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Atmospheric Chemistry Glossary


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DDT - Para-dichlorodiphenyltrichloroethane, first synthesized in 1874 by Othmar Zeidler and later discovered to be a pesticide by Mueller in 1939, was commonly used during the latter half of the second World War (>1942) to kill mosquitoes that carried malaria and yellow fever and it was also used to kill body lice that can transmit typhus. Although initially the success of this pesticide to curb human deaths from mosquito-borne malaria was clear, many problems have been associated with the use of DDT. Some of these problems are the bioaccumulation in the food chain especially fish, decline of smaller animals, build-up in animal fatty tissues, endocrine disruption at low concentration, and softening of bird's eggs; however, acute human toxicity of DTT is so low as to be insignificant. In 1973, the U.S. EPA banned all use of DDT in the US; however, it can still be manufactured in the U.S. but only for use in other countries. DDT is still being used extensively in developing countries, and the World Health Organization supports its use in African countries indoors to fight mosquitoes which are carrying malaria. DDT's transport around the globe in the troposphere is confirmed by the detection of DDT and its oxidative degradation products in air samples over the Arctic Ocean. [Journal of Agricultural and Food Chemistry; v21; 511-519; 1973; DOI:10.1021/jf60188a040] [Environmental Pollution; v157; 1753-1763; 2009; DOI:10.1016/j.envpol.2008.12.026] [Nature; v463;138-139; 2010; DOI:10.1038/463138f] [Atmospheric Environment; v43; 4319-4326; 2009; DOI:10.1016/j.atmosenv.2009.06.003]

Decomposition of Organic Matter - The breaking down (mineralization) of organic matter to produce reduced or oxidized products such as NH3, NOx and CO2 (g) and their subsequent release into the atmosphere; however, much of these decomposition products remain in the soil. [Bioresource Technology; v98; 2526-2532; 2007; DOI:10.1016/j.biortech.2006.09.013] [Bioresource Technology; v97; 1284-1295; 2006; DOI:10.1016/j.biortech.2005.05.023]

Deforestation- Type of "forestry practice" which involves the permanent removal of forests and their undergrowth so that the land can serve another purpose. This practice has had a profound effect on global environmental problems (air pollution, global warming), soil erosion, desertification, sedimentation of water courses, alteration of climate and hydrological cycles, alteration of the atmospheric oxygen and carbon dioxide balance and has caused many species to become extinct, reducing worldwide biodiversity. A common deforestation practice is to simply burn the forest while clearing the land for a seasonal crop. This also creates a large-scale release of carbon dioxide--while at the same time removing carbon storage in the biosphere--further compounding the global warming effect. Estimates of total mass of carbon annually released into the atmosphere from biomass burning are >2 x 1015 g. Since most of the available nutrients are contained in the forest biomass the newly cleared land does not support a crop for more than a few seasons before adjacent land must be deforested. [Geotimes; v39; p.9; 1994.] [Environmental Pollution; v158; 2490-2495; 2010; DOI:10.1016/j.envpol.2010.03.017] [Journal of Geophysical Research; 109(D14); D14S05; 2004; DOI:10.1029/2003JD004423]

Denitrification- A step in the earth's nitrogen cycle which involves the reduction of nitrates (oxidized N) into nitrite, nitrous oxide, ammonia or elemental nitrogen (more reduced N), that is, the conversion of species most often in the liquid or solid phase to chemical species most commonly gaseous. It is carried out by certain forms of denitrifying bacteria in the soil and serves as an important part of the breakdown of dead organisms and the ultimate source of most of the N2 in the atmosphere. It is also responsible for the loss of much of the soil's natural nitrogen and that of synthetic fertilizers. This process is favored most in warm, anaerobic conditions. The opposite process, nitrogen oxidation, nitrification, ultimately leads to the formation of bioavailable nitrates and nitrites in soils. [Science; v261; 1146-1149; 1993; DOI:10.1126/science.261.5125.1146] [Nature; v346; 258-260; 1990; DOI:10.1038/346258a0] [Nature; v351; 135-137; 1991; DOI:10.1038/351135a0] [Field Crops Research; v124; 378-391; 2011; DOI:10.1016/j.fcr.2011.07.009]

