2014 Version

Atmospheric Chemistry Glossary

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Tectonic Activity - The process of the formation, movement, interaction, and destruction of parts of the earth's crust on a generally large scale. This can be used to explain seismicity, volcanism, and mountain building. In spring 2011, the 9.0 magnitude earthquake off the coast of Japan (The Great East or Tohoku earthquake) moved the crust 2.4 meters. [Geology; v21; 2127-30; 1993.] [Journal of Oil and Gas; v92; 86-93; 1994.] [Science; v277; 1177; 1997; DOI:10.1126/science.277.5330.1177b] [Science; v310; 1914 - 1915; 2005: DOI:10.1126/science.1121536]

Tectonics - The structural arrangement of rocks in any crust of a planet. Used to understand rock structures. [Energy; v18; 1263-71; 1994.] [Science; v263; 1593-60; 1994: DOI:10.1126/science.263.5153.1593] [Science; v315; 1650-1651; 2007:DOI:10.1126/science.315.5819.1650b]

Temperature Inversion - The abnormal reversal of temperature in the troposphere caused by meteorological conditions. This leads to the entrapment of urban air pollution because mixing of surface air into the rest of the troposphere is limited. Under normal circumstances, air in the troposphere is cold at high altitudes and warm at low altitudes, or near the earth's surface. (See lapse rate.) When air pollutants, such as O3, SO2 or NOx, in urban areas get too concentrated, smog is produced. This can lead to human health disturbances in people with respiratory illnesses such as asthma. Surface temperature inversions are created when the lapse rate goes negative, that is, when the temperature profile of low lying tropospheric air increases with altitude. Air at the earth's surface is trapped there because the air above it is less warmer and less dense. This can be disastrous for the air quality in urban areas when anthropogenic pollutants are not mixed away from the surface and, instead, build up. In London, England in 1952, 4,000 people died during a four-day temperature inversion event in December. In Donora, Pennsylvania in 1948 a five-day temperature inversion trapped smog---made of soot, SO2, and metal fumes from a zinc works---that killed 20 people. [Alden, Robert. "1948 Donora Smog Killed 20; London Toll Was 4,000 in '52." New York Times 26 Nov. 1966: 28.] [Atmospheric Environment; v35; 2417-2421; 200; DOI:10.1016/S1352-2310(00)00523-9.] [Atmospheric Environment; v41; 327-338; 2007; DOI:10.1016/j.atmosenv.2006.08.012]

Termolecular Reaction - A reaction containing three particles. In the atmosphere an example of a termolecular reaction is one in which a molecule acquires the excess energy released by a reaction so that the products created do not convert back to the original state of the reactants. The reaction of molecular oxygen with an oxygen atom (radical) to produce ozone is a good example of an important atmospheric termolecular reaction. In the atmosphere this third body is most often molecular nitrogen because statistically this is the most likely next collision since atmospheric N2 is 78% by volume in the earth's atmosphere. [Analytical Chemistry; v27; 2021-24; 1994.] [Analytical Chemistry; v64; 1273-80; 1994.] [Journal of the American Society for Mass Spectrometry; v17; 544-561; 2006.]

Terpene - A naturally occurring organic compound, of the general empirical formula, C10H16, biologically built from a naturally occurring "monomer" called isoprene, C5H8, which is found as a volatile oil in plants. A clearly important--and olfactorily obvious--example is alpha-terpinene found in lemon oil. [Analytical Chemistry; v65; 2528-33; 1993.] [Atmospheric Environment; v36; 4347-4355; 2002; DOI:10.1016/S1352-2310(02)00355-2] [Analytica Chimica Acta; v559; 97-104; 2006: DOI:10.1016/j.aca.2005.11.056]

tert Butyl Alcohol - (t-butanol) A highly flammable, volatile, colorless liquid which has a camphor-like odor. It is miscible in esters, and aromatic and aliphatic hydrocarbons, and soluble in water. Based on its vapor pressure, tert-butyl alcohol will exist mainly in the vapor phase in the atmosphere. It is most likely to react with the hydroxyl (OH) radical at this state. The reaction products are formaldehyde and acetone. One of MTBE's atmospheric decomposition products is t-butanol. [Chemosphere; v53; 469-477; 2003.] [Atmospheric Research; v92; 124-130; 2009: DOI:10.1016/j.atmosres.2008.09.009]

Tertiary Period - This extended from about 65 million years ago to about 2.5 million years ago. [Atmospheric Change: An Earth System Perspective; p.13; 1993.] [Journal of Geochemical Exploration; v90; 24-44; 2006.]

