1777 by Antoine Lavoisier, who coined the name oxygen from the Greek roots mentioned above because he erroneously thought that it was a constituent of all acids.[2]
Diatomic oxygen or dioxygen (O2) is one of the two major components of air (20.95%); the other major component is nitrogen. Oxygen is produced from water by plants during photosynthesis, and is necessary for aerobic respiration in animals. Without oxygen, most organisms will die within minutes.[3] It is toxic to obligate anaerobic organisms and was a poisonous waste product for early life on Earth. Triatomic oxygen (ozone, O3) forms through radiation in the upper layers of the atmosphere and acts as a shield against UV radiation.[2]
The most familiar oxygen compound is water. Other well-known examples include silica (found in sand, glass, rock, etc.), and the compounds of carbon and oxygen, such as carbon dioxide (CO2), alcohols (R-OH where "R" is an organic group), carbonyls (R-CO-H or R-CO-R) such as acetone; and carboxylic acids (R-COOH) such as fatty acids. Oxygenated radicals such as perchlorates (ClO4−) and nitrates (NO3−) are strong oxidizing agents in and of themselves. Phosphorus is biologically important in its oxygenated form as the phosphate (PO43−) ion and as the backbone of RNA and DNA. Many metals bond with oxygen atoms, such as iron in iron(III) oxide (Fe2O3), commonly called ru
The common allotrope of elemental oxygen on Earth, O2, is known as dioxygen. Elemental oxygen is most commonly encountered in this form, as about 21% (by volume) of the Earth's atmosphere. O2 has a bond length of 121 pm and a bond energy of 498 kJ/mol.[18]
Ozone (O3), the less common triatomic allotrope of oxygen, is a poisonous gas with a distinct, sharp odor. It was named ozone by Christian Friedrich Schönbein, in 1840, from the Greek word ÖĮώ (ozo) for smell. [2] It is thermodynamically unstable toward the more common dioxygen form. It is formed continuously in the upper atmosphere of the Earth by short-wave ultraviolet (UV) radiation, and also functions as a shield against UV radiation reaching the ground (see ozone layer).[2] Ozone is also formed by electrostatic discharge in the presence of molecular oxygen. The immune system produces ozone as anicrobial (see below). Liquid and solid O3 have a deeper blue color than ordinary oxygen and they are unstable and explosive. Traces of it can be detected as a sharp, chlorine-like smell coming from electric motors, laser printers and photocopiers.
A newly discovered allotrope of oxygen, tetraoxygen (O4), is a deep red solid that is created by pressurizing O2 to the order of 20 GPa. Its properties are being studied for use in rocket fuels and similar applications, as it is a much more powerful oxidizer than either O2 or O3.[19][20] When tetraoxygen is subjected to a pressure of 96 GPa, it becomes metallic, similarly to hydrogen, and becomes more similar to the heavier chalcogens, such as tellurium and polonium, both of which show significant metallic character.
Oxygen has 17 known isotopes with atomic masses ranging from 12.03 u to 28.06 u. Three are stable, 16O, 17O, and 18O, of which 16O is the most abundant (over 99.7%). The radioisotopes all have half-lives of less than three minutes. Nonetheless, 15O was experimentally used in positron emission tomography.
An atomic mass of 16 was assigned to oxygen prior to the definition of the unified atomic mass unit based upon 12C. Since physicists referred to 16O only, while chemists meant the naturally abundant mixture of isotopes, this led to slightly different atomic mass scales.
The isotopic composition of oxygen atoms in the earth's atmosphere is 99.759% 16O, 0.037% 17O and 0.204% 18O.[8] Water on earth is composed of slightly less 18O than air, with seawater containing 0.1995% of this heavier isotope and fresh water containing 0.1981%.[8] Fresh water contains less 18O because water molecules containing the lighter isotopes are slightly more likely to evaporate and fall as precipitation.
Oxygen constitutes 49.2% of the Earth's crust by mass[23] and is the most common component of the world's oceans (88.81% by mass).[8] It is also the second most common component of the Earth's atmosphere, taking up 20.947% of its volume and 23.14% of its mass (some million billion tonnes).[24][8][25] The Earth is unusual in having such a high concentration of free oxygen in its atmosphere. With only 0.15% oxygen by volume, the atmosphere of Mars has the second most abundant concentration by volume of oxygen of any planet in the solar system and Venus comes in third place.[21] However, their oxygen is only produced by ultraviolet radiation impacting oxygen-containing molecules such as carbon dioxide.
Elemental oxygen also occurs in solution in the world's water bodies. At 25°C under 1 atm of air, a litre of water will dissolve about 6.04 cc (8.63 mg, 0.270 mmol) of oxygen, whereas sea water will dissolve about 4.9 cc (7.0 mg, 0.22 mmol). At 0°C the solubilities increase to 10.29 cc (14.7 mg, 0.460 mmol) for water and 8.0 cc (11.4 mg, 0.36 mmol) for sea water. This difference has important implications for ocean life, as polar oceans support a much higher density of life due to their oxygen content.[28] Polluted water often reduces the amount of oxygen in it by killing off oxygen producing plants, bacteria and algae. Scientists assess this aspect of water quality by measuring the water's biochemical oxygen demand (BOD), or the amount of oxygen needed to restore a normal oxygen concentration.[29]
In nature, free oxygen is produced by the light-driven splitting of water during oxygenic photosynthesis in cyanobacteria, green algae and plants.[30] Algae and cyanobacteria in marine environments provide about 70% of the free oxygen produced on earth.[31] The remainder is produced by terrestrial plants, although almost all oxygen produced in tropical forests is consumed by organisms in those forests.[32]
The formula for photosynthesis is:
Two major methods are employed to produce the 100 million tonnes of oxygen extracted from air for industrial uses annually.[10] The most common method is to fractionally distill liquefied air into its various components, with nitrogen distilling as a vapor while oxygen is left as a liquid.[10]
Oxygen can also be produced through electrolysis of water into oxygen and hydrogen. A similar method is the electrocatalytic oxygen evolution from oxides and oxoacids. Chemical catalysts can be used as well, such as in chemical oxygen generators or oxygen candles that are used as part of the life support equipment on submarines, and which are still part of standard equipment on commercial airliners in case of depressurization emergencies.
Another air separation technology involves forcing air to dissolve through ceramic membranes based on zirconium oxide by either high pressure or an electric current, to produce nearly pure oxygen.[29]
In large quantities, the price of liquid oxygen (2001) is approximately $0.21/kg. [34] Since the primary cost of production is the energy cost of liquefying the air, the production cost will change as energy cost varies.
Oxygen is often transported in bulk as a liquid in specially insulated tankers because one liter of liquefied oxygen is equivalent to 840 liters of gaseous oxygen, at atmospheric pressure and 20 °C.[10] Such tankers are used to refill bulk liquid oxygen storage containers, which stand outside hospitals and other institutions with a need for large volumes of pure oxygen. Liquid oxygen is passed through heat-exchangers, which convert the cryogenic liquid into gas before it enters the building. Oxygen is also stored and shipped in smaller pressure cylinders containing the compressed gas; a form that is useful in certain portable medical applications and Oxy-fuel welding and cutting.[10]
Uptake of oxygen from the air is the essential purpose of respiration, so oxygen supplementation is used in medicine. Oxygen therapy is used to treat emphysema, pneumonia, some heart disorders and any disease that impairs the body's ability to take up and use oxygen.[35] Treatments are flexible enough to be used in hospitals, the patient's home, or increasingly by portable devices. Oxygen tents were once commonly used in oxygen supplementation, but have since been mostly replaced by the use of oxygen masks or nasal cannulas. Hyperbaric medicine uses hyperbaric oxygen chambers to increase the partial pressure of oxygen around the patient and, when needed, the medical staff. Carbon monoxide poisoning, gas gangrene and decompression sickness (the "bends") are sometimes treated using these devices.[35][36]
People who climb mountains or fly in non-pressurized fixed-wing aircraft sometimes have supplemental oxygen supplies.[37] Passengers traveling in commercial airplanes have an emergency supply of oxygen automatically supplied to them in case of cabin depressurization. Sudden cabin pressure loss activates chemical oxygen generators above each seat, causing oxygen masks to drop and forcing iron fillings into the sodium chlorate inside the canister.[29] A steady stream of oxygen gas is produced by the exothermic reaction. A ValuJet airplane crashed after life-expired oxygen canisters, which were being shipped in the cargo hold, activated and burned a hole in the airplane. They were miss-labelled as empty; and were being carried in the hold in contravention of the Dangerous Goods regulations.[38]
A notable application of oxygen as a low-pressure breathing gas is in modern spacesuits, which surround their occupant's body with pressurized air. These devices use nearly pure oxygen at about one third normal pressure, resulting in a normal blood partial pressures of oxygen. This trade-off of higher oxygen concentration for lower pressure is needed to maintain flexible spacesuits.
Oxygen, as a supposed mild euphoric, has a history of recreational use (see oxygen bar). However, the reality of a pharmacological effect is doubtful, a placebo or psychological boost being the most plausible explanation.