Desertification - Simply the change of useful land into a desert environment as cause by natural and/or anthropogenic causes. Factors effecting desertification include droughts; land use, such as grazing and crop use; and climate variations. Desertification influences atmospheric chemistry because the humidity and biospheric gas emissions from the modified biome are also changed by this process [Journal of Arid Environments, v70; 120-136; 2007; DOI:10.1016/j.jaridenv.2006.12.009] [Science; v316; 847-851; 2007; DOI:10.1126/science.1131634] [Applied Geography; v32; 777-786; 2012; DOI:10.1016/j.apgeog.2011.08.005]

Dewpoint - The temperature at which air is cooled enough to reach its saturation point (100% humidity) for a given volume of water vapor in the air. If the air cooling occurs because of adiabatic expansion, clouds are formed; if it is due to contact of the air with a colder object, condensation (known as dew) is formed on the object; and if it is due to mixing of a warmer, moist air parcel with a cooler, dry parcel, fogs and condensation trails are created. Unlike humidity, the dewpoint is not based upon the temperature or pressure of the air, but solely upon the water vapor content. It can be measured using a dew point hygrometer, from the known temperature and relative humidity and by measuring the difference in wet and dry bulb temperatures. It is of importance in predicting fogs, frost, dew and overnight minimum temperatures. [Bulletin of the American Meteorological Society; v74; 1323-1325; 1993.] [Mechanical Engineering; v116; 30; 1994.]

Dibromotetrafluoroethane - A chemical also know as Halon-2402 which has the chemical formula C2F4Br2. It is a known ozone depleting chemical and is listed as a Class I ozone depleting chemical in the United States Clean Air Act amendments of 1990. It is commonly used as a fire extinguishing agent. The reason it has so much ozone depleting potential is because it contains bromine, which has many times the ozone depleting potential of chlorine. [Biochemical Pharmacology; v22; 2843-2851; 1973.] [Science; v272; 1763-1768; 1996.]

1,4-Dichlorobenzene - CH2ClCH2CH2CH2Cl, A compound found in the atmosphere composed of a benzene ring and two chlorine atoms at the 1 and 4 positions. Often found used to make mothballs and as a fumigant, this compound is detected in urban atmospheres and in many human tissue samples. [Journal of Hazardous Materials; v40; 213-235; 1995.] [Atmospheric Environment; v34; 4441-4446; 2000.]

Dichlorodifluoromethane - CCl2F2, This compound, also known as Freon® 12 or CFC-12, is the primary CFC that has been linked to the catalytic destruction of ozone. Even though the compound is found in very small concentrations, its properties make it a significant factor in stratospheric chemistry. CCl2F2 absorbs UV light in the upper stratosphere where it arrives decades after being released in the troposphere. CFCs, which were originally created by Dupont corporation, were used as refrigerants for everything from air conditioning to home refrigerators because they are non-toxic and extremely unreactive (in the troposphere). It is this unreactivity that makes them such a problem for the atmosphere, because they are able to last long enough to make it to the stratosphere, where they cause so many problems. CCl2F2 production, along with all CFCs, has been banned since the mid 1990s, but some scientists believe that the damage has already been done. For further reading see the term ozone. [Crutzen, Paul and T.E. Graedel. Atmospheric Change. W.H. Freeman and Co. NY, 1993, page 45.]

Dichloromethane - CH2Cl2, a clear, colorless organic solvent that has a sweet but mild odor and does not occur naturally in the environment. Its principle use is as a solvent in paint removers and as an aerosol propellant in paints and automotive spray products. In addition, it is used as a blowing and cleaning agent of metal, as a solvent in the production of polycarbonate resins, and in film processing, as well as many other industrial applications. In the food industry, it is used as an extraction solvent for caffeine, spices, and hops. All of these applications result in the release of dichloromethane into the environment, with the primary sources being the industries that manufacture the chemical or use it in production, such as the plastic and synthetics manufacturers, as well as the electronics industry. Upon release of the liquid chemical into the environment, dichloromethane quickly evaporates to a gas, where it is then degraded by photochemically produced products in the air. Because of its reactivity in the troposphere, it is not believed to react with ozone in the upper atmosphere. Despite its solubility in water, it has low acute toxicity to aquatic animals. In animals (as well as humans), dichloromethane is metabolized into carbon monoxide, which has a higher affinity for the heme groups in hemoglobin than does oxygen and results in deprivation of oxygen. Interestingly, dichloromethane has been found to be an antisickling agent in sickle cell hemoglobin. [Proceedings of the National Academy of Sciences of the United States of America, v 73(11); 1976; 4195-4199.] [Science; v176; 295-296; 1972] [Journal of Applied Toxicology; v15; 329-335; 1995; DOI:10.1002/jat.2550150417]