Tetrachloroethane - No longer intentionally produced by industrial plants in the United States as an end product. In the past it was often used as a solvent and was a component found in several pesticides. There are several health hazards associated with short term and long term exposure. Long term exposure leads to damage of the central nervous system and liver. It is a colorless liquid that has a sweet chloroform odor, has a molecular weight of 167.85 g/mol, melting point of -43.8 degrees C, and is a corrosive liquid. [Environmental Pollution; v101; 221-230; 1998.] [Atmospheric Research; v89; 289-297; 2008; DOI:10.1016/j.atmosres.2008.03.013]

Tetrachlorethylene - This is used as a industrial cleaner. One of the most abundant pollutants in water pollution. This chemical degrades and can produce vinyl chloride which is a carcinogenic to humans. [Journal of Environmental Engineering and Science; v4; 11-15; 2005.] [Journal Exposure Analysis Environmental Epidemiology; v1; 475-490; 1991.] [Atmospheric Environment; v43; 1926-1931; 2009; DOI:10.1016/j.atmosenv.2008.12.038]

Tetrachloromethylene - This compound, also called perchloroethylene, is used for dry cleaning purposes; often it is recycled by the cleaners for reuse. [Water Research; v36; 1902-1908; 2002.]

Tetradecane - A light, oily hydrocarbon with a melting point of 5.89 degrees C and a boiling point of 253.7C. As a gas-phase pollutant it is inactive as a human contact allergen. [Environmental Health Perspectives; v105; 986-992; 1997.] [Journal of Hazardous Materials; v40; 213-235; 1995.]

Tetraethyl Lead (TEL) - C8H20Pb, an organometallic compound used as a gasoline additive that prevents engine knocking. Leaded fuel allows for better efficiency and decreased knocking in internal combustion engines, but the lead released in car emissions, as lead oxides, is very toxic to humans. Lead would get deposited on the road and get mixed into urban dust. Teraethyl lead incorporation in gasoline was developed by Thomas Midgley, Jr., later the inventor of chlorofluorcarbons. The advent of the catalytic converter's use in the 1970's precluded the use (in the U.S.) of leaded gasoline because Pb poisoned the metals used in that device. TEL was therefore substantially phased out over the next 20 years. [Analytical Chemistry; v68; p3008-3014; 1996.] [Atmospheric Environment; v37; 3077-3089; 2003.] [Atmospheric Environment; v43; 13-22; 2009: DOI:10.1016/j.atmosenv.2008.09.061]

1,2,3,4-tetramethylbenzene (C10H14) - An alkyl benzene, found in aircraft areas, burn pits, chemical disposal areas and marine sediments as well as urban exhaust plumes and in typical fuels. Molecular weight 134.22. This compound is involve in the urban environmental miasma, the chemical soup that produces oxidized hydrocarbons, aldehydes, ketones, oxides, peroxides, and ozone. [Environmental Science Technology; v25; 1112–1125; 1991; DOI:10.1021/es00018a015]

1,2,3,5 Tetramethylbenzene - A colorless, odorless, liquid with a boiling point of 197.9 degrees C. This chemical’s role in atmospheric chemistry lies in the fact that it is one of the hydrocarbons that helps create photochemical smog. It does this by being converted to the peroxide which can subsequently photooxidize nitrogen monoxide in the atmosphere to NO2. Nitrogen dioxide is photolyzed by sunlight to atomic oxygen which reacts immediately to produce ozone. When in high enough concentration, it can cause skin, eye, and lung irritation. [Environmental Science Technology; v4; 916-924; 1970; DOI:10.1021/es60046a002]

Thermal Conductivity - A given material’s ability to conduct heat energy. The process of conduction means that heat energy will flow through the material without the material moving to carry it. The heat energy inside the material will naturally flow to the area with the lowest temperature. Air has different thermal conductivity values at different temperatures. The ability of atmospheric air to house different thermal conductivities make it one of the many factors that influence the weather. [Journal of Physical and Chemical Reference Data.; v14; 947, 1985; DOI:10.1063/1.55574] [European Journal of Soil Science.; v53; 599-606; 2002; DOI: 10.1046/j.1365-2389.2002.00474.x]

Thermal-IR Radiation - Long wavelength solar radiation from the sun bounces off the Earth's surface or atmospheric gases as it is reflected back into the troposphere. In addition, shorter wavelengths of light are absorbed by the earth's surface and re-radiated to space in the IR. Thermal IR, and all IR, is invisible to the eye but can be felt with the skin. [Remote Sensing of Environment; v107; 402-413; 2007; DOI:10.1016/j.rse.2006.09.011] [Atmospheric Environment; v45; 716-726 ; 2011; DOI:10.1016/j.atmosenv.2010.09.043]

1,2,4,5-Tetramethylbenzene - chemical used in polyamide resin, plasticizer, and as an aromatic additive in gasoline. At room temperature it is a white, crystalline powder, an aromatic, with a molecular weight of 134.21. [Solid State Nuclear Magnetic Resonance, v13; 137-148; 1998.] [Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy; v63; 766-773; 2006.]

