2014 Version

Atmospheric Chemistry Glossary


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Back Scattering - Process by which up to 25% of radiant energy from the sun is reflected or scattered away from the surface by clouds. Serves the greatest importance in the atmospheric heat budget. Large errors in the assumed value of this variable may have important effects on computer models of the atmosphere. [Radiation and the Cloud Process in the Atmosphere; Liou, K.N.; 194; 1992; Oxford Press; Oxford.] [ Man's Impact on the Climate; Mitchell, Murry; Ed. Williams A. Matthews; 173; 1971; Colonial Press; Baltimore.] [Atmospheric Environment; v36; 5479-5489; 2002: DOI:http://dx.doi.org/10.1016/S1352-2310(02)00664-7] [Physics and Chemistry of the Earth, Part B: Hydrology, Oceans and Atmosphere; v26; 239-245; 2001; DOI:10.1016/S1464-1909(00)00246-X]

Barometric Pressure - The downward pressure, at any given point in the atmosphere, of the gases directly above that point. Average pressure globally at sea level is 1,013,000 dynes per centimeter squared or 760 torr. This is defined as one atmosphere. [A Field Guide to the Atmosphere; Day, John and Schaefer, Vincent; 347; 1981; Houghton Mifflin; Boston.] [Ice Time; Levenson, Thomas; 69-70; 1989; Harper and Row; NY.] [Physics and Chemistry of the Earth; v27; 1387-1399; 2002: DOI:10.1016/S1474-7065(02)00076-1]

Beer's Law (Beer-Lambert law) - For monochromatic radiation, absorbance (A) is determined by the relationship: A = abc, with a = absorptivity, b = path length through the medium, and c = concentration of the absorbing species. The intensity of a ray of light which has gone through a medium is a function of the path length through which the light passes and the concentration of absorbing matter in that medium. [Fundamentals of Analytical Chemistry; Skoog, Douglas A.; West, Donald M.; Holler, James F.; Ed. Jennifer Bortel; p. 510; 1996; Saunders College Publishing; Fort Worth, Texas.] [The Gulf Publishing Company Dictionary of Business and Science; Tver, David F.; p. 58; 1974; Gulf Publishing Company; Houston, Texas.] [Physics and Chemistry of the Earth; v27; 355-362: 2002: DOI:10.1016/S1474-7065(02)00012-8]

Benzene - C6H6, an aromatic hydrocarbon. It can be found in the air by several different ways of transmission. It can be produced for use with plastic or produced through the burning of fossil fuels. Benzene can also be found in the soil as well as some areas of groundwater pollution. In urban setting its presence correlates with the presence of NOx and CO. Exposure to benzene has been linked to leukemia. [Journal of Applied Meteorology; v38; 1448–1462; 1999; DOI:10.1175/1520-0450(1999)038<1448:AAOSOG>2.0.CO;2] [Atmospheric Environment; v41; 554-566; 2007; DOI:10.1016/j.atmosenv.2006.08.051]

Biogenic Emissions - The chemical compounds that living organisms put into the atmosphere, usually related to respiration or fermentation. Monitoring the biogenic emissions helps determine the source and sink of chemicals as well as atmospheric cycles. Examples of atmospheric components from biogenesis are methane, nitrous oxide, or terpenes. [Ecological Applications; v7; 46-58; 1997.][Agricultural and Forest Meteorology; v149; 808-819; 2009; DOI: 10.1016/j.agrformet.2008.11.001 ]

Biogeochemical Carbon - The biological and geographic study of the properties of carbon's chemical properties in relation to gases in the atmosphere. Models that study this often incorporate atmospheric carbon dioxide, carbonates in the ocean, organic carbon, and dissolved inorganic carbon in an attempt to determine the temporal characteristics of the planet's carbon cycle. [The Ages of Gaia; Lovelock, J.; pg. 30, 34, 62; 1988; Bantam; NY.] [Climate Systems Modeling ; Salby, Murry; Ed. Kevin E Trenberth; pg. 452, 489; 1992; Cambridge University Press; London.] [Global and Planetary Change; v35; 131-141; 2003.] [Earth and Planetary Science Letters; v286, 316-323: 2009; DOI:10.1016/j.epsl.2009.06.045]

Biological Amplification or Bioaccumulation - Increase in concentration of DDT, PCB, and other slowly degradable, fat-soluble chemicals in organisms at successively higher levels. [Miller, Tyler G.; Living in the Environment: Principles, Connections, and Solutions, (1996) Wadsworth Publishing, New York.] [Bioresource Technology; v98; 2178-2183; 2007.] [Critical Reviews in Toxicology; v34; 301-333; 2004.] [FEMS Microbiology Reviews; v11; 297-316; 1993.]