In the 19th century, oxygen was often mixed with nitrous oxide to temper its analgesic effect. A stable 50% gaseous mixture (Entonox) is commonly used in medicine today as an analgesic. However, the common basic anesthetic mixture is 30% oxygen with 70% nitrous oxide; the pain-suppressing effects, obviously, are due to the nitrous oxide and not to oxygen.
Smelting of iron ore into steel consumes 55% of commercially produced oxygen.[29] In this process, oxygen is injected through a high-pressure lance into molten iron, which removes sulfur and carbon impurities. The reaction is exothermic, so the temperature increases to 1700 ° C.[29]
Another 25% of commercially produced oxygen is used by the chemical industry.[29] Ethylene is reacted with oxygen to create ethylene oxide, which in turn is converted into ethylene glycol; the primary feeder material used to manufacture a host of products, including antifreeze and polyester polymers (the precursors of many plastics and fabrics).[29]
Most of the remaining 20% of commercially produced oxygen is used in medical applications, metal cutting and welding, as an oxidizer in rocket fuel, and in water treatment.[29] Oxygen is used in oxyacetylene welding burning acetylene with oxygen to produce a very hot flame. In this process, metal up to 60 cm thick is first heated with a small oxy-acetylene flame and then quickly cut by a large stream of oxygen.[39][40] Rocket propulsion requires a fuel and an oxidizer. Larger rockets use liquid oxygen as their oxidizer, which is mixed and ignited with the fuel for propulsion.
Paleoclimatologists measure the ratio of oxygen-18 and oxygen-16 in the shells and skeletons of marine organisms to determine what the climate was like millions of years ago. During periods of lower global temperatures, sea water molecules that contain the lighter isotope, oxygen-16, evaporate at a slightly faster rate than water molecules containing the 12% heavier oxygen-18.[41] Snow and rain from that evaporated water tends to be enriched in oxygen-16 and the seawater left behind tends to be enriched in oxygen-18. Marine organisms then incorporate more oxygen-18 into their skeletons and shells than they would in a warmer climate.[41] Paleoclimatologists also directly measure this ratio in air trapped in ice core samples that are up to several hundreds of thousand years old.
Oxygen presents two spectrophotometric absorption bands peaking at the wavelengths 687 and 760 nanometers. Some scientists have proposed to use the measurement of the radiance coming from vegetation canopies in those oxygen bands to characterize plant health status from a satellite platform.[42] This is because in those bands, it is possible to discriminate the vegetation's reflectance from the vegetation's fluorescence, which is much weaker. The measurement presents several technical difficulties due to the low signal to noise ratio and due to the vegetation's architecture, but it has been proposed as a possibility to monitor the carbon cycle from satellites on a global scale.
Since there are no known ways but the presence of life for planetary atmospheres to maintain high concentrations of oxygen, these same absorption bands have been proposed as a way (when telescopes have improved significantly) to search planets of nearby stars spectrophotometrically for signs of life-as-we-know-it.
In almost all known compounds of oxygen, the oxidation state of oxygen is -2. In a few compounds such as peroxides, the oxidation state is -1. Other oxidation states are quite rare such as:-1/3 (ozonides), +1 (oxygen(I) fluoride) and +2 (oxygen fluoride). The most familiar oxygen-containing compound is H2O. Other well-known examples include silica (found in sand, glass, rock, etc.), and the compounds of carbon and oxygen, such as carbon dioxide (CO2), alcohols (R-OH), carbonyls, (R-CO-H or R-CO-R), and carboxylic acids (R-COOH). Oxygenated radicals such as chlorates (ClO3−), perchlorates (ClO4−), chromates (CrO42−), dichromates (Cr2O72−), permanganates (MnO4−), and nitrates (NO3−) are strong oxidizing agents in and of themselves. Phosphorus is biologically important in its oxygenated form as the phosphate (PO43−) ion. Many metals bond with oxygen atoms, such as iron in iron(III) oxide (Fe2O3), commonly called rust.
One unexpected oxygen compound is dioxygen hexafluoroplatinate O2+PtF6−. It was discovered when Neil Bartlett was studying the properties of platinum hexafluoride (PtF6).[43] He noticed a change in color when this compound was exposed to atmospheric air. Bartlett reasoned that xenon should be oxidized by PtF6. This led him to the discovery of xenon hexafluoroplatinate Xe+PtF6−.Epoxides are ethers in which the oxygen atom is part of a ring of three atoms. O22+ is another cation as in O2F2, it is only formed in the presence of stronger oxidants than oxygen, which limits this cation to oxygen fluorines, e.g. oxygen fluoride.[44]
When dissolved in water, many metallic oxides form alkaline solutions while many oxides of nonmetals form acidic solutions. For example, sodium oxide in solution forms the strong base sodium hydroxide while phosphorus pentoxide in solution forms phosphoric acid.[45]
Although oxygen molecules are not generally reactive at room temperature they do react with certain strong inorganic reducing substances, such as ferrous sulfate in aqueous solution.[45] Oxygen also reacts spontaneously with many organic compounds at or below room temperature in a process called autoxidation.[45] Other substances need to be heated before they will react with oxygen in bulk but some, such as iron, readily forms iron oxide, or rust.
Due to its electronegativity, oxygen forms chemical bonds with almost all other free elements at elevated temperatures to give corresponding oxides. The only elements known to escape the possibility of combination with oxygen are a few of the noble gases and fluorine. So-called noble metals (common examples: gold, platinum) resist direct chemical combination with oxygen, and substances like gold(III) oxide must be formed by an indirect route.
Peroxides retain some of oxygen's original molecular structure. White or light yellow sodium peroxide (Na2O2) is formed when metallic sodium (Na) is burned in oxygen. Each oxygen atom in it's peroxide ion may have a full octet of 4 pairs of electrons.[46] Superoxides are a class of compounds that are very similar to peroxides, but with just one unpaired electron for each pair of oxygen atoms.[46]. These compounds form from oxidation of alkali metals with larger ionic radii (K, Rb, Cs). For example, Potassium superoxide ( KO2) is an orange-yellow solid formed when potassium (K) reacts with oxygen.
Hydrogen peroxide (H2O2) can be produced by passing a volume of 96 to 98% hydrogen and 2 to 4% oxygen through an electric discharge.[45] A more commercially viable method is allow autoxidation of an organic intermediate; 2-ethylanthrahydroquinone dissolved in an organic solvent is oxidized to H2O2 and 2-ethylanthraquinone.[45] The 2-ethylanthraquinone is then reduced and recycled back into the process.
Most chemically combined oxygen is locked in a class of minerals called silicates (which in turn are the major component of rocks and clays). The basic structure of silicates consists of two parts; units of silicon surrounded by four oxygen anions in a tetrahedral arrangement and units of metal-oxygen polyhedra that contain metal cations (examples: aluminium, calcium, iron and sodium).[46] Both units are linked together by sharing oxygen anions, forming complex polymers in the process.
Water- soluble silicates in the form of Na4SiO4, Na2SiO3, and Na2Si2O5 are used as detergents and adhesives.[46] NaxSixOx with a higher ratio of SiO2 to Na2O has a greater molecular weight and a lower solubility. Silica is a crystalline polymer with the chemical formula (SiO2)n. Quartz is the mineral form of silica in nature and the most common deposits of quartz are in sand.
Most of the thousands of organic compounds that contain oxygen are not made by direct action of oxygen. Many of the compounds that are directly created by a reaction with oxygen are commercially important. Examples and the reactions that form them include:[47]
Acetone ((CH3)2CO) and phenol (C6H5OH) are used as feeder materials in the synthesis of many different substances. The cumene (C6H5-CH(CH3)2) in the below reaction is commonly derived from petroleum.
C6H5-CH(CH3)2 + O2 -> C6H5-COOH(CH3)2 -> (CH3)2CO + C6H5OH
Acetylene (C2H2) along with a mix of carbon monoxide, hydrogen and water are formed directly by the oxidation of natural gas in the below simplified equation.[48]
CH4 + C2H6 + O2 -> C2H2 + CO + 3H2 + H2O
Ethylene oxide (C2H4O) is used to make the antifreeze ethylene glycol.
C2H4 + 1/2 O2 -catalyst-> C2H4O
Peracetic acid (CH3(COOH)O) is the feeder material used to make various epoxy compounds.
CH3CHO + O2 -catalyst-> CH3(COOH)O
from the lungs of most animals
Parts of DNA are made of oxygen and the element is found in almost all molecules that are important to life. Molecular oxygen, O2, is essential for cellular respiration in all aerobic organisms. Almost all animals use hemoglobin in their blood to transport oxygen from their lungs to their tissues, but some, such as spiders and lobsters, use hemerythrin.[24] A liter of blood can dissolve 200 cc of oxygen gas, which is much more than water can dissolve.[24] The below description of oxygen uptake and use is typical for vertebrates.