Thermodynamics - The science of heat and temperature and of the laws governing the conversion of heat into mechanical, electrical, or chemical energy. [Crutzen, Paul J. and Graedel, T.E. Atmospheric Change: An Earth System Perspective. Freeman Press; 1993; p. 436.] [Building and Environment; v46; 1747-1764; 2011; DOI:10.1016/j.buildenv.2011.02.001]

Thermosphere - The outermost shell of the atmosphere, between the mesosphere and outer space; where temperatures increase steadily with altitude. This begins at about 100 km altitude at a temperature of about -75 degrees C. [Journal Atmospheric Solar Terrestrial Physics; v69; 649-660; 2007; DOI:10.1016/j.jastp.2006.11.002][Journal Atmospheric Solar Terrestrial Physics; v71; 1514-1528; 2009; DOI:10.1016/j.jastp.2009.01.010]

Toluene (C6H5CH3) - a highly volatile and water-soluble benzene derivative that is highly toxic to most forms of life. Its estimated lifespan in the atmosphere--with respect to a photochemical reaction with hydroxyl radical---is 60 hours and this hydrocarbon is eventually oxidized to carbon dioxide. Toluene is used in a variety of industries including the manufacture of TNT, pharmaceuticals, rubbers, and other benzene derivatives, and is also a fuel additive and a paint solvent. Toluene also reaches the atmosphere from natural sources such as coal tar, mineral oils, and forest fires. [International Journal of Photoenergy, v2007; 1-8; 2007; DOI:http://dx.doi.org/10.1155/2007/32859] [Atmospheric Environment; v45; 2324-2334; 2011; DOI:10.1016/j.atmosenv.2010.11.007]

TOMS (Total Ozone Mapping Spectrometer) - An instrument that measures the total ozone in a vertical column of atmosphere. Measurements are made by comparing the amount of back scattered ultraviolet radiation with the amount of incoming solar energy. These changes in this ratio, the earth's albedo, at specific wavelengths can be used to determine the amount of ozone present. Four satellites create global maps daily of the earth's ozone measurements. [Ozone: Science & Engineering: Journal International Ozone Association; v26; 181 - 188; 2004; DOI:10.1080/01919510490439528] [Atmospheric Environment; v34; 2681-2690; 2000; DOI:10.1016/S1352-2310(99)00522-1]

Total Column Ozone - The total amount of ozone that is found in a column of air above the earth from the surface to the top of the atmosphere. The majority of this amount is typically found in the stratosphere. [Journal of Geophysical Research; v95; 13883; 1990.] [Atmospheric Environment; v45; 1648-1654; 2011; DOI:10.1016/j.atmosenv.2011.01.008]

Toxaphene - C10H22Cl8, is a pesticide used against insects, most commonly found in the gas or solid phase. Between 1947 and 1980 it was mainly used in the southern U.S. states, to keep insects from damaging cotton crops. Due to the fact that it is harmful for humans it has been banned in the United States. It is considered a persistent, bioaccumulative and toxic pollutant. Humans get exposed to toxaphene by eating it in contaninated food; it can even be passed on in breast milk, or to unborn children during pregnancy through the mother's blood stream. It can be transported through the air eventually falling to the ground with rain or snow.

Trace Gases - These are gases in the atmosphere that do not occur in large quantities but are significant to life on Earth or are important constituents of the chemical cycles in the atmosphere. [Journal of American Hygienist Association; v54; 639-46; 1993.] [Atmospheric Environment B; v27B; 275-82; 1993.]

Trade Winds - Wind systems occupying most of the tropics, which blow from 30 degrees North and South toward the equator; winds are northeasterly in the Northern Hemisphere and southeasterly in the Southern Hemisphere. [An Introduction to the World's Oceans; 5th edition; p493; 1997.]

Trajectory - The curve or a path that an object makes while in space. Trajectory is usually a set of points on the path taken [Sacramento Sinica; v47; 599-606; 2004.]

Trichloroethylene (TCE) - C2HCl3, this is an industrial solvent used primarily for vapor degreasing and cold cleaning. It is an extraction solvent for greases, oils, fats, waxes, and tars, and is used by the textile processing industry to sour cotton, wool, and other fabrics. Exposure to moderate amounts of trichloroethylene may cause various health effects such as headaches, vertigo, visual disturbance, tremors, and dizziness. Death may occur from inhalation of large amounts. People located near or downwind of sites where TCE may be in operation might be exposed to higher levels. It is a human carcinogen. [Journal of Environmental Management; v83; 56-65; 2007.] [Journal of Molecular Catalysis A: Chemical; v217; 109-115; 2004.] [Analyst; v136; 1664-1674; 2011; DOI:10.1039/C0AN00780C] [Chem Eng. News; v89(49); 26; 2011.]