Biomass - The complete dry weight of organic material found in the biosphere or less strictly, the matter in the biosphere that is contained in living organisms. [Biology; Campbell, Niel; 1118; 1990; Benjamin Cummings, Redwood City.] [ Living in the Environment; Miller, Tyler; 467-470; 1994; Wadworth; Belmont.]

Biomass Burning - the process of oxidizing living material. This process produces atmospheric particulates as well as the production of greenhouse and reactive tropospheric gases. These gases include CO2, CO, NOx, CH4, CH3Cl along with the addition of black carbon. All of these chemical species can be lofted relatively high in the atmosphere due to the convective heating of a fire. [Graedel, T.D. and Paul Crutzen. Atmospheric Change: an Earth system perspective; 1993; Freeman Press.] [Atmospheric Environment; v41; 2644-2659; 2007.] [Remote Sensing of Environment; v107; 81-89; 2007.]

Biosphere - A volume including the lower part of the troposphere (as high as living organisms can fly or be lofted) and the surface of the earth including the oceans. This region, by definition, encompasses all the living matter of the earth. Some very important atmospheric chemicals are produced in this region and pass into the atmosphere. This region exchanges chemicals and particulate matter with the atmosphere and soils and waters of the earth. [Journal of Geophysical Research; v99; 16511-16521; 1994.] [Journal of Hydrology; v337; 258-268; 2007.] [Journal for Nature Conservation; v15; 26-40; 2007.]

Black Carbon - Emitted during the burning of coal, diesel fuel, natural gas and biomass and is part of the composition of soot.  Black Carbon can absorb and reflect sunlight cooling the Earth’s surface, but also increase solar energy absorbed in the atmosphere, warming it.  These effects are thought to effect global climate and rainfall cycles.  Black carbon increases the effect of global warming, visibility problems, and health problems. [Science; v307; 1454; 2005: DOI:10.1126/science.1104359] [Environmental Science Technology; v39; 1861; 2005; DOI:10.1021/es0493650

Blackbody Radiation - Any physical body absorbs and emits electromagnetic radiation when its temperature is above absolute zero. Planck's law determines the radiant flux of a body at a specific wavelength. In atmospheric chemistry, the calculation involving the earth's blackbody radiation shows that the earth's surface temperature would be below the freezing point of water if it did not have an atmosphere which absorbed some of the outgoing radiation. [Physical Review A; v45; 8471-8487; 1992; DOI:10.1103/PhysRevA.45.8471] [Science; v232; 1517-1522; 1986: DOI:10.1126/science.232.4757.1517]

Blue Sky - See Visible Light.

Bolide Impacts - Asteroids or comets striking the earth; a possible cause of major climate changes and mass extinctions in the Earth's history. [Bioscience; v44; 173-176; 1994.] [Nature; v342; 139-142; 1989.] [Sedimentary Geology; v108; 45-90: 1997; DOI:10.1016/S0037-0738(96)00048-6]

Boundary Layer - An area in the troposphere which is affected by the solar heating, radioactive cooling, and surface friction of the earth. The height of the boundary layer can range anywhere from 100m to 3 km and coincides with the height at which pollutants are mixed. The area immediately above the boundary layer is called the free troposphere. [Journal of Applied Meteorology; v28, pages 885-903; 1989.] [Atmospheric Environment; v37; 2193-2205; 2003; DOI:10.1016/S1352-2310(03)00157-2] [Atmospheric Research; v75; 301-321; 2005; DOI:10.1016/j.atmosres.2005.01.005]

Bromochlorodifluoromethane - [CAS# 353-59-3] Chemical formula CBrClF2 Synonyms: Halon 1211, Freon 12B1, chlorodifluorobromomethane. This chemical belongs to the freon family. Halon 1211 was introduced in the 1960s as an effective gaseous fire suppression agent for application in the protection of computer control rooms, museums, telecommunication switches and other areas containing highly valuable materials. Results of studies done in the late 1980s indicated that the agent was an ozone depleting chemical. This chemical is stable in the troposphere but photodissociates to yield halogen radicals in the upper atmosphere, which can catalytically destroy stratospheric ozone. [American Journal of Emergency Medicine; v14; 675-677; 1996.] [Atmospheric Environment; v40; 7331-7345, 2006; DOI:10.1016/j.atmosenv.2006.06.041]

Bromomethane - CH3Br, a volatile compound with a high mixing rate in the atmosphere. Methyl bromide escapes easily into the atmosphere where it can contribute to the depletion of ozone in the upper atmosphere. It works similarly to CFCs in its reaction with ozone molecules (O3). In the stratosphere, with the sun's UV light as a catalyst, methyl bromide breaks down and exchanges a bromide ion for oxygen from ozone. By breaking down the ozone molecules in the stratosphere, methyl bromide thins the ozone layer and lets more UV light pass through. [Chemosphere; v31; 3387-3395; 1995; DOI:10.1016/0045-6535(95)00190-J] [Ecotoxicology and Environmental Safety; v33; 100-101; 1996; DOI:10.1006/eesa.1996.0011]

Bromotrifluoromethane - Also known as Halon-1301, this chemical with formula CBrF3 is one of the most ozone destructive substances known to man. It is listed as a Class I ozone depleting chemical in the United States Clean Air Act amendments of 1990. This chemical is commonly used in fire fighting equipment used around sensitive electronic equipment such as computer rooms, telecommunication centers, and aviation equipment. It is know to cause headache and unconsciousness in humans. [Fundamental and Applied Toxicology; v20; 231-239; 1993.] [Journal of Chromatography A; v903; 261-265; 2000.]