Oxygen diffuses through membranes and into red blood cells after inhalation into the lungs. The Heme group of hemoglobin by now already has carbon dioxide in its active site, but releases it for exhalation when oxygen is present. After being carried in blood to a body tissue in need of oxygen, it is handed-off from the Heme group to monooxygenase, an enzyme that also has an active site with an atom of iron.[24] Monooxygenase uses oxygen to catalyze many oxidation reactions in the body. Oxygen is also used as an electron acceptor in mitochondria to generate chemical energy in the form of adenosine triphosphate (ATP) during oxidative phosphorylation. Carbon dioxide, one of the waste products produced, is released from the cell and into the blood, where it combines with empty Heme groups. Blood circulates back to the lungs and the process repeats.[49] On average, a oxygen atom is used in respiration once every 3,000 years.[12]
Reactive oxygen species are dangerous by-products that sometimes result from the use of oxygen in organisms. Important examples include; oxygen free radicals such as the highly dangerous superoxide O2-, and the less harmful hydrogen peroxide ( H2O2).[24] The body uses superoxide dismutase to reduce superoxide radicals to hydrogen peroxide. Glutathione peroxidase and similar enzymes, then convent the H2O2 to water and dioxygen.[24]
Parts of the immune system of higher organisms, however, create peroxide, superoxide and singlet oxygen to destroy invading microbes. Recently, singlet oxygen has been found to be a source of biologically-produced ozone: this reaction proceeds through an unusual compound dihydrogen trioxide, also known as trioxidane, (HOOOH) which is an antibody-catalyzed product of singlet oxygen and water. This compound in turn disproportionates to ozone and peroxide, providing two powerful antibacterials. The body's range of defense against all of these active oxidizing agents is hardly surprising, then, given their "deliberate" employment as antimicrobial agents in the immune response.[50]
Oxygen was almost nonexistent in earth's atmosphere before the evolution of water oxidation in photosynthetic bacteria. Free oxygen first appeared in significant quantities during the Paleoproterozoic era (between 2.5 billion years ago and 1.6 billion years ago) as a product of the metabolic action of early anaerobes (archaea and bacteria). These organisms developed the mechanism of oxygen evolution between 3.5 and 2.7 billion years ago. At first, the produced oxygen dissolved in the oceans and reacted with iron, creating banded iron formations. It started to gas out of the oxygen-saturated waters about 2.7 billion years ago as evident in the rusting of iron-rich terrestrial rocks starting around that time. The amount of oxygen in the atmosphere increased gradually at first and shot up rapidly around 2.2 to 1.7 billion years ago to about 10% of its present level.[51]
The development of an oxygen-rich atmosphere was one of the most important events in the history of life on earth. The presence of large amounts of dissolved and free oxygen in the oceans and atmosphere may have driven most of the anaerobic organisms then living to extinction during the oxygen catastrophe about 2.4 billion years ago. However, the high electronegativity of O2 creates a large potential energy drop for cellular respiration, thus enabling organisms using aerobic respiration to produce much more ATP than anaerobic organisms. This makes them so efficient that they have come to dominate earth's biosphere.[52] Photosynthesis and cellular respiration of oxygen allowed for the evolution of eukaryotic cells and ultimately complex multicellular organisms such as plants and animals.
The atmospheric abundance of free oxygen in later geological epochs and its gradual increase up to the present has been largely due to synthesis by photosynthetic organisms. Over the past 500 million years, oxygen levels fluctuated between 15 and 35% per volume. Towards the end of the Carboniferous era (coal age) about 300 million years ago, atmospheric oxygen levels reached a maximum of 35% by volume, allowing insects and amphibians with limiting respiratory systems to grow much larger than today's species. Today, oxygen is the second most common component of the earth's atmosphere (about 21% by volume) after nitrogen. Human activities, including the burning of 7 billion tonnes of fossil fuels each year have had very little effect on the amount of free oxygen in the atmosphere.[12]
Oxygen is the most common of all chemical elements on earth, being found in water, air, and most mineral and organic substances, including most compounds in the human body. It combines with almost all other elements, and is so reactive that it was given the Greek name ‘oxygen’, meaning acid-forming. However, most of the compounds it forms are not acids. Its chemical reactions usually form heat (as in the animal body) and sometimes light (as in candles).
It has always been known that animals cannot live without air, but in 1674 Mayow showed that only one part of the air, about one-fifth, is essential for life, and named it ‘vital air’. A hundred years later Priestley isolated this part, oxygen; Lavoisier purified oxygen and its properties began to be studied.
Atmospheric air contains 21% oxygen, at a pressure of about 150 mm Hg varying with barometric pressure and to a small extent with humidity. It enters the lungs during breathing and is absorbed into the blood passively by diffusion, combining with haemoglobin and being carried in the bloodstream to all parts of the body. There it is used to metabolize or ‘burn’ foodstuffs in the cells, especially fats and carbohydrates, providing heat and creating new chemical compounds, water, and the waste product carbon dioxide. Tissues and organs vary in the length of time they can survive without oxygen, according to their provision for anaerobic metabolism. The brain cannot survive without oxygen; the cessation of breathing will cause unconsciousness in a few minutes, and death soon afterwards. Other tissues such as skeletal muscle can continue to work for a limited time, when glycogen stores are broken down without oxygen to provide energy; lactic acid is a by-product that leaks into the blood and makes it more acid, but can be recycled into carbohydrate stores in the liver.
In quiet breathing at rest we absorb about 0.2-0.3 litres/min of oxygen (depending on body size), but in vigorous exercise this can go up to over 2 litres/min. This increase is accomplished by increased breathing (which supplies oxygen to the lungs at a greater rate), increased cardiac output and flow of blood to the muscles, and greater extraction of oxygen from the blood by the muscles. If the oxygen supply to the muscles is inadequate then the anaerobic threshold is passed and anaerobic metabolism takes place, with production of lactic acid. After the exercise additional oxygen is needed to convert the lactic acid back to glycogen, and breathing remains enhanced while the oxygen debt is repaid.
The supply of oxygen to the body depends not on the percentage in the air breathed but on its tension or pressure. At high altitude, say 5000 metres above sea level, the percentage of oxygen is still 21%, but because atmospheric pressure is halved, the oxygen pressure is half that at sea level — 75 mm Hg rather than 150 mm Hg. A person may as a result suffer from hypoxia — a lack of oxygen.
High oxygen pressures can be harmful and cause oxygen poisoning, including lung damage and brain dysfunction. In nature high oxygen pressures only exist in deep water diving, and mankind has not had to evolve ways of combating them. Once scientists had purified oxygen it became possible to administer it to patients; this has life-saving possibilities, but care has to be taken not to exceed the toxic level.
Some compounds rich in oxygen, such as the pollutant ozone (itself a molecular form of oxygen), and hydrogen peroxide, can react with cells to produce strongly reactive forms of oxygen. Superoxide anions and unstable oxygen free radicals (such as hydroxyl and hydroperoxy radicals) can be toxic to cells, by way of excess lipid peroxidation. These are implicated, for example, in damage following the restoration of blood flow (reperfusion) after the blockage which causes heart attacks or strokes, and in a variety of other disease processes. However the body does have inherent enzymatic defences against free radical accumulation, and there are antioxidants, such as uric acid, ascorbate, and glutathione, which can inactivate them. Free radicals are likely to contribute also to the ageing process: the very substance by which we live may itself limit our lifespan. Thus oxygen, like most good things, can be dangerous in excess.
Mankind evolved to live close to sea level. Climbing mountains (causing hypoxia) and deep-sea diving (causing nitrogen narcosis or oxygen poisoning) can both be dangerous, in the absence of the right precautions.
Oxygen is one of the basic chemical elements. In its most common form, oxygen is a colorless gas found in air. It is one of the life-sustaining elements on Earth and is needed by all animals. Oxygen is also used in many industrial, commercial, medical, and scientific applications. It is used in blast furnaces to make steel, and is an important component in the production of many synthetic chemicals, including ammonia, alcohols, and various plastics. Oxygen and acetylene are combusted together to provide the very high temperatures needed for welding and metal cutting. When oxygen is cooled below -297° F (-183° C), it becomes a pale blue liquid that is used as a rocket fuel.
Oxygen is one of the most abundant chemical elements on Earth. About one-half of the earth's crust is made up of chemical compounds containing oxygen, and a fifth of our atmosphere is oxygen gas. The human body is about two-thirds oxygen. Although oxygen has been present since the beginning of scientific investigation, it wasn't discovered and recognized as a separate element until 1774 when Joseph Priestley of England isolated it by heating mercuric oxide in an inverted test tube with the focused rays of the sun. Priestley described his discovery to the French scientist Antoine Lavoisier, who experimented further and determined that it was one of the two main components of air. Lavoisier named the new gas oxygen using the Greek words oxys, meaning sour or acid, and genes, meaning producing or forming, because he believed it was an essential part of all acids.
In 1895, Karl Paul Gottfried von Linde of Germany and William Hampson of England independently developed a process for lowering the temperature of air until it liquefied. By carefully distillation of the liquid air, the various component gases could be boiled off one at a time and captured. This process quickly became the principal source of high quality oxygen, nitrogen, and argon.