1,1,2-Trichlorofluoroethane - C2Cl3F3 (CFC-113), a chlorofluorocarbon with a long atmospheric lifetime (~85 years) and the third highest abundance in the Earth's atmosphere (behind CFC-11 and CFC-12). It has been used as a working fluid and blowing agent. Like other stable CFCs, it can and will, however, rise above the troposphere and be photolyzed in the available UV radiation of the upper stratosphere, releasing atomic chlorine (Cl dot) which will ultimately catalytically destroy stratospheric ozone. The Montreal Protocol called for the phase out of CFC-113 by 2010. [Journal of Quantitative Spectroscopy and Radiative Transfer; v112; 1280-1285; 2011; DOI:10.1016/j.jqsrt.2011.01.023] [Atmospheric Environment; v42; 7706-7717; 2008; DOI:10.1016/j.atmosenv.2008.05.042]

Trichlorofluoromethane (Freon®-11, CFC-12) - One of the principal greenhouse gases, a gas with absorption bands in the infrared portion of the spectrum. There is extensive evidence showing that a class of synthetic compounds, the chlorofluorocarbons (CFCs), are responsible for the destruction of the ozone layer. CFCs are molecules that contain one or more atoms of both chlorine and fluorine. In September of 2004, the ozone hole over Antarctica was the largest area ever recorded and was almost THREE times larger than the area of the U.S. Because CFCs are so unreactive, they do not break down when released into the air in the troposphere where they are spilled. In time, air currents and diffusion carry them into the stratosphere, where, under the influence of UV radiation, they release chlorine radicals that initiate the destruction of ozone. Data collected by NASA have shown conclusively, that there is an inverse relationship between ozone concentration and the chlorine monoxide radical in the stratosphere; ClO is formed by chlorine atom attack on O3. CFCs are very useful inert, nontoxic, nonflammable compounds that had been used for years as coolants and as spray can propellants for aerosol forms of hair sprays and deodorants. They had been unsurpassed as solvents for cleaning electronic microcircuits. Commercially, the most important CFCs are the halogenated methanes, Freon-11 (trichlorofluoromethane) and Freon-12 (dichlorodifluoromethane). Over 50% of asthma inhalers contain chlorofluorocarbons as the solvent and gaseous propellent. These CFCs have relatively recently been prohibited in all products except in those medicinal inhaler dispensers for asthmatics and a few other limited exceptions. In Finland alone there are over a million medicinal dispensers that disperse freons into the atmosphere. This is equal to the freon concentration of the cooling devices in approximately l00,000 refrigerators. [Buell and Girard, Chemistry, Prentice-Hall, Inc., l994.] [Chemosphere; v24; 935-940; 1992.] [Chemical Physics Letters; v427; 241-245; 2006.]

Trifluralin - C13H16F3N3O4, usually found in the form of a yellow-orange crystal or solid. It is primarily used to manage broadleaf weeds on fruits, vegetables, flowers and shrubs. It enters the human body be either being eaten while consuming foods, by breathing it in the air or via contact with the skin. It is moderately toxic for small animal; in dogs, it can lead to weight loss, change in blood or increase in liver weight.

1,2,4-Trimethylbenzene - A colorless, flammable liquid with the formula C9H12. It occurs naturally in coal tar and petrleum crude oil and therefore ends up in gasoline. It is a major component (typically 40%) of a petroleum refinery distillation fraction known as the C9 aromatic fraction. Oil refineries produce large amounts of this substance each year. Most of the C9 fraction is usually added directly to gasoline. Exposure to 1,2,4 trimethylbenzene can occur in the workplace or in the environment following releases to air, water, land, or groundwater. Vehicle emissions are a major anthropogenic source of 1,2,4-trimethylbenzene, due to its widespread occurrence in gasoline. Once in air, it breaks down and contributes to photochemical smog when it reacts with other volatile substance. This compound is also used by industries as chemical raw materials, paint thinners, and solvents. [Atmospheric environment; v37; P2485-2496; 2003; DOI:10.1016/S1352-2310(03)00177-8]

1,3,5-Trimethylbenzene - C9H12, an aromatic hydrocarbon commonly used as an industrial solvent and also commonly found in urban air as a molecule originating from urban traffic. [Atmospheric Environment; v35; 753-760; 2001; DOI:10.1016/S1352-2310(00)00420-9] [Atmospheric Environment; v36; 6015-6030; 2002; DOI:10.1016/S1352-2310(02)00770-7]

Tropopause - The area where the temperature in the troposphere no longer decreases, indicating the boundary between the troposphere and the stratosphere. [Atmospheric Environment; v28; no1; 53-68; 1994.] [Journal of Atmospheric Science; v51; 509-29; 1994.]

Troposphere - The lowest layer of the Earth's atmosphere, ranging from the ground to the base of the stratosphere with a altitude of 10-15 kilometers depending on the latitude. This is where all weather occurs. The word troposphere is derived from the Greek words tropos--turning and spharia--sphere. [Science of The Total Environment; v374; 135-142; 2007.] [Journal of Atmospheric and Solar-Terrestrial Physics; v68; 523-538; 2006.]