Brownian Motion - Three-dimensional, random movement of particles in a gas or liquid. [Journal of Chemical Education; v65, 1091-1093; 1988.] [Environmental Science and Technology; v25; 2031-2037; 1991.]

1,3-Butadiene - CH2=CH-CH=CH2, is produced during a petrochemical combustion. It is also leaked into the atmosphere from the storage of petrochemicals. Typical half-life in the atmosphere is around 2 hours. It is also a known human carcinogen. [Chemico-Biological Interactions; v166; 44-51; 2007.] [Atmospheric Environment; Volume 40; 7686-7695; 2006.]

Butanal - C4H8O - A highly flammable, corrosive compound that causes burns; the aldehyde of butane. Also a colorless liquid, with a pungent smell that condenses and oxidizes in higher temperature of the atmosphere and contributes to photochemical smog. [Journal Photochemistry Photobiology A: v143; 169-179; 2001; DOI:10.1016/S1010-6030(01)00524-X] [Atmospheric Environment; v38; 4371-4382; 2004: DOI:10.1016/j.atmosenv.2004.03.035]

2-Butanone - CH3C(=O)-CH2CH2 also known as methyl ethyl ketone, 2-butanone is a product of the manufacturing of paints, glues, and other finishes because of its dissolving ability. A byproduct in the exhaust of automobiles, 2-butanone can easily evaporate into the atmosphere. It has been detected in both indoor and outdoor air. While in outdoor air it is produced by the photoxidation of certain air pollutants, such as butane and other hydrocarbons. Is known to have negative health effects when breathed in at high concentrations. [Talanta; v72; 539-545; 2007.] [Science of the Total Environment; v368; 574-584; 2006.] [Atmospheric Environment; v34; 2063-2101; 2000; DOI:10.1016/S1352-2310(99)00460-4]

t-Butylbenzene - Chemical formula is C10H14 molecular weight 134.21 grams. This chemical is highly flammable and easily ignited by heat, sparks or flames. It is also less dense than water and insoluble in water and is a colorless liquid. This chemical is an aromatic hydrocarbon used in hydrocarbon fuels. In combustion processes it contributes to the formation of mutagenic and carcinogenic compounds such as benzo(a)pyrene. [Progress Energy Combustion Science; v37; 330-350; 2011; DOI:10.1016/j.pecs.2010.06.004] [Atmosfera; 23; 165-183; 2010.] [Experimental Medicine and Biology; 459; 179-193; 1999.]


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Cap and Trade - for carbon regulation, a method of decreasing carbon emissions by setting (annual) regulatory limits on large, industrial CO2 emitters and fining them if they surpass that limit. Emitters that can decrease their annual CO2 emissions are allowed to sell the rights to emit the balance to other emitters which can't as easily decrease emissions. These traded emission right prices are set by the market and, in theory, these trades allow those who need to purchase the emission rights a chance to save money over the fines. Gradually the regulatory emission limits, the caps, are lowered and this pushes total emissions down over time. A system like this has been in place for sulfur dioxide emissions in the US since the 1990s and for NOx since 2003. This can be contrasted with a carbon tax. [Energy Economics, in press; 2009: DOI:10.1016/j.eneco.2009.02.003][Journal of Environmental Economics and Management; v56; 131-140, 2008; DOI:10.1016/j.jeem.2007.12.004]

Carbon 14 - 14C, an isotope of carbon-12 (12C). 14C contains two more neutrons and is radioactive and used in carbon dating. While carbon-12 is not radioactive, the half life of 14C is 5730 years. This relatively short half life allows the ratio of carbon-12 to carbon-14 to be used to date objects containing carbon to an age of 50,000 years before present time. [Journal of Hydrology; v430; 50-68; 2012; DOI:10.1016/j.jhydrol.2012.01.046]

Carbonate-Based Carbon Dioxide Capture - Carbon dioxide in combustion-produced flue gases can be dissolved in carbonate-containing solutions to form bicarbonates, thereby concentrating CO2 for subsequent sequestration. Heating of the bicarbonate-containing solution releases CO2, reforming carborbonates which can be recycled. A molten carbonate fuel cell technology is also under development. [International Journal of Greenhouse Gas Control; v2; 9-20; 2008; DOI:10.1016/S1750-5836(07)00094-1] [International Journal of Greenhouse Gas Control; v9; 372-384; 2012; DOI:http://dx.doi.org.ezproxy.shsu.edu/10.1016/j.ijggc.2012.05.002]

Carbon Cycle - A complex cycle that circulates carbon through the atmosphere, oceans, and land which includes vegetation and soil and carbon is in various forms and oxidation states throughout the cycle. [American Scientist; v78; 310-326; 1990.] [Journal of Forestry; v88; 33-34; 1990.]