In 1901, compressed oxygen gas was burned with acetylene gas in the first demonstration of oxy-acetylene welding. This technique became a common industrial method of welding and cutting metals.
The first use of liquid rocket propellants came in 1923 when Robert Goddard of the United States developed a rocket engine using gasoline as the fuel and liquid oxygen as the oxidizer. In 1926, he successfully flew a small liquid-fueled rocket a distance of 184 ft (56 m) at a speed of about 60 mph (97 kph).
After World War II, new technologies brought significant improvements to the air separation process used to produce oxygen. Production volumes and purity levels increased while costs decreased. In 1991, over 470 billion cubic feet (13.4 billion cubic meters) of oxygen were produced in the United States, making it the second-largest-volume industrial gas in use.
Worldwide the five largest oxygen-producing areas are Western Europe, Russia (formerly the USSR), the United States, Eastern Europe, and Japan.
Raw Materials
Oxygen can be produced from a number of materials, using several different methods. The most common natural method is photo-synthesis, in which plants use sunlight convert carbon dioxide in the air into oxygen. This offsets the respiration process, in which animals convert oxygen in the air back into carbon dioxide.
The most common commercial method for producing oxygen is the separation of air using either a cryogenic distillation process or a vacuum swing adsorption process. Nitrogen and argon are also produced by separating them from air.
Oxygen can also be produced as the result of a chemical reaction in which oxygen is freed from a chemical compound and becomes a gas. This method is used to generate limited quantities of oxygen for life support on submarines, aircraft, and spacecraft.
Hydrogen and oxygen can be generated by passing an electric current through water and collecting the two gases as they bubble off. Hydrogen forms at the negative terminal and oxygen at the positive terminal. This method is called electrolysis and produces very pure hydrogen and oxygen. It uses a large amount of electrical energy, however, and is not economical for large-volume production.
The Manufacturing
Process
Most commercial oxygen is produced using a variation of the cryogenic distillation process originally developed in 1895. This process produces oxygen that is 99+% pure. More recently, the more energy-efficient vacuum swing adsorption process has been used for a limited number of applications that do not require oxygen with more than 90-93% purity.
Here are the steps used to produce commercial-grade oxygen from air using the cryogenic distillation process.
Pretreating
Because this process utilizes an extremely cold cryogenic section to separate the air, all impurities that might solidify—such as water vapor, carbon dioxide, and certain heavy hydrocarbons—must first be removed to prevent them from freezing and plugging the cryogenic piping.
* The air is compressed to about 94 psi (650 kPa or 6.5 atm) in a multi-stage compressor. It then passes through a water-cooled aftercooler to condense any water vapor, and the condensed water is removed in a water separator.
* The air passes through a molecular sieve adsorber. The adsorber contains zeolite and silica gel-type adsorbents, which trap the carbon dioxide, heavier hydrocarbons, and any remaining traces of water vapor. Periodically the adsorber is flushed clean to remove the trapped impurities. This usually requires two adsorbers operating in parallel, so that one can continue to process the air-flow while the other one is flushed.
Separating
Air is separated into its major components—nitrogen, oxygen, and argon—through a distillation process known as fractional distillation. Sometimes this name is shortened to fractionation, and the vertical structures used to perform this separation are called fractionating columns. In the fractional distillation process, the components are gradually separated in several stages. At each stage the level of concentration, or fraction, of each component is increased until the separation is complete.
Because all distillation processes work on the principle of boiling a liquid to separate one or more of the components, a cryogenic section is required to provide the very low temperatures needed to liquefy the gas components.
* The pretreated air stream is split. A small portion of the air is diverted through a compressor, where its pressure is boosted. It is then cooled and allowed to expand to nearly atmospheric pressure. This expansion rapidly cools the air, which is injected into the cryogenic section to provide the required cold temperatures for operation.
* The main stream of air passes through one side of a pair of plate fin heat exchangers operating in series, while very cold oxygen and nitrogen from the cryogenic section pass through the other side. The incoming air stream is cooled, while the oxygen and nitrogen are warmed. In some operations, the air may be cooled by passing it through an expansion valve instead of the second heat exchanger. In either case, the temperature of the air is lowered to the point where the oxygen, which has the highest boiling point, starts to liquefy.
* The air stream—now part liquid and part gas—enters the base of the high-pressure fractionating column. As the air works its way up the column, it loses additional heat. The oxygen continues to liquefy, forming an oxygen-rich mixture in the bottom of the column, while most of the nitrogen and argon flow to the top as a vapor.
* The liquid oxygen mixture, called crude liquid oxygen, is drawn out of the bottom of the lower fractionating column and is cooled further in the subcooler. Part of this stream is allowed to expand to nearly atmospheric pressure and is fed into the low-pressure fractionating column. As the crude liquid oxygen works its way down the column, most of the remaining nitrogen and argon separate, leaving 99.5% pure oxygen at the bottom of the column.
* Meanwhile, the nitrogen/argon vapor from the top of the high-pressure column is cooled further in the subcooler. The mixed vapor is allowed to expand to nearly atmospheric pressure and is fed into the top of the low-pressure fractionating column. The nitrogen, which has the lowest boiling point, turns to gas first and flows out the top of the column as 99.995% pure nitrogen.
* The argon, which has a boiling point between the oxygen and the nitrogen, remains a vapor and begins to sink as the nitrogen boils off. As the argon vapor reaches a point about two-thirds the way down the column, the argon concentration reaches its maximum of about 7-12% and is drawn off into a third fractionating column, where it is further recirculated and refined. The final product is a stream of crude argon containing 93-96% argon, 2-5% oxygen, and the balance nitrogen with traces of other gases.
Purifying
The oxygen at the bottom of the low-pressure column is about 99.5% pure. Newer cryogenic distillation units are designed to recover more of the argon from the low-pressure column, and this improves the oxygen purity to about 99.8%.
* If higher purity is needed, one or more additional fractionating columns may be added in conjunction with the low-pressure column to further refine the oxygen product. In some cases, the oxygen may also be passed over a catalyst to oxidize any hydrocarbons. This process produces carbon dioxide and water vapor, which are then captured and removed.
Distributing
About 80-90% of the oxygen produced in the United States is distributed to the end users in gas pipelines from nearby air separation plants. In some parts of the country, an extensive network of pipelines serves many end users over an area of hundred of miles (kilometers). The gas is compressed to about 500 psi (3.4 MPa or 34 atm) and flows through pipes that are 4-12 in (10-30 cm) in diameter. Most of the remaining oxygen is distributed in insulated tank trailers or railroad tank cars as liquid oxygen.
* If the oxygen is to be liquefied, this process is usually done within the low-pressure fractionating column of the air separation plant. Nitrogen from the top of the low-pressure column is compressed, cooled, and expanded to liquefy the nitrogen. This liquid nitrogen stream is then fed back into the low-pressure column to provide the additional cooling required to liquefy the oxygen as it sinks to the bottom of the column.
* Because liquid oxygen has a high boiling point, it boils off rapidly and is rarely shipped farther than 500 mi (800 km). It is transported in large, insulated tanks. The tank body is constructed of two shells and the air is evacuated between the inner and outer shell to retard heat loss. The vacuum space is filled with a semisolid insulating material to further halt heat flow from the outside.
Quality Control
The Compressed Gas Association establishes grading standards for both gaseous oxygen and liquid oxygen based on the amount and type of impurities present. Gas grades are called Type I and range from A, which is 99.0% pure, to F, which is 99.995% pure. Liquid grades are called Type II and also range from A to F, although the types and amounts of allowable impurities in liquid grades are different than in gas grades. Type I Grade B and Grade C and Type II Grade C are 99.5% pure and are the most commonly produced grades of oxygen. They are used in steel making and in the manufacture of synthetic chemicals.
The operation of cryogenic distillation airseparation units is monitored by automatic instruments and often uses computer controls. As a result, their output is consistent in quality. Periodic sampling and analysis of the final product ensures that the standards of purity are being met.
The Future
In January 1998, the United States launched the Lunar Prospector satellite into orbit around the moon. Among its many tasks, this satellite will be scanning the surface of the moon for indications of water. Scientists hope that if sufficient quantities of water are found, it could be used to produce hydrogen and oxygen gases through electrolysis, using solar power to generate the electricity. The hydrogen could be used as a fuel, and the oxygen could be used to provide life support for lunar colonies. Another plan involves extracting oxygen from chemical compounds in the lunar soil using a solar-powered furnace for heat.
STORM
Storm
An atmospheric disturbance involving perturbations of the prevailing pressure and wind fields on scales ranging from tornadoes (0.6 mi or 1 km across) to extratropical cyclones (1.2–1900 mi or 2–3000 km across); also, the associated weather (rain storm, blizzard, and the like). Storms influence human activity in such matters as agriculture, transportation, building construction, water impoundment and flood control, and the generation, transmission, and consumption of electric energy. See also Wind.