Tundra - A high-latitude biome composed of limited biodiversity. Because of the colder temperatures compared to lower latitudes, plants are limited to small bushes, grasses, mosses, and lichens and almost no trees. Mostly below freezing, the temperature in the summer in the tundra can go above zero and cause partial thawing of the upper layers above the permafrost (frozen soil and dead plant stuff) for only a few days or weeks per year. Lots of carbon is stored in the thick mats in tundra layers for hundreds and thousands of years and, if long term temperature of the earth's tundra increases then biological degradation can cause the release of carbon in the form of methane or carbon dioxide. A fire in 2007 in Alaska released large amounts of this type of stored carbon. It's realistic to assume that tundral fires might increase if the earth's temperature warms--warming that recent widely measured temperatures and atmospheric modeling show occurs more at higher latitudes rather than lower--and so tundral fires can increase overtime. This would be a positive feedback cycle since this released carbon would contribute to global warming. [Eurasian Soil Science; v39; 314-323; 2006; DOI:10.1134/S1064229306030112][Nature 475-492; 2011; DOI:10.1038/nature10283]

Twilight - A period of time in either the early or later hours of the day, just before sunrise and after sunset, when the sun is below the horizon but the sky is still illuminated. Beams of light are scattered off of particles in the Earth's atmosphere, causing light to be seen even though the sun is not in the sky. This phenomena happens for a longer period of time in the more northern latitudes; in the far north or far south latitudes, twilight can last all night (at the opposite ends of the year). [Icarus; v59; 131; 1984; DOI:10.1016/0019-1035(84)90061-7] [Atmospheric Environment; v38; 6679-6685; 2004; DOI:10.1016/j.atmosenv.2004.09.007]

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UARS (Upper Atmosphere Research Satellite) - A satellite deployed (1991-2005) by NASA--using the shuttle Discovery--to study the chemistry in the upper atmosphere of Earth. Instruments on-board measured stratospheric ozone, methane, NOx, water vapor and temperature profiles among others. [Chemical and Engineering News; v70; 27-8; 1990.] [Manufacturing Systems; v8; 36-8; 1990.] [Journal of Geophysical Research; v104(D15); 18715-18737; 1999; DOI:10.1029/1999JD900225]

Ultraviolet Light - See UV-A, UV-B, and UV-C.

Umbra - During a solar eclipse the moon blocks the sun from shining on the Earth. In the umbra, the source of light is completely blocked by the moon causing the shadow on the Earth. An observer in the umbra experiences complete darkness. [Vistas in Astronomy; v14; 1-11; 1972.] [Physics of The Earth and Planetary Interiors; v4; 197-198; 1971.] [New Astronomy; v17; 112-116; 2012; DOI:10.1016/j.newast.2011.06.006]

Unleaded Gasoline - This fuel consists mostly of hydrocarbons and is sometimes enhanced with benzene to increase octane ratings and is used as fuel in internal combustion engines. Unleaded gasoline is manufactured to meet the requirement of new model automobiles in the US since 1975, because in that year catalytic converters were made mandatory for all vehicles sold in the US. Lead was removed from gasoline because lead emissions poison the metals used in catalytic converters. Lead had been added to gasoline since the 1920's as tetraethyllead (TEL), historically referred to as "ethyl." Exposure to high levels of lead can cause vomiting, diarrhea, convulsions, coma or even death, but lead emissions from automobiles consisted of lead oxide particles which settle out near highways. Lead removal from gasoline in the US has resulted in a clear, measurable decrease in lead in the urban environments in the US. [Fuel and Energy Abstracts; v47; 5; 2006.] [Applied Thermal Engineering; v27; 358-368; 2007.]

Uranium - A radioactive element found in the actinide series on the periodic table. It has the chemical symbol of U, standard atomic weight of 238.02891 and 92 protons. This element is useful producing energy needed to power cities and regions of countries. The fissionable isotope of uranium is uranium-235. Scientist discovered that this isotope could be induced to release energy when a thermal (slow) neutron strikes this isotope's nucleus producing smaller mass fragments, additional neutrons, and energy that stemmed from mass from those reactants converted to energy, the so-called mass defect. Nuclear plants were built to house this process beginning in the early 1950s. This process of splitting atoms is called fission. [Journal of Analytical Atomic Spectrometry; v17; 131-134; 2002; DOI:10.1039/B108414C]

Uranium-Thorium Dating - An absolute dating technique which uses the properties of the radioactive half-life of Uranium-238 and Thorium-230. The half-life of uranium-238 is 4.5 billion years, that is, in that many years half of the original amount is still uranium-238 while the other half has lost nucleons to form a different element which is more stable. [Quaternary Geochronology; v1; 289-295; 2006.]

Urban Air Pollution - Pollution that occurs in cities from the burning of fossil fuels and the emissions of hydrocarbons. Urban air pollution can be in the form of ozone, smog, acid rain, carbon monoxide, particulate matter (PM-10), and nitrogen oxides. [Journal of Environmental Management; v84; 27-37; 2007.] [Toxicology Letters; v168; 200-209; 2007.]

Urban Heat Island Effect - Urban heat island effect is the condition in which a city is relatively warmer than the surrounding areas due to the heat generated by the good conductors such as concrete, cars, and city buildings and the lack of vegetation. [Journal of Applied Meteorology, v7; 575-582; 1968.] [Renewable Energy; v32; 1805-1816; 2007.] [Remote Sensing of Environment; v106; 375-386; 2007.]