Carbon Dioxide - CO2, a volatile compound consisting of one carbon and two oxygens. It is a reactant in photosynthesis and necessary for plant life, and is abundant in the atmosphere due to anthropogenic and natural activities. It is a greenhouse gas. The atmospheric concentration of carbon dioxide has been rising from a preindustrial value (<AD1800) of about 280 ppmv to a May 2014 level of about 402 ppmv as measured at Mauna Loa Observatory, Hawaii. This is an increase of over 40%. C. David Keeling was instrumental in establishing the first, high precision, continuous measurements of atmospheric carbon dioxide. The continuous, upward sloping plot of atmospheric CO2 concentration versus times is eponymously known as the Keeling curve. Ice core data from the European Project for Ice Coring in Antarctica show that present atmospheric concentrations of CO2 and CH4 are the highest in the past 800,000 years as determined in the so-called Dome C ice core. [Journal of Geophysical Research; v96; 7301-7312; 1991; DOI:10.1029/90JD02713] [Environmental Science and Technology; v28; 1565-1576; 1994; DOI:10.1021/es00058a006] [Atmospheric CO2 and 13CO2 exchange with the terrestrial biosphere and oceans from 1978 to 2000: observations and carbon cycle implications; C. D. Keeling, S. C. Piper, R. B. Bacastow, M. Wahlen, T. P. Whorf, M. Heimann, and H. A. Meijer; pp. 83-113, in "A History of Atmospheric CO2 and its effects on Plants, Animals, and Ecosystems", editors, Ehleringer, J.R., T. E. Cerling, M. D. Dearing, Springer Verlag, New York, 2005; DOI: 10.1126/science.1141038]

Carbon Dioxide Capture - See Carbon Sequestration.

Carbon Disulfide - CS2, a compound used to manufacture products such as rayon and cellophane. Carbon disulfide is produced naturally by microbial activity in marshes and in volcanic ash. Since carbon disulfide does not adhere well to sediments, if it comes into contact with soil, it could percolate into groundwater, where it is very soluble. CS2 can also add to photochemical smog development when it reacts with other organic substances in the atmosphere, such as methane or oxides of nitrogen. [Analytical Chemistry; v1753 -1755; 1997.] [Environmental Science and Technology; v35; 2543-2547; 2001.]

Carbon Monoxide - CO, a toxic, odorless, colorless gas produced during fossil fuel or biomass burning. Compound consisting of one carbon and one oxygen. Except for carbon dioxide, it is one of the longest lived naturally occurring atmospheric carbon compounds (this wording is meant to exclude chlorofluorocarbons). The recent change in tropospheric CO content may portend a change in the balance between oxidants and reductants in the atmosphere. [Journal of Geophysical Research; v95; 16443-16450; 1990.] [Scientific American; v261; 82-88; 1989.]

Carbon Sequestration - A method of capturing carbon dioxide so that it is not released into the atmosphere; also called carbon storage. This is a proposed response to the increase of CO2 in the atmosphere---mostly from anthropogenic sources since the industrial revolution. It can be achieved chemically in two obvious ways: carbon dioxide can be captured after a fossil fuel has been combusted in either the concentrated exhaust stream or, for example, carbon dioxide can be generated in fuel consumption/precombustion in the so-called syngas (synthesis gas) process which produces molecular hydrogen and CO from a methane-rich feed gas. That mix reacts with high temperature steam to produce H2 and CO2 which is captured. H2 is burned to produce energy. Even more difficult is collecting CO2 from the atmosphere at ambient concentrations in tropospheric air. Carbon dioxide produced by hydrocarbon combustion can be pressurized and injected into old salt mines or used in enhanced oil recovery. [Journal American Chemistry Society; v131, 5777–5783; 2009; DOI:10.1021/ja8074105] [Energy Environmental Science; v4; 444-452; 2011; DOI:10.1039/C0EE00213E] [Advanced Functional Materials; v19, 3821–3832; 2009; DOI:10.1002/adfm.200901461] [Journal American Chemistry Society; v133; 5664–5667: 2011; DOI:10.1021/ja111411q] [International Journal of Greenhouse Gas Control; v2; 9-20; 2008; DOI:10.1016/S1750-5836(07)00094-1]

Carbon Storge - See Carbon Sequestration.