The form assumed by a storm depends on the nature of its environment, especially the large-scale flow patterns and the horizontal and vertical variation of temperature; thus the storms most characteristic of a given region vary according to latitude, physiographic features, and season. Extratropical cyclones and anticyclones are the chief disturbances over roughly half the Earth's surface. Their circulations control the embedded smaller-scale storms. Large-scale disturbances of the tropics differ fundamentally from those of extratropical latitudes. See also Hurricane; Squall; Tornado; Tropical meteorology.
Cyclones form mainly in close proximity to the jet stream, that is, in strongly baroclinic regions where there is a large increase of wind with height. Weather patterns in cyclones are highly variable, depending on moisture content and thermodynamic stability of air masses drawn into their circulations. Warm and occluded fronts, east of and extending into the cyclone center, are regions of gradual upgliding motions, with widespread cloud and precipitation but usually no pronounced concentration of stormy conditions. Extensive cloudiness also is often present in the warm sector. Passage of the cold front is marked by a sudden wind shift, often with the onset of gusty conditions, with a pronounced tendency for clearing because of general subsidence behind the front. Showers may be present in the cold air if it is moist and unstable because of heating from the surface. Thunderstorms, with accompanying squalls and heavy rain, are often set off by sudden lifting of warm, moist air at or near the cold front, and these frequently move eastward into the warm sector. See also Cyclone; Jet stream; Weather.
Extratropical cyclones alternate with high-pressure systems or anticyclones, whose circulation is generally opposite to that of the cyclone. The circulations of highs are not so intense as in well-developed cyclones, and winds are weak near their centers. In low levels the air spirals outward from a high; descent in upper levels results in warming and drying aloft. Anticyclones fall into two main categories, the warm “subtropical” and the cold “polar” highs.
Between the scales of ordinary air turbulence and of cyclones, there exist a variety of circulations over a middle-scale or mesoscale range, loosely defined as from about one-half up to a few hundred miles. Alternatively, these are sometimes referred to as subsynoptic-scale disturbances because their dimensions are so small that they elude adequate description by the ordinary synoptic network of surface weather stations.
Thus their detection often depends upon
According to the Bible, a giant storm sent by God flooded the Earth. Noah and his family and the animals entered the Ark, and "the same day were all the fountains of the great deep broken up, and the windows of heaven were opened, and the rain was upon the earth forty days and forty nights." The flood covered even the highest mountains to a depth of more than twenty feet, and all creatures died; only Noah and those with him on the Ark were left alive. See Noah's Ark for details.
In Greek mythology there were several gods of storms: Briareos, by himself the god of sea storms, Aigaios, a god of the violent sea storms and Aiolos who kept the storm-winds, squalls and tempests locked away in the hollows of the floating island of Aiolia, to be released at the command of the gods.
William Shakespeare's play The Tempest (1611) was based on the following incident.[6] Sir Thomas Gates, future governor of Virginia, was on his way to England from Jamestown, Virginia. On Saint James Day while between Cuba and the Bahamas a hurricane raged for nearly two days. Though one of the small vessels in the fleet sank to the bottom of the Florida Straits, seven of the remaining vessels reached Virginia within several days after the storm. The flagship of the fleet, known as Sea Adventure, disappeared and was presumed lost. A small bit of fortune befell the ship and her crew when they made landfall on Bermuda. The vessel was damaged on a surrounding coral reef, but all aboard survived for nearly a year on the island. The British colonists claimed the island and quickly settled Bermuda. In May 1610, they set forth for Jamestown, this time arriving at their destination.
The Ninth Wave is an 1850 painting by Ivan Aivazovsky.
The Ninth Wave is an 1850 painting by Ivan Aivazovsky.
The Romantic seascape painters J. M. W. Turner (1775-1851) and Ivan Aivazovsky (1817-1900) created some of the most lasting impressions of the sublime and stormy seas that are firmly imprinted on the popular mind. Turner's representations of powerful natural forces reinvented the traditional seascape during the first half of the nineteenth century. Upon his travels to Holland, he took note of the familiar large rolling waves of the English seashore transforming into the sharper, choppy waves of a Dutch storm. A characteristic example of Turner’s dramatic seascape is The Slave Ship (properly Slavers throwing overboard the Dead and Dying - Typhoon Coming On) of 1840. Aivazovsky left several thousand turbulent canvases in which he increasingly eliminated human figures and historical background to focus on such essential elements as light, sea, and sky. His grandiose Ninth Wave
The notion that great storms accompany the passing of great persons was formerly widespread and generally accepted. The most widely mentioned instance was probably the death of Cromwell in 1658, still remembered by Samuel Pepys in his Diary four years later on 18 February 1662, while the following year he was worried by another storm: (19 Oct. 1663): Waked with a very highe winde, and said to my wife, ‘I pray God I hear not of the death of any great person, this wind is so high’, fearing that the Queene might be dead.
It could apparently be the great evil of the deceased or their great fame which caused the disturbance (Denham Tracts, 1895: ii. 29-30). On the other side of the coin, several references in Opie and Tatem (1989: 432-3) indicate that good people's deeds are often accompanied by good weather.storm, disturbance of the ordinary conditions of the atmosphere attended by wind, rain, snow, sleet, hail, or thunder and lightning. Types of storms include the extratropical cyclone, the common, large-scale storm of temperate latitudes; the tropical cyclone, or hurricane, which is somewhat smaller in area than the former and accompanied by high winds and heavy rains; the tornado, or “twister,” a small but intense storm with very high winds, usually of limited duration; and the thunderstorm, local in nature and accompanied by brief but heavy rain showers and often by hail. The term storm is also applied to blizzards, sandstorms, and dust storms, in which high wind is the dominant meteorological element. A storm surge, sometimes called a tidal wave, is a flood of ocean or lake water that occurs in areas subject to tropical storms and bordering on shallow waters, but any strong low-pressure system in a coastal area, such as a northeaster along the Atlantic coast of North America, may produce a storm surge. Storm surges are due mostly to wind, which pushes the water ahead of a storm. In Galveston, Tex., in 1900 a hurricane with a wind velocity of more than 100 mi (160 km) per hr caused an ocean storm surge 15 ft (5 m) above normal high tide levels that flooded coastal areas, resulting in the loss of thousands of lives and extensive property damage. The highest storm surge on record in the United States is that caused by Hurricane Katrina (2005), which had sustained winds at landfall in SE Louisiana of more than 140 mi (225 km) per hr and a storm surge that by one estimate reached 29 ft (8.8 m) on the SW Mississippi coast and caused coastal devastation from
Storm chasing is broadly defined as the pursuit of any severe weather condition, regardless of motive. A person who chases storms is known as a storm chaser, or simply a chaser. While witnessing a tornado is the biggest objective for many chasers, many chase thunderstorms and delight in seeing cumulonimbus structure, watching a barrage of hail and lightning, and seeing what skyscapes unfold. There are also a smaller number of storm chasers who chase hurricanes.
Storm chasing is chiefly a recreational endeavor, with motives usually given toward photographing the storm for personal reasons. Though scientific work is sometimes cited as a goal, such work is almost always impractical except for those participating in a university or government project.[1] Many chasers also are storm spotters, reporting their observations of hazardous weather to the authorities. Storm chasers are not paid to chase, with the exception of television media crews in certain television markets, video stringers and photographers, and a handful of graduate meteorologists and professors. A few entrepreneurs, however, manage to sell storm video and pictures or operate "chase tour" services. Financial returns are relatively meager given the expenses with most chasers spending more than they take in. No degree or certification is required to be a storm chaser. The NWS (National Weather Service) puts on severe weather workshops and storm spotter training.
The term "storm chaser" is also loosely applied to any of the support personnel (insurance staff, contractors, etc.) brought in to clean up after large storms.
The very first storm chaser is generally agreed to be Roger Jensen (1933–2001), a Fargo, North Dakota native who pursued western Minnesota storms from Lake Park around 1953 ([1] [2]). David Hoadley (1938– ) began chasing North Dakota storms in 1956, systematically using data from area weather offices. Bringing research chasing to the forefront was Neil Ward (1913–1972) who in the 1950s and 1960s enlisted the help of Oklahoma state police to study storms. His work pioneered modern storm spotting and made institutional chasing a reality.
In 1972 the University of Oklahoma in cooperation with the National Severe Storms Laboratory began the Tornado Intercept Project. This was the first large-scale chase activity sponsored by an institution. It culminated in a brilliant success in 1973, with the Union City, Oklahoma tornado providing a foundation for tornado morphology.[2] The project produced the first legion of veteran storm chasers, with Hoadley's Storm Track magazine bringing the community together in 1977. Storm chasing then reached popular culture in three major spurts: in 1978 with the broadcast of a segment on the television program In Search Of; in 1985 with a documentary on the PBS series Nova; and in May 1996 with the theatrical release of Twister which provided an action-packed but comically distorted glimpse at the hobby. Further early exposure to storm chasing encouraging some in the weather community resulted from several articles beginning in the late 1970s in Weatherwise magazine. Various television programs, increased coverage of severe weather by the media, and the Internet have also contributed to a significant growth of storm chasing since the mid-late 1990s. A sharp increase in the general public impulsively wandering in their local area searching for tornadoes is likewise largely attributable to these factors.