UV-A - Ultraviolet light that has wavelengths of 320 nm to 400 nm. The wavelengths of this light are shorter than visible light and are not absorbed in the stratosphere by ozone. [ Deep Sea Research Part I: Oceanographic Research Papers; v48; 741-759; 2001]

UV-B - An ultraviolet wavelength of light between 280 nm and 320 nm whose intensity is increasing at the earth's surface (probably causing increases in skin cancer), This UV increase is because of decreases in stratospheric ozone. [Research and Development Magazine; v39; 18LS; 1997.] [Chemical and Engineering News; v71; 12-13; 1993.]

UV-C - Light that spans the spectrum with wavelengths of 10 nm to 290 nm. These wavelengths of ultraviolet light are extremely dangerous to human and animal tissue and is totally absorbed in the stratosphere by ozone and molecular oxygen. [Environmental and Experimental Botany, v. 45, 1-9; 2001]

UV/Vis Spectrophotometry - Ultraviolet/visible spectrophotometry is used to measure the absorption capabilities of certain compounds with reference to wavelengths of light on the ultraviolet and visible light ranges. [Skoog, West, and Holler; Fundamentals of Analytical Chemistry. 7th ed. pg. 57-58; 1996.] [Journal of Photochemistry and Photobiology A: Chemistry; v187; 1-9; 2007.] [Atmospheric Environment; v29; 3239-3243; 1995.]

UV Radiation- energy that is emitted in the form of electromagnetic waves with a wavelength of 1-380nm, which is composed of UV-A, UV-B, and UV-C light; UV-A light being the longest wavelength and having the smallest energy and UV-C light being the shortest wavelength and having the highest energy. All UV-C light and most UV-B light is filtered out of the atmosphere via the ozone layer. However, UV-A light travels to the surface of the earth. [Environmental Pollution; v88n2; 219; 1995.] [Journal of Photochemistry and Photobiology B: Biology; v46; 5-19; 1998.] [Journal of Atmospheric and Solar-Terrestrial Physics; v67; 1321-1330; 2005.]

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Vadose Zone- The unsaturated zone in a soil where chemical processes are at their most active. Its extent is determined partly by the content of the soil water, but it cannot extend beyond the water table, below which voids are completely filled with water. [The Oxford Dictionary of Natural History. Allavy, M. Ed.; pg.662. Oxford University Press 1985.] [Advances in Water Resources; v30; 794-807; 2007.]

Valence Electrons - The outermost electrons of an atom that are in the orbitals of highest principal quantum number of all electrons in the atom and don't fill that orbital completely. [Physics Chemistry; v100; 5715-20; 1986.] [Organic Chemistry; 2nd ed; 48-50; 1997.]

Vapor A substance in the gas state that is below its critical temperature but still suspended in air. It is possible for a vapor to be liquefied by increased pressure. Vapors are usually not visible. [Environmental Pollution; v123; 413-425; 2003.] [Atmospheric Environment; v37; 1223-1230; 2003.]

Venus - Second planet from the sun; mass 4.872 x 1027g; radius of cloud surface about 6100 Km; radius of solid surface about 6056 Km; surface temperature 737K; temperature of cloud tops 250K; cloud composition more than 75% H2SO4 and about 25% water; atmosphere (by volume) 90-95% CO2 with traces of SO2, water, CO, H2SO4, Ar, Ne, HF, HCl. Atmospheric pressure 92-95 atm. [Hopkins, Jeanne. Glossary of Astronomy and Astrophysics. pg 187; 1980; University of Chicago Press.]

Vernal Equinox - A time during the spring season when the sun is directly above the equator which results in an equal amount of time for day and night. [Journal of Applied Meteorology; v30n4; 494; 1991.] [Journal of Atmospheric and Terrestrial Physics; v51n2; 111; 1989.]

Vertical Flux - In dry deposition this refers to the rate at which a gas particle is deposited onto another surface without the aid of precipitation. Vertical flux equals concentration of the species multiplied by the deposition velocity. [International Journal of Heat and Mass Transfer; v31n11; 2291; 1988.] [Journal of Atmospheric Sciences; v48n11; 1909; 1991.]

Vertical Mixing - The movement of air in a vertical direction usually caused by differences in temperature and density. [Atmospheric Environment; v26n6; 965; 1992.] [Journal of Geophysical Research; v99; 20345; 1994.]

Vinyl Bromide - a toxic compound that was established as a federal hazardous air pollutant in 1993. Sources of vinyl bromide may include rubber substitution, flame-retarding treatment of acrylics, laminating, and/or preparing films. It is also important to point out that vinyl bromide may be the result of the atmospheric degradation of 1,2-dibromoethane. Based on a typical atmospheric gas phase reaction with a hydroxyl radical, the lifetime of vinyl bromide in the atmosphere is between 1.5 and 2.1 days resulting in the products formaldehyde and formyl bromide. [Experimental and Molecular Pathology, v28; 25-33; 1978.] [Environmental Science Technology; 41; 1352-1358; 2007.] [Journal of Physical Chemistry A.; 105; 1830-1837; 2001.]