Carbon Tax - A monetary dividend, which is agreed to be paid in order to emit carbon dioxide from such sources as burning of fossil fuels and biofuels. It acts as a central mechanism for reducing carbon emissions in the Earth's atmosphere. This can be contrasted with cap and trade. [Ecological Economics; v66; 379-91; 2008; DOI:10.1016/j.ecolecon.2007.09.021][Science; v315; 1670; 2007; DOI:10.1126/science.1138299][Science; 304; 1429; 2004; DOI:10.1126/science.304.5676.1429]

Carbon Tetrachloride - CCl4, a compound consisting of a carbon and 4 chlorines that is active in ozone depletion when the compound is broken down and releases chlorine atoms (radicals). Chlorine reacts with the ozone creating diatomic oxygen and chlorine monoxide which cycles back to chlorine radicals. [Environmental Science and Technology; v28; 1243-1247; 1994.] [Journal of the Air and Waste Management Association; v41; 1579-1584; 1991.]

Carbon Tetrafluoride - CF4, is known as Freon 14, carbon tetrafluoride is a stable, non-flammable, colorless gas. It absorbs light at 8 mm (in the infrared), is very stable, and does not react with water. This compound is theoretically considered a likely candidate for warming the earth during the next ice age. [Chemical Physics Letters; 2; 663-664; 1968.] [International Journal or Mass Spectrometry and Ion Physics. 47; 159-162; 1983.]

Carboniferous Period - The time period between 280-345 Myr BP of Earth's geologic history. Characterized by glacial onsets and melting and massive migration and extinctions of species during this period. [Geology; v18; 809-811; 1990.] [Geology; v17; 408-411; 1989.]

Carbonyl Sulfide - COS, a gas that is very stable and unreactive in the troposphere, but, it is thought, photolyzes to form carbon monoxide, CO, and sulfur, S, in the stratosphere. Through stratospheric chemical reactions, the sulfur atoms are converted to SO2 and H2SO4 which form sulfate aerosol and cloud condensation nuclei, but eventually settle into the troposphere and react to form sulfuric acid, a component of acid rain. Volcanic eruptions contribute some of this COS to the atmosphere. The major biospheric sources of COS are thought to be biological. [Analytical Chemistry; v 65; pages 976-982; 1993.] [Atmospheric Chemical Compounds: Sources, Occurrence, and Bioassay; Graedel, Hawkins, Claxton; page 513; 1986; Academic Press; Orlando.] [Science; v300; 307-310; 2003.]

Catalytic Converter - An air pollution control device using the exhaust system of cars. The converter helps complete combustion of any fuel that was not burned in the engine and reduce the presence of other harmful emission concentrations. The converter changes the unburned hydrocarbons and carbon monoxide in the exhaust into carbon dioxide and water vapor. The converter use chemical catalysis to create this change. [Fleisher, Paul. Ecology A to Z. Dillon Press, New York. 1994. p. 38.] [Catalysis Today; v98; 345-355; 2004.] [Chemical Engineering Science; v59; 5597-5605; 2004.] [Energy Conversion and Management; v47; 2811-2828; 2006.] [Applied Catalysis B: Environmental; v70; 305-313; 2007.]

Catalytic Destruction of Ozone - In the stratosphere, anthropogenic chlorine, mostly from chlorofluorocarbons is released as atomic chlorine (a radical) and becomes involved in a chemical cycle that destroys stratospheric ozone:

CF2Cl2 + hv ---> Cl + CF2Cl (this reaction produces chlorine radicals and the other chlorine atom is ultimately also freed for O3 destruction)

catalytic cycle:
Cl + O3 ---> ClO + O2
(chlorine reacts with ozone to form chlorine monoxide)
O3 + hv ---> O + O2
(ozone is also photolyzed to produce atomic oxygen)
ClO + O ---> Cl + O2
(chlorine radicals are reformed)
NET: 2O3 -> 3O2
(the result is conversion of ozone to molecular oxygen without ozone and atomic oxygen collision)

Atmospheric data have recently shown that the systematic banning of anthropogenic chlorine-containing compounds, CFCs such as Freon-11 and Freon-12, beginning with the Montreal Protocol in 1986, have stopped the degradation of stratospheric ozone, and a healing of this important atmospheric component is underway. And although recent estimates put the return to pre-damage stratospheric levels (< 1979) as being achieved by about 2050, the use of cheap air conditioning systems (using banned CFCs or replacement HCFCs that have otherwise been phased out) in developing countries like India and China may push that "cured" date back by decades. [Bradsher, K.; New York Times, Feb. 23, 2007.] [Journal of Physical Chemistry; v100; 453-457; 1996; DOI:10.1021/jp952445t] [Environmental Science Technology; 20; 328-329; 1986; DOI:10.1021/es00146a601] [Journal of Geophysical Research v111; D17309; 2006; DOI:10.1029/2005JD006371]

CFCs - See chlorofluorocarbons.