Chasing often involves driving thousands of miles in order to witness the relatively short window of time of active severe thunderstorms. It is not uncommon for a storm chaser to end up empty handed on any particular day. Storm chasers' degrees of involvement, philosophies, and techniques vary widely, but many chasers spend a significant amount of time forecasting both before going on the road as well as during the chase using a variety of sources for weather data. Most storm chasers are not meteorologists, and many chasers expend significant time and effort in learning meteorology and the intricacies of severe convective storm prediction through both study and experience.
There are inherent dangers involved in storm chasing. They range from lightning, tornadoes, large hail, flooding, hazardous road conditions (rain or hail-covered roadways), animals on the roadway, reduced visibility from heavy rain (often wind blown), and hail fog. Most directly weather-related hazards such as from a tornado are minimal, if the storm chaser is knowledgeable and cautious. Lightning, however, is an unavoidable hazard. The most significant hazard actually is driving, which, in itself, is a statistically dangerous activity that is exacerbated by the severe weather. Adding still more to this hazard are the copious distractions that can be vying for a chasers' attention: driving, communicating to chase partners and to others with a phone or radio, navigating, watching the sky, checking weather data, and shooting photos or video. Again here, caution is paramount in minimizing the risk. Chasers try to prevent the driver from multi-tasking either with chase partners covering the other aspects or the driver pulling over to do these other things if he/she is chasing alone. Many people also think that anybody can chase tornadoes, and copy the movie Twister, so they should remember that the dangers of chasing are real, and not go chasing unless experienced, or with experienced chasers. STROMS ARE SCARY!
Storm chasers are most active in May and June across the Great Plains of the United States (and Canada), with perhaps a couple hundred individuals active on any given day. Some organized chasing efforts have also begun in southeast Australia, with the biggest successes in November and December. A handful of individuals are also known to be chasing in other countries, including Israel, Italy, Spain, France, Belgium, Germany, Finland, the Netherlands, Switzerland and New Zealand; though many people trek to the Great Plains of North America from these and other countries around the world (especially the United Kingdom).
Most storm chasers will vary with regards to the amount of equipment used, some prefer a minimalist approach where only basic photographic equipment is taken on a chase while others use everything from satellite based tracking systems and live data feeds to vehicle mounted weather stations.
Top of a NSSL chase vehicle showing A/C unit, compass, and Global Positioning System.
Top of a NSSL chase vehicle showing A/C unit, compass, and Global Positioning System.
Historically, storm chasing relied on either in field analysis or now-casts from trained observers. The first in-field technology consisted of radio gear for communication. Much of this equipment could also be adapted to receive radiofax data which was useful for receiving basic observational and analysis data. The primary users of such technology were university research groups who often had larger budgets than individual chasers. Radio scanners were also heavily used to listen in on emergency services and storm spotters so as to determine where the most active or dangerous weather was located. It was not until the end of the 1980s that the evolution of the laptop computer would revolutionize storm chasing.
With the development of the mobile computers the first in computer mapping software was made available, at about the same time the VHS camcorder began to grow in popularity rapidly. Prior to the late 1980s most motion picture equipment consisted of 8mm film cameras. While the quality of the first VHS consumer cameras was quite poor when compared to traditional film formats the amount of video which could be shot with a minimal amount of resources was much greater than any film format at the time.
The 1990s marked the first technological leaps and bounds. With the quick development of solid state technology, television sets for example could be installed in most vehicles with ease allowing storm chasers to actively view local TV stations. Mobile phones became popular making group coordination easier when traditional radio communications methods were not adequate. The development of the public internet in 1993 allowed FTP access to some of the first university weather sites. The mid 1990's marked the development of smaller more efficient marine radars. While such marine radars are illegal if used in land-mobile situations many chasers were quick to adopt them in an effort to have mobile radar.[3] The first personal lightning detection and mapping devices also became available[4] and the first online radar data was also offered by private corporations often with a delay for free services. A major turning point was the advent of civilian GPS in 1996, at first GPS units were very costly and only offered basic functions but that would soon change. Towards the late 1990s the internet was awash in weather data and free weather software, the first true cellular internet modems for consumer use also emerged providing chasers access to data in the field without having to rely on a nowcaster. The NWS also released the first free, up to date Nexrad Level 3 radar data. In conjunction with all this, GPS units now had the ability to connect with computers, allowing greater ease when navigating.
2001 marked the next great technological leap for storm chasers as the first wi-fi units began to emerge offering wireless broadband service in many cases for free. In 2002, the first windows-based package to combine GPS positioning and Doppler Radar appeared called SWIFT WX[5]. SWIFT WX allowed storm chasers to accurately position themselves relative to tornadic storms while mobile. In 2004 two more storm chaser tools emerged. The first was a new XM satellite radio based system utilizing a special receiver and Baron Weather software.[6] Unlike pre-existing cellular based services there was no risk of dead spots and that meant even in the most remote areas storm chasers still had a live data feed. The second tool was a new piece of software called Grlevel3.[7] Grlevel3 utilized both free and subscripted based raw weather radar files displaying the data in a true vector format.
The most common chaser communications device is the cellular phone. Storm chasers often travel in small groups of cars, and use Citizen Band radios (declining in use) and inexpensiveGMRS/FRS hand-held transceivers (increasing in popularity) for inter-car communication. Many chasers are also amateur radio operators and sometimes use the 2 meter VHF and 70cm UHF bands to communicate between vehicles or with SKYWARN spotter networks. Scanners are often used to monitor spotter and sometimes public safety communications.
Many storm chasers have also adapted the use of laptops in conjunction with GPS receivers and laptop desks for travel directions and data collection
A increasingly common storm chaser practice is to borrow 2.4 GHz WIFI which may emanate from a commercial provider, public source or private source. Storm chasers also use high-speed internet access available in any library, even in the smallest towns in the US. Other means of live data acquisition include the use of Baron WeatherWorx ThreatNet System via XM radio's satellite (coupled with a GPS unit), or by the use of cellular internet service where one's cell phone may act as a network interface when connected to a computer system.
In-field environmental data is still popular among some storm chasers, especially temperature, humidity and wind speed data. Many have chosen to mount weather stations made by Davis Instruments Corp atop their vehicles.
An atmospheric disturbance involving perturbations of the prevailing pressure and wind fields on scales ranging from tornadoes (0.6 mi or 1 km across) to extratropical cyclones (1.2–1900 mi or 2–3000 km across); also, the associated weather (rain storm, blizzard, and the like). Storms influence human activity in such matters as agriculture, transportation, building construction, water impoundment and flood control, and the generation, transmission, and consumption of electric energy. See also Wind.
The form assumed by a storm depends on the nature of its environment, especially the large-scale flow patterns and the horizontal and vertical variation of temperature; thus the storms most characteristic of a given region vary according to latitude, physiographic features, and season. Extratropical cyclones and anticyclones are the chief disturbances over roughly half the Earth's surface. Their circulations control the embedded smaller-scale storms. Large-scale disturbances of the tropics differ fundamentally from those of extratropical latitudes. See also Hurricane; Squall; Tornado; Tropical meteorology.
Cyclones form mainly in close proximity to the jet stream, that is, in strongly baroclinic regions where there is a large increase of wind with height. Weather patterns in cyclones are highly variable, depending on moisture content and thermodynamic stability of air masses drawn into their circulations. Warm and occluded fronts, east of and extending into the cyclone center, are regions of gradual upgliding motions, with widespread cloud and precipitation but usually no pronounced concentration of stormy conditions. Extensive cloudiness also is often present in the warm sector. Passage of the cold front is marked by a sudden wind shift, often with the onset of gusty conditions, with a pronounced tendency for clearing because of general subsidence behind the front. Showers may be present in the cold air if it is moist and unstable because of heating from the surface. Thunderstorms, with accompanying squalls and heavy rain, are often set off by sudden lifting of warm, moist air at or near the cold front, and these frequently move eastward into the warm sector. See also Cyclone; Jet stream; Weather.
Extratropical cyclones alternate with high-pressure systems or anticyclones, whose circulation is generally opposite to that of the cyclone. The circulations of highs are not so intense as in well-developed cyclones, and winds are weak near their centers. In low levels the air spirals outward from a high; descent in upper levels results in warming and drying aloft. Anticyclones fall into two main categories, the warm “subtropical” and the cold “polar” highs.
Between the scales of ordinary air turbulence and of cyclones, there exist a variety of circulations over a middle-scale or mesoscale range, loosely defined as from about one-half up to a few hundred miles. Alternatively, these are sometimes referred to as subsynoptic-scale disturbances because their dimensions are so small that they elude adequate description by the ordinary synoptic network of surface weather stations.
Thus their detection often depends upon
According to the Bible, a giant storm sent by God flooded the Earth. Noah and his family and the animals entered the Ark, and "the same day were all the fountains of the great deep broken up, and the windows of heaven were opened, and the rain was upon the earth forty days and forty nights." The flood covered even the highest mountains to a depth of more than twenty feet, and all creatures died; only Noah and those with him on the Ark were left alive. See Noah's Ark for details.