Vinyl Chloride - C2H3Cl, synonyms: Ethylene, chloro-; Chloroethene; Chloroethylene; Monochloroethylene; Vinyl chloride; Vinyl chloride monomer. This colorless gas is used mainly to produce polyvinylchloride. As there are no natural sources known for this compound, all sources are anthropogenic. The compound reacts with hydroxyl radicals in the troposphere to yield chlorine radicals. [Water Research; v35; 561-566; 2001.] [Atmospheric Environment; v30; 751-756; 1996; DOI:10.1016/1352-2310(94)00213-4] [Spectrochimica Acta Part A; Molecular Spectroscopy; V34; 481-487; 1978; DOI:10.1016/0584-8539(78)80043-9]

Visibility - A measurement of the ability to see and identify objects at different distances. Degradation of visibility is a negative effect of particulates in the environment. [Measurement Science and Technology; v5; 1505; 1994.] [Atmospheric Environment; v28; 3277; 1994; DOI:10.1016/1352-2310(94)00160-M] [Atmospheric Environment; v40 supplement 2; 593-605; 2006; DOI:10.1016/j.atmosenv.2005.11.076]

Visible Light - The light of the electromagnetic spectrum that we perceive with our naked eye. The wavelengths of light that we can see are between roughly 380 nanometers to 700 nanometers. Blue (shortest visible wavelength) light is preferably scattered by gases and particles in our atmosphere (see Rayleigh scattering) and this creates the blue sky that we perceive when looking away from the sun during daylight. When the sun is at its peak at noon, we see white light, since the light travels through the least amount of atmosphere, undergoing the least atmospheric scattering and therefore includes most of the visible wavelengths and therefore this mixture of light appears white. As the sun moves across the sky and the solar incident angle increases, the sunlight has to travel through more and more of the atmosphere--before it strikes our eyes at the surface of the earth--which causes increased scattering, again of blue light more than longer wavelengths. Mid-day, the sun will appear to be yellow and at sunset sunlight has to travel through the longest path of atmosphere scattering almost all blue, most green, and lots of yellow light, leaving mostly red sunlight to be seen by us. This means sunsets and sunrises often look reddish. [Optics Letters.; v1; 70-72; 1977; DOI:10.1364/OL.1.000070] [Atmospheric Environment; v43; 6136-6144; 2009; DOI:10.1016/j.atmosenv.2009.09.010]

Volatile Organic Compounds (VOC) - These are organic chemicals that have a very high vapor pressure and low solubility in water under normal atmospheric conditions. They tend to be much more concentrated as an indoor pollutant because of the numerous household items that contain them. Exposure to these VOCs can lead to eye, nose, throat irritation, headaches, nausea, and even liver damage. In polluted urban environments these compounds can contribute to the production of ozone. [Atmospheric Environment; v43; 13-22; 2009; DOI:10.1016/j.atmosenv.2008.09.061]

Volcanoes - Openings in the earth's crust that release molten rock, steam, reduced and oxidized compounds, and ash from within the earth's interior into the atmosphere. [Earth in Space; v4; 5; 1991.] [Icarus; v81; 298; 1989.]

W-Z

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Walker Cell - A zonal circulation of the atmosphere confined to equatorial regions and driven principally by the oceanic temperature gradient. In the Pacific, air flows westward from the colder, eastern area to the warm, western ocean, where it acquires warmth and moisture and subsequently rises. A return flow aloft and subsidence over the eastern ocean complete the cell. [Science; v295; 838-841; 2002; DOI:10.1126/science.1065835] [Journal of Atmospheric and Solar-Terrestrial Physics; v70; 1046-1055; 2008; DOI:10.1016/j.jastp.2008.01.009]

Water - Water consists of two hydrogen atom and one oxygen atom (H2O). Water covers three-fourths of the Earth's surface, 60-70% of the world's weight, regenerates and redistributes through evaporation and other atmospheric processes. Water is involved in electrical charge separation because it has two types and positions of atoms giving it a net dipole movement. Water vapor also absorbs 17% of solar radiation in the troposphere, thus making it one of the two principal greenhouse gases. Of the solar energy absorbed by the Earth's surface a little more than half goes into latent heat, which is heat absorbed by water because of its transformation from a liquid to a gas. When these molecules condense back into a liquid, usually higher in the atmosphere, they released that energy back into the atmosphere as local warming.[Chemical Reviews; v77; 219-262; 1977.]

Water Cycle- The process by which water is transpired and evaporated from the land and water, condensed in the clouds, and precipitated out onto the earth once again to replenish the water in the bodies of water on the earth.[International Journal of Climatology; v5; 589-606; 2007.]

Water Vapor - Water present in the atmosphere in gaseous form; the source of all forms of condensation and precipitation. Water vapor, clouds, and carbon dioxide are the main atmospheric components in the exchange of terrestrial radiation in the troposphere, serving as a regulator of planetary temperatures via the greenhouse effect. Approximately 50 percent of the atmosphere's moisture lies within about 1.84 km of the earth's surface, and only a minute fraction of the total occurs above the tropopause. [Radio Science; v33; 919-928; 1998.]