Chappuis Band of Ozone Absorption - The wavelengths of light absorbed by ozone in the visible region, approximately 380 to 750 nm. Compare to ozone's ultraviolet absorption region, the Hartley-Huggins band. [Nature v261, 289; 1976.] [Journal Chemical Physics; v108; 498; 1998: DOI:10.1063/1.475413] [Advances in Space Research; v34; 769-774; 2004; DOI:10.1016/j.asr.2003.08.058]

Chemical Lifetime - The length of time a chemical species can survive without reacting, photolyzing, dissociating, or otherwise changing into another chemical species. Highly reactive chemicals have short lifetimes. For instance, if the reaction rate of a target species with an attacking species is very fast then the lifetime of the target species will be short. For example, the reaction of smalls radicals like hydroxyl radical in the troposphere is very fast with many common tropospheric species, and therefore the tropospheric lifetime of hydroxyl radical is measured in seconds. [Environmental Science and Technology; v27; 1448-1452; 1993; DOI:10.1021/es00044a022] [Nature; v 350; pages 406-409; 1991; DOI:10.1038/350406a0] [Atmospheric Environment; v34; 5271-5282; 2000; DOI:10.1016/S1352-2310(00)00345-9]

Chloracne - A painful, disfiguring condition similar to common acne that it caused by people being exposed to high concentrations of PCB's (polychlorinated biphenyls). It is a biological response to the exposure of different types of organochlorine compounds. [Pollution Engineering; v29n10; 7; 1997.] [Pollution Engineering; v28n9; 73; 1996 Sept.] [Chemosphere; v60; 898-906; 2005.] [Toxicology; v229; 101-113; 2007.]

Chlorine - Cl2, molecular chlorine. In the stratosphere, atomic (radical) chlorine is very destructive because it depletes the greatly needed ozone layer which protects the earth from ultraviolet radiation from the sun. In the Antarctic stratosphere, molecular chlorine along with nitric acid are formed by the reaction of hydrogen chloride and chlorine nitrate--both stratospheric chlorine reservoir species. This process occurs on polar stratospheric clouds which serve as the reaction sites. Once formed, Cl2 vaporizes into the surrounding air as nitric acid--also formed in that process--binds with the ice matrix. Cl2 is then photodissociated in sunlight (lambda <= 450 nm) into chlorine radicals. These chlorine radicals then catalytic destroy ozone. [Graedel, T. E. and Crutzen, Paul J. Atmospheric Change, An Earth System Perspective. pgs 145-6. W. H. Freeman and Company, 1993.] [Science; v292; 61-63; 2001.]

Chlorine Atoms - Cl, the seventeenth element in the periodic table of elements. It has a atomic weight of 35.453 grams per mole. It has 17 protons in its nucleus and 7 electrons in its outer shell, an odd number which makes this neutral atom a radical and a very effective catalyst in the reaction that breaks down ozone in the stratosphere over Antarctica (see chlorine monoxide). [Science; v 264; pages 32-33; 1994.] [Science; v 262; pages 1703-1706; 1993.]

Chlorine Dioxide - ClO2, a radical, undergoes photodecomposition in the stratosphere where the products of this reaction react with ozone. Since this is a photochemical reaction it only takes place while the sun is up. Experiments over Antarctica have shown a direct relation between polar ozone loss and the increase in halocarbon chemistry, which comes from anthropogenic sources. Scientist are currently looking at the molecular behavior of chlorine dioxide in the atmosphere in order to understand its role in depletion of ozone more thoroughly. [Simon, J. D. and Vaida, V. The Photoreactivity of Chlorine Dioxide. Science v 268; p. 1443-1448; 1995.]

Chlorine Monoxide - ClO, a radical species (with an odd number of electrons in its outer shell) which plays an important role in the breakdown of stratospheric ozone over Antarctica. Formed by the photolysis of CFCs in the stratosphere and the subsequent destruction of an ozone molecule, these radicals can act as a catalyst in the destruction of ozone while not being destroyed themselves. ClO, reacting with a oxygen atom (present from the Chapman Mechanism), releases a free chlorine radical once again. As a result, one Cl atom can destroy thousands of ozone molecules before being sequestered as HCl or another reservoir species (see chlorine nitrate). [Earth Island Journal; v 7; page 18; 1992.] [Chronicle of Higher Education; v 38; pages A6-A7; 1992.]

Chlorine Nitrate - ClONO2, this is a stratospheric reservoir species for chlorine and nitrogen, two of the catalysts in the stratospheric breakdown of ozone. Frankly, it is named in a confusing manner; it is formed from the reaction of chlorine monoxide and nitrogen dioxide (not chlorine atoms with nitrate). It reacts with HCl at low temperatures on the surfaces of polar stratospheric clouds (PSCs over Antarctica and probably also in the stratosphere over the Arctic). That normally slow reaction heterogeneously produces molecular chlorine and nitric acid. The former outgases from the PSC surface and is quickly photolyzed by 450 nm or shorter wavelength light to form chlorine radicals which rapidly catalyze the breakdown of ozone (see chlorine monoxide). [Science; v 238; pages 1258-1260; 1987.] [Science; v 258; pages 1342-1345; 1992.]