In Greek mythology there were several gods of storms: Briareos, by himself the god of sea storms, Aigaios, a god of the violent sea storms and Aiolos who kept the storm-winds, squalls and tempests locked away in the hollows of the floating island of Aiolia, to be released at the command of the gods.
William Shakespeare's play The Tempest (1611) was based on the following incident.[6] Sir Thomas Gates, future governor of Virginia, was on his way to England from Jamestown, Virginia. On Saint James Day while between Cuba and the Bahamas a hurricane raged for nearly two days. Though one of the small vessels in the fleet sank to the bottom of the Florida Straits, seven of the remaining vessels reached Virginia within several days after the storm. The flagship of the fleet, known as Sea Adventure, disappeared and was presumed lost. A small bit of fortune befell the ship and her crew when they made landfall on Bermuda. The vessel was damaged on a surrounding coral reef, but all aboard survived for nearly a year on the island. The British colonists claimed the island and quickly settled Bermuda. In May 1610, they set forth for Jamestown, this time arriving at their destination.
The Ninth Wave is an 1850 painting by Ivan Aivazovsky.
The Ninth Wave is an 1850 painting by Ivan Aivazovsky.
The Romantic seascape painters J. M. W. Turner (1775-1851) and Ivan Aivazovsky (1817-1900) created some of the most lasting impressions of the sublime and stormy seas that are firmly imprinted on the popular mind. Turner's representations of powerful natural forces reinvented the traditional seascape during the first half of the nineteenth century. Upon his travels to Holland, he took note of the familiar large rolling waves of the English seashore transforming into the sharper, choppy waves of a Dutch storm. A characteristic example of Turner’s dramatic seascape is The Slave Ship (properly Slavers throwing overboard the Dead and Dying - Typhoon Coming On) of 1840. Aivazovsky left several thousand turbulent canvases in which he increasingly eliminated human figures and historical background to focus on such essential elements as light, sea, and sky. His grandiose Ninth Wave
The notion that great storms accompany the passing of great persons was formerly widespread and generally accepted. The most widely mentioned instance was probably the death of Cromwell in 1658, still remembered by Samuel Pepys in his Diary four years later on 18 February 1662, while the following year he was worried by another storm: (19 Oct. 1663): Waked with a very highe winde, and said to my wife, ‘I pray God I hear not of the death of any great person, this wind is so high’, fearing that the Queene might be dead.
It could apparently be the great evil of the deceased or their great fame which caused the disturbance (Denham Tracts, 1895: ii. 29-30). On the other side of the coin, several references in Opie and Tatem (1989: 432-3) indicate that good people's deeds are often accompanied by good weather.storm, disturbance of the ordinary conditions of the atmosphere attended by wind, rain, snow, sleet, hail, or thunder and lightning. Types of storms include the extratropical cyclone, the common, large-scale storm of temperate latitudes; the tropical cyclone, or hurricane, which is somewhat smaller in area than the former and accompanied by high winds and heavy rains; the tornado, or “twister,” a small but intense storm with very high winds, usually of limited duration; and the thunderstorm, local in nature and accompanied by brief but heavy rain showers and often by hail. The term storm is also applied to blizzards, sandstorms, and dust storms, in which high wind is the dominant meteorological element. A storm surge, sometimes called a tidal wave, is a flood of ocean or lake water that occurs in areas subject to tropical storms and bordering on shallow waters, but any strong low-pressure system in a coastal area, such as a northeaster along the Atlantic coast of North America, may produce a storm surge. Storm surges are due mostly to wind, which pushes the water ahead of a storm. In Galveston, Tex., in 1900 a hurricane with a wind velocity of more than 100 mi (160 km) per hr caused an ocean storm surge 15 ft (5 m) above normal high tide levels that flooded coastal areas, resulting in the loss of thousands of lives and extensive property damage. The highest storm surge on record in the United States is that caused by Hurricane Katrina (2005), which had sustained winds at landfall in SE Louisiana of more than 140 mi (225 km) per hr and a storm surge that by one estimate reached 29 ft (8.8 m) on the SW Mississippi coast and caused coastal devastation from
Storm chasing is broadly defined as the pursuit of any severe weather condition, regardless of motive. A person who chases storms is known as a storm chaser, or simply a chaser. While witnessing a tornado is the biggest objective for many chasers, many chase thunderstorms and delight in seeing cumulonimbus structure, watching a barrage of hail and lightning, and seeing what skyscapes unfold. There are also a smaller number of storm chasers who chase hurricanes.
Storm chasing is chiefly a recreational endeavor, with motives usually given toward photographing the storm for personal reasons. Though scientific work is sometimes cited as a goal, such work is almost always impractical except for those participating in a university or government project.[1] Many chasers also are storm spotters, reporting their observations of hazardous weather to the authorities. Storm chasers are not paid to chase, with the exception of television media crews in certain television markets, video stringers and photographers, and a handful of graduate meteorologists and professors. A few entrepreneurs, however, manage to sell storm video and pictures or operate "chase tour" services. Financial returns are relatively meager given the expenses with most chasers spending more than they take in. No degree or certification is required to be a storm chaser. The NWS (National Weather Service) puts on severe weather workshops and storm spotter training.
The term "storm chaser" is also loosely applied to any of the support personnel (insurance staff, contractors, etc.) brought in to clean up after large storms.
The very first storm chaser is generally agreed to be Roger Jensen (1933–2001), a Fargo, North Dakota native who pursued western Minnesota storms from Lake Park around 1953 ([1] [2]). David Hoadley (1938– ) began chasing North Dakota storms in 1956, systematically using data from area weather offices. Bringing research chasing to the forefront was Neil Ward (1913–1972) who in the 1950s and 1960s enlisted the help of Oklahoma state police to study storms. His work pioneered modern storm spotting and made institutional chasing a reality.
In 1972 the University of Oklahoma in cooperation with the National Severe Storms Laboratory began the Tornado Intercept Project. This was the first large-scale chase activity sponsored by an institution. It culminated in a brilliant success in 1973, with the Union City, Oklahoma tornado providing a foundation for tornado morphology.[2] The project produced the first legion of veteran storm chasers, with Hoadley's Storm Track magazine bringing the community together in 1977. Storm chasing then reached popular culture in three major spurts: in 1978 with the broadcast of a segment on the television program In Search Of; in 1985 with a documentary on the PBS series Nova; and in May 1996 with the theatrical release of Twister which provided an action-packed but comically distorted glimpse at the hobby. Further early exposure to storm chasing encouraging some in the weather community resulted from several articles beginning in the late 1970s in Weatherwise magazine. Various television programs, increased coverage of severe weather by the media, and the Internet have also contributed to a significant growth of storm chasing since the mid-late 1990s. A sharp increase in the general public impulsively wandering in their local area searching for tornadoes is likewise largely attributable to these factors.
Chasing often involves driving thousands of miles in order to witness the relatively short window of time of active severe thunderstorms. It is not uncommon for a storm chaser to end up empty handed on any particular day. Storm chasers' degrees of involvement, philosophies, and techniques vary widely, but many chasers spend a significant amount of time forecasting both before going on the road as well as during the chase using a variety of sources for weather data. Most storm chasers are not meteorologists, and many chasers expend significant time and effort in learning meteorology and the intricacies of severe convective storm prediction through both study and experience.
There are inherent dangers involved in storm chasing. They range from lightning, tornadoes, large hail, flooding, hazardous road conditions (rain or hail-covered roadways), animals on the roadway, reduced visibility from heavy rain (often wind blown), and hail fog. Most directly weather-related hazards such as from a tornado are minimal, if the storm chaser is knowledgeable and cautious. Lightning, however, is an unavoidable hazard. The most significant hazard actually is driving, which, in itself, is a statistically dangerous activity that is exacerbated by the severe weather. Adding still more to this hazard are the copious distractions that can be vying for a chasers' attention: driving, communicating to chase partners and to others with a phone or radio, navigating, watching the sky, checking weather data, and shooting photos or video. Again here, caution is paramount in minimizing the risk. Chasers try to prevent the driver from multi-tasking either with chase partners covering the other aspects or the driver pulling over to do these other things if he/she is chasing alone. Many people also think that anybody can chase tornadoes, and copy the movie Twister, so they should remember that the dangers of chasing are real, and not go chasing unless experienced, or with experienced chasers. STROMS ARE SCARY!
Storm chasers are most active in May and June across the Great Plains of the United States (and Canada), with perhaps a couple hundred individuals active on any given day. Some organized chasing efforts have also begun in southeast Australia, with the biggest successes in November and December. A handful of individuals are also known to be chasing in other countries, including Israel, Italy, Spain, France, Belgium, Germany, Finland, the Netherlands, Switzerland and New Zealand; though many people trek to the Great Plains of North America from these and other countries around the world (especially the United Kingdom).
Most storm chasers will vary with regards to the amount of equipment used, some prefer a minimalist approach where only basic photographic equipment is taken on a chase while others use everything from satellite based tracking systems and live data feeds to vehicle mounted weather stations.