Weak Sun Paradox - This refers to the fact that our sun has probably increased its luminosity during its lifetime (approximately 3.5 billion years). This assumption is based on astrophysical observations of many other stars. The best scientific conclusions are that when our sun was young it had a luminosity (total energy output) of 70-80% of what it is today; however, there has clearly been (based on geological records and long term evidence for the presence of liquid water) approximately the SAME long term planetary temperature on earth (about 15 degrees C, averaged planet-wide) instead of colder earlier surface temperatures followed later by warmer surface temperatures. This paradox suggests that the planet's surface temperature may have been controlled by atmospheric gases whose concentrations varied over time while keeping (via the greenhouse effect) the surface temperature relatively constant (see Gaia hypothesis). [Science; v33n6; 20; 1993.] [The Atmospheric Journal; v98n6; 2268; 1989.] [Science, v177, 52-56; 1972.]

Wien's Displacement Law - The relationship between wavelength and temperature in relation to blackbody radiation. The wavelength decreases as the temperature increases. The common formula to determine this relationship is Plank's Formula. [Eisberg, R & Resnick, R. "Thermal Radiation." in Quantum Physics of Atoms, Molecules, Solids, Nuclei, & Particles. 2nd ed. New York: Wiley, 1985.]

Wind - The natural movement of air from one location to another in the planet's atmosphere due to differences in air pressure. For major urban centers, gaseous pollution produced there from, for instance, internal combustion engines can be moved from where those toxic substances are released downwind to the open ocean or otherwise away from the populated area. This transportation process takes times and the anthropogenic components react with each other and sunlight over time. This results in changing pollutant concentrations over time. Since wind is a physical movement of air, this also affects the mixing and dilution of atmospheric particles. Wind affects the process by which particles in the nucleation mode collide and coagulate to form accumulation mode then coarse mode particles, and in general, higher surface winds dilute and decrease particle formation from vapor phase condensation. [Nature Geoscience.; v2; 827-828; 2009; DOI:10.1038/ngeo705] [Atmospheric Environment; v37; 2629–2641; 2003; DOI:10.1016/S1352-2310(03)00206-1] [Atmospheric Environment; v41; 1759-1767; 2007; DOI:10.1016/j.atmosenv.2006.10.026]

Wind Energy - Using the wind to turn a windmill blade to generate electricity. The blades collect the wind's energy as it goes over the blades because they slow down the speed of the wind; the blades are spun and the wind is slowed. The blades are connected to a drive shaft which is turning an electric generator to produce electricity. [Energy Economics; v1; 1; 2007.]  [Renewable Energy; v32; 2242-2246; 2007.]

Wind Rose - A diagram that presents information about wind speed and direction for a particular area over a certain amount of time. The diagram is a circle with spokes. The center is 0 and as the wind frequency increases bars extend from the center of the circle to the outside of the circle, in the direction the wind is blowing. Direction can be determined by which way the bar is extending to the outside of the circle because the wind rose is set up like a compass. Information for a windrose is gathered by monitoring stations throughout the area being monitored. By determining wind speed, direction, and frequency with a wind rose, movement of air, and pollutants can be predicted. [Atmospheric Environment; v40; 7480-7493; 2006.] [Cold Regions Science and Technology; v47;171-179; 2007.]

Wet Deposition - The deposition of dissolved substances such as airborne particles and gaseous molecules by precipitation. Airborne particles/gaseous molecules in the atmosphere are trapped in water droplets due to falling precipitation (i.e. rain and snow). These substances are then dissolve in the water droplets and are deposited on the surface in which the water droplets come into contact with. [Environmental Science Technology; v34; 4294; 2000] [Environmental Science Technology; v34; 361; 2000] [Atmospheric Environment; v40; 5893-5901; 2006.]

Xylene - An aromatic hydrocarbon used as a common industrial solvent, also named dimethylbenzene; exists as 3 isomers: m-xylene, o-xylene, and p-xylene. Xylene is usually obtained from petroleum and natural gas distillates. It is used in paint, rubber and leather industries, and also as a cleaning agent or degreaser. [Atmospheric Environment, v. 33, Issue 7, 1085-1092; 1999.] [Toxicology; v231; 147-158; 2007.]

Younger Dryas Period - A transition from the last glacial period, to the present interglacial period punctured by a brief and intense return to cold conditions around 10,900 years ago. Scientists believe this occurred because of the changes in atmospheric circulation resulting from large releases of melt water from glaciers. [Quaternary Science Reviews; v25; 3-4; 2006.] [Science; v315; 439; 2007.] [Palaeogeography, Palaeoclimatology, Palaeoecology; v246; 307-330; 2007.]

Zeolite - Microporus silicate or aluminosilicate structured minerals that can act as an absorbing filter or sieve on a molecular level. Mainly used by the petroleum industry for the cracking of petroleum or use as a filter against various compounds. [Journal of Physical Chemistry; v100; 1814-19; 1996.] [Water Environment and Technology; v8; 14; 1996.] [Catalysis Communications; v8; 539-542; 2007.]

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