Chlorobenzene - C6H5Cl, a colorless liquid that is manufactured for use as a solvent. It quickly evaporates in the air and is degraded by hydroxyl radicals that are produced photochemically. The gas acts as a source of ClO, which helps in the breakdown of stratospheric ozone. [Science; v224; 308-321; 1954.][Analytica Chimica Acta; v584; 189-195; 2007.]

Chlorodifluoromethane (HCFC-22) : CHClF2, this chemical is an intermediate replacement for the old CFCs because it contains a hydrogen atom, making a molecule that is easily attacked by hydroxyl radical in the atmosphere, therefore causing it to have a shorter atmospheric lifetime compared to the CFCs it replaces. In the U.S. HCFC-22's use is already being phased out but the phase out in developing countries like India is stumbling and this may lead to a slower healing of the stratospheric ozone layer's ozone. [Reviews of Geophysics; v13; 1-35; 1975; DOI:10.1029/RG013i001p00001] [D. DesMarteau and A. Beyerlin. New Chemical Alternative for the Protection of Stratospheric Ozone.][EPA/600/SR-95/113, p1-4.] [Bradsher, K.; New York Times, Feb. 23, 2007.]

Chloroethane - this manmade VOC is highly reactive in the atmosphere. It is a gas at room temperature and when released, it readily reacts with oxidizing agents, most quickly with hydroxyl radical, half life ~ 40 days. The subsequent products are removed via sedimentation, precipitation, or rainout. Chloroethane has been used in the manufacturing and production of insecticides, dyes and drugs; as a solvent; and as a fugitive emission from landfills. [Chemistry and Materials Science, v333; 700-701; 1989.]

Chlorofluorocarbons-CFCs - Very stable chemical compound, used in refrigerants, solvent, and (in the past in the U.S. ) aerosols, which release chlorine (important) and fluorine (less important) into the upper atmosphere. In the stratosphere, CFCs are photolyzed (by incoming solar UV) to form carbon dioxide, CO2, hydrogen fluoride, HF, and ultimately (after multiple UV absorption events) chlorine radicals. These chlorine species are crucial in the destruction of the ozone layer over Antarctica and probably elsewhere (see chlorine). [Environmental Science and Technology; v 28; pages 1619-1622; 1994.]

Chloroform - CHCl3, a colorless liquid that evaporates easily into the air. The compound is released into the air by direct and indirect sources and breaks down in the lower atmosphere into carbon dioxide, phosgene (carbonic dichloride), and hydrogen chloride. The degradation occurs in the troposphere by the reaction of the compound with hydroxyl radicals. [Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy; v106; 231-235; 2013; DOI:10.1016/j.saa.2012.12.073]

Chloromethane - A colorless gas with a sweet odor. It was once used as a refrigerant in consumer products, but is no longer used because of its toxicity. It is central nervous system irritant, and in high doses can cause paralysis, seizures, and coma. Chloromethane was first synthesized by Peligot in 1835. Its chemical formula is CH3Cl, and it has a melting point of -97°C, a boiling point of -24°C, and is naturally produced by sunlight reacting with biomass and chlorine in the oceans. It was used industrially as a refrigerant. Chloromethane was also used to made lead based gasoline, but today it is mainly used as a chemical intermediate in silicone production. [Environmental Science and Technology; v26; 815-16; 1992.] [The Journal of Chemical and Engineering Data; v36; 485-87; 1991.]

Cirrus Clouds - High clouds that are formed entirely from ice crystals. They appear delicate and wispy and can reach a height of 35,000 feet (10,700 meters). Other types of cirrus clouds include cirrostratus and cirrocumulus. Cirrostratus is a thin sheet of cloud that often causes a halo to appear around the sun or moon. Cirrocumulus look like many small tufts of cotton; however, these clouds rarely form. [Journal of Applied Meteorology. v 31, page 370, 1991.] [Journal of the Atmospheric Sciences. v 46, page 2293, 1989.]

Clathrates - Also called gas hydrates, formed by or having molecules which are interlaced in a lattice-like geometrical pattern. [Journal of inclusion phenomena and molecular rec. v 10, page 399, 1991.] [The Journal of Chemical Physics. v 101, 7672, 1994.]