Top of a NSSL chase vehicle showing A/C unit, compass, and Global Positioning System.
Top of a NSSL chase vehicle showing A/C unit, compass, and Global Positioning System.
Historically, storm chasing relied on either in field analysis or now-casts from trained observers. The first in-field technology consisted of radio gear for communication. Much of this equipment could also be adapted to receive radiofax data which was useful for receiving basic observational and analysis data. The primary users of such technology were university research groups who often had larger budgets than individual chasers. Radio scanners were also heavily used to listen in on emergency services and storm spotters so as to determine where the most active or dangerous weather was located. It was not until the end of the 1980s that the evolution of the laptop computer would revolutionize storm chasing.
With the development of the mobile computers the first in computer mapping software was made available, at about the same time the VHS camcorder began to grow in popularity rapidly. Prior to the late 1980s most motion picture equipment consisted of 8mm film cameras. While the quality of the first VHS consumer cameras was quite poor when compared to traditional film formats the amount of video which could be shot with a minimal amount of resources was much greater than any film format at the time.
The 1990s marked the first technological leaps and bounds. With the quick development of solid state technology, television sets for example could be installed in most vehicles with ease allowing storm chasers to actively view local TV stations. Mobile phones became popular making group coordination easier when traditional radio communications methods were not adequate. The development of the public internet in 1993 allowed FTP access to some of the first university weather sites. The mid 1990's marked the development of smaller more efficient marine radars. While such marine radars are illegal if used in land-mobile situations many chasers were quick to adopt them in an effort to have mobile radar.[3] The first personal lightning detection and mapping devices also became available[4] and the first online radar data was also offered by private corporations often with a delay for free services. A major turning point was the advent of civilian GPS in 1996, at first GPS units were very costly and only offered basic functions but that would soon change. Towards the late 1990s the internet was awash in weather data and free weather software, the first true cellular internet modems for consumer use also emerged providing chasers access to data in the field without having to rely on a nowcaster. The NWS also released the first free, up to date Nexrad Level 3 radar data. In conjunction with all this, GPS units now had the ability to connect with computers, allowing greater ease when navigating.
2001 marked the next great technological leap for storm chasers as the first wi-fi units began to emerge offering wireless broadband service in many cases for free. In 2002, the first windows-based package to combine GPS positioning and Doppler Radar appeared called SWIFT WX[5]. SWIFT WX allowed storm chasers to accurately position themselves relative to tornadic storms while mobile. In 2004 two more storm chaser tools emerged. The first was a new XM satellite radio based system utilizing a special receiver and Baron Weather software.[6] Unlike pre-existing cellular based services there was no risk of dead spots and that meant even in the most remote areas storm chasers still had a live data feed. The second tool was a new piece of software called Grlevel3.[7] Grlevel3 utilized both free and subscripted based raw weather radar files displaying the data in a true vector format.
The most common chaser communications device is the cellular phone. Storm chasers often travel in small groups of cars, and use Citizen Band radios (declining in use) and inexpensiveGMRS/FRS hand-held transceivers (increasing in popularity) for inter-car communication. Many chasers are also amateur radio operators and sometimes use the 2 meter VHF and 70cm UHF bands to communicate between vehicles or with SKYWARN spotter networks. Scanners are often used to monitor spotter and sometimes public safety communications.
Many storm chasers have also adapted the use of laptops in conjunction with GPS receivers and laptop desks for travel directions and data collection
A increasingly common storm chaser practice is to borrow 2.4 GHz WIFI which may emanate from a commercial provider, public source or private source. Storm chasers also use high-speed internet access available in any library, even in the smallest towns in the US. Other means of live data acquisition include the use of Baron WeatherWorx ThreatNet System via XM radio's satellite (coupled with a GPS unit), or by the use of cellular internet service where one's cell phone may act as a network interface when connected to a computer system.
In-field environmental data is still popular among some storm chasers, especially temperature, humidity and wind speed data. Many have chosen to mount weather stations made by Davis Instruments Corp atop their vehicles.
TELEPHONE
Telephone, device for communicating sound, especially speech, usually by means of wires in an electric circuit. The telephones now in general use evolved from the device invented by Alexander Graham Bell and patented by him in 1876 and 1877. Although Bell is recognized as the inventor, his telephone was preceded by many attempts to produce such an instrument. The principles on which it is based, and effective model instruments, were developed by different men at so nearly the same time that there are disputes about priority. In Bell's instrument, an electric current varied in intensity and frequency in accordance with sound waves. The sound waves caused a thin plate of soft iron, called the diaphragm, to vibrate. The vibrations disturbed the magnetic field of a bar magnet placed near the diaphragm, and this disturbance induced an electric current in a wire wound about the magnet. That current, when transmitted to a distant identical instrument, caused the diaphragm in it to vibrate, reproducing the original sound. Bell's instrument was thus both transmitter and receiver. The first notable improvement of the Bell telephone differentiated the transmitting instrument from the receiving instrument. Many other inventions have improved the telephone.
The switches used to route telephone calls, which were once electromechanical, are now largely replaced by sophisticated digital electronic switching systems. The electronic switches are much more flexible because they can be programmed to provide new services. The latest generation of switches have made a number of new features possible. Users, for example, can read the telephone number of the calling party on a display device if they choose to subscribe to a “caller ID” service. In “call waiting,” audio signals let a person already on a telephone know that someone else is trying to reach that person. Subscribers can also program the telephone switches to forward their calls automatically to another number (“call forwarding”). Other features include voice mailboxes and the ability to make three-way conference calls.
The problems associated with long-distance and intercity telephone service have been met with increasing success. The telephone lines used include the ordinary open wire lines, lead-sheathed cables consisting of many lines, and coaxial and fiber-optic cables. Coaxial and fiber-optic cables are typically placed underground, but other cables may be either overhead or underground. Transmission of telephone messages over long distances is often accomplished by means of radio and microwave transmissions. In some cases microwaves are sent to an orbiting communications satellite (see satellite, artificial) from which they are relayed back to a distant point on the earth. Cellular telephone systems allow small, low-power portable radio transceivers access to the telephone network; some cellular models provide access to the Internet. The incorporation of microelectronics and digital technology has led to the inclusion of unrelated applications in telephones, such as alarm clocks, calculators, and voice memos for recording short verbal reminders. A camera phone is a cellular phone that has photo taking and sending (to another camera phone or computer) capability. Similarly, a videophone transmits and receives real-time video images.
With the advent of the Internet, computer programs have been developed that allow voice communications across long distances, bypassing conventional carriers. The programs, which often require a computer equipped with a telephone or cable modem, microphone, and speakers, compress the voice message into digital signals. In other cases, a special adapter is used to allow a standard telephone to access the Internet directly though a cable modem or other broadband connection, or an Internet telephone (IP phone) may be used instead. The digital signals may be transmitted over the Internet to another computer, which must have another copy of the same program, or to a telephone. If a connection is established with another computer, the second program decompresses the digital signals and plays the sound almost instantaneously. The advantage of using the Internet is that under current tariffs no long-distance charges accrue on a computer to computer call, regardless of the length of the conversation. The disadvantages are the inferior sound quality on dialup connections and, in some cases, the need to have computers that are running the same program and the need to establish a connection between those
In 1984 a federal court ordered American Telephone and Telegraph Company (AT&T) to divest its Bell Telephone operating companies (the “Baby Bells”) after the court ruled that AT&T held a monopoly over U.S. telephone service. Since then, the regional operating companies and new competitors for long-distance service have grown through acquisitions and mergers. By 2007, AT&T (formerly SBC Communications, a Baby Bell, which acquired AT&T and adopted the name, and then merged in 2006 with Bell South, another Baby Bell) was the largest U.S. long-distance provider, followed by Verizon Communications (a Baby Bell that merged with MCI), and Sprint. Meanwhile, the seven Baby Bells that had been formed in 1984 were reduced to three, AT&T, Verizon, and Qwest Communications International. The distinctions between types of telephone providers, which had been created by the AT&T breakup, had disappeared, with telephone companies offering local and long-distance service in various locations, and owning wireless carriers and offering high-speed Internet service as well. At the same time these companies were also facing increasing challenges from cable television companies that offered Internet-based (VoIP) phone service over a broadband connection and independent VoIP companies, such as Vonage and Skype
Signalling began in an appropriately primitive manner. The user alerted the other end, or the exchange operator, by whistling into the transmitter. Exchange operation soon resulted in telephones being equipped with a bell, first operated over a second wire and later with the same wire using a condenser. Telephones connected to the earliest Strowger automatic exchanges had seven wires, one for the knife switch, one for each telegraph key, one for the bell, one for the push button and two for speaking.
After the 1930s, the base also enclosed the bell and induction coil, obviating the old separate bell box. Power was supplied to each subscriber line by central office batteries instead of a local battery, which required periodic service. For the next half century, the network behind the telephone became progressively larger and much more efficient, but after the dial was added the instrument itself changed little until touch tone replaced the dial in the 1960s.
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