Clean Air Act - The Clean Air Act passed in 1970 and later in November of 1990 made into law established nationwide levels of acceptable air pollution from automobiles, individuals, and industry. The Environmental Protection Agency is responsible for enforcement of standards and regulations of the Clean Air Act. [Sell, N.J.; Industrial Pollution Control: Issues and Techniques 2nd Edition. 1994 John Wiley: New York]

Climate - Determined by the daily weather interactions over many years. Characteristics used in determining climate are temperature, precipitation, humidity, sunshine, and cloudiness, wind, and air pressure. Climatologists describe climate in terms of average temperature and precipitation amounts. [Journal of Climate. v 1, 775, 1988.] [Journal of Climate. v 1, 789, 1988.]

Cloud - Condensed water vapor floating in air. They can take many different shapes due to wind patterns and moisture content. They play an important part in the world's weather because of the water they bring and because of their radiative properties vis a vis global warming. [Chemical and Physical Meteorology. v 41, 2, 1989.] [The Astrophysical Journal. v 333, 617, 1988.]

Cloud Condensation Nuclei (CCN) - Condensed water vapor that is so small that it can only be seen through a microscope. CCN are actually the center of the droplet. Many of these nuclei are tiny salt particles, sulfate or nitrate aerosol, or small particles present in smoke. See dimethyl sulfide. Most droplets measure from 1/2,500 to 1/250 inch (0.01 to 0.1 millimeter) in diameter. [Journal of Applied Meteorology. v 32, 666, 1993.] [Journal of Aerosol Science. v 23 supp. page S865, 1992.]

Coarse Mode Particles - are particles that are roughly defined as having larger than two micrometers in diameter.  They come form sea sprays, volcanoes, crushing or grinding of rocks, wind blown soil, and account for about 95% of the aerosol particles in ambient air. [Journal of Geophysical Research; v113; D05212; DOI:10.1029/2007JD009052]

Column Ozone - The total amount of ozone that is found in a column of air. The majority of this amount of O3 is typically found in the stratosphere. [Journal of Geophysical Research, v 95, 13883, 1990.] [Journal of Geophysical Research, v94, 13883, 1989.]

Condensation - (Gaseous) water vapor that begins to change to tiny water droplets (a liquid state) or ice crystals when the air gets cold enough. This process begins at the dew point. Energy required to vaporize the water is released, about 585 cal/g of water at 20 degrees Celsius. [Physical Review, v 38, 5303, 1988.] [Oceanography; Thurman, Harold; 513; 1994; Macmillan, New York.]

Continental Drift - A term applied to early theories supporting the possibility that the continents are in motion over the Earth's surface. [Scientific American. v 266, 84, 1992.] [Scientific American. v 264, 66, 1991.]

Convection - Process by which, in a fluid being heated, the warmer part of the mass will rise and the cooler portions sink. This is also a a component of the theory for continental drift, in that the circulating movements of crustal materials push the continents apart. [Journal of the Atmospheric Sciences. v 46, 1540, 1989.] [Journal of the Atmospheric Sciences. v 45, 2641, 1988.]

Coriolis Force - A fictional source associated with the earth's rotation. It results in the deflection of all objects not at the equator to the right in the direction of motion in the northern hemisphere and to the left in the southern hemisphere. [Crutzen, Paul and Gradel, T.E. Atmospheric Change: An Earth System Perspective. W.H Freedman and Company, New York. 1993. p.57.]

Cryosphere - The portion of the earth which consists of the ice masses and snow deposits which include continental ice sheets, mountainous glaciers, sea ice, surface snow cover and lake/river ice. Alterations in the extent of snow cover are due to seasonal fluctuations and are interrelated with atmospheric circulation. Sea level and hydrologic cycle variations can affect the volume of water tied up in the glaciers and ice sheets. [Canadian Geographer; v36; 336-350; 1992.] [Canadian Geographer; v37; 86-87; 1993.]

Crystallization - Physical or chemical process or action which results in the formation of regularly-shaped, -sized, and -patterned solid forms known as crystals. [Journal of Chemical Education; v71; 694-696; 1994.] [Science; v261; 1418-1423; 1993.]

Cumulus Clouds - Clouds forming in the troposphere which are vertically formed with flat bases and fluffy, rounded tops. They have often been described as cauliflower-like in structure. They occur at heights of 500-6000 meters in elevation from the earth and most often occur scattered or in dense heaped packs. They are formed due to buoyant upward convection during warm, anti-cyclonic summer weather. [Nature; v363; p584-585; 1993.] [Journal of Atmospheric Science; v50; 3894-3908; 1993.] [Journal of Applied Meteorology; v32; 626-641; 1993.]

Cycle - In the atmosphere or biosphere a sequence of events in repetitive motion in which the final output feeds back into the initial input. Examples of this include biogeochemical cycles, including the nitrogen, carbon, and sulfur cycles in which these species are chemically processed in gas, solid, and solution phase by physical and biological processes which change their form, oxidation state, and physical state. [Living in the Environment; Miller, Tyler; pg 244; 1994; Wadworth; Belmont.] [The Chemistry of the Atmosphere and Oceans; Holland, Heinrich; pg. 1-14; 1978;  

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