1,3-dichloropropene (C3H4Cl2) is a chemical used as an insecticide fumigant. Because of high volatility of 1,3-dichloropropene it is certain that a signicant portion finds it way into the atmosphere during application and both cis- and trans-1,3-dichloropropene  react with ozone and hydroxyl radical. [Archives of Environmental Contamination and Toxicology, v13, 691-700, 1984.]

Diethyl Ether (Ethoxy Ethane) - A colorless liquid that was first used in 1842 as an anesthetic in surgeries by inhalation. This liquid is highly flammable
and has volatile properties. It is commonly referred to simple as ether. Ethoxy ethane is prone to peroxide formation, and can form explosive diethyl ether peroxide, especially in old storage vessels. Ether peroxides are higher boiling and are contact explosives when dry. Symptoms of severe exposure may include coughing, chest pains, difficulty in breathing, nausea, headache, vomiting, or death. [Analytical Chemistry; v70; 5213-5221; 1998.] [Journal of Chemical Technology & Biotechnology; v75; 9; 2000.]

Diethyl Ketone - A volatile organic compounds whose formula is C5H10O. It is released from combustion exhaust and solvent use. This is a compound that undergoes photolysis around the wavelengths of 302-320 nm and produces an acyl radical, CH3CH2C(=O). That reactive species reacts with molecular oxygen to form a peroxide which can oxidize NO to NO2 :

CH3CH2C(=O)CH2CH3 + hv ---> CH3CH2C(=O). + CH3CH2.
CH3CH2C(=O). + O2 ---> CH3CH2C(=O)O2.
CH3CH2C(=O)O2. + NO ---> NO2 + CH3CH2CO2.

And finally the acylate radical CH3CH2CO2. can further oxidize NO to NO2, providing even more ammunition to make ozone while the sun shines (see nitrogen dioxide and ozone). [Subramanian, M.S.; Environmental Chemistry Analysis; Module 3.3 Organic Air Pollutants; Department of Chemistry; India Institute of Technology, Madras, India] [Atmospheric Environment; v34; 2063-2101; 2000; DOI:/10.1016/S1352-2310(99)00460-4] [Laity, J.L.; Burstain, I.G.; Appel, B.R.; "Photochemical Smog and the Atmospheric Reactions of Solvents"; Chapter 7; in Solvents Theory and Practice; 1773; American Chemical Society; Washington D.C.; pp95-112; DOI:10.1021/ba-1973-0124.ch007] [Atmospheric Environment; v40(S1); 81-91; 2006; DOI:10.1016/j.atmosenv.2005.10.070]

Diffraction - The process where a light wave's direction is changed due to the wave coming into contact with a different medium. In the atmosphere this especially involves particle diffraction of sunlight, diffraction that causes rainbows, cloud colors, and is the reason why, in part, the sky is blue and sunsets red. [Optics and Lasers in Engineering, v35; 773-782; 2007.] [Journal of Quantitative Spectroscopy and Radiative Transfer; v110; 844-878; 2009; DOI:10.1016/j.jqsrt.2009.02.035]

1,2-Dimethylbenzene – A colorless liquid with a sweet odor that is classified as a volatile organic compound (VOC) found largely in the atmosphere in high-traffic urban areas 1,2-dimethylbenzene is primarily emitted into the atmosphere through exhaust and emissions from gasoline engines along with industrial emissions from processes such as coal distillation and petroleum refining. This compound is a threat not only in the atmosphere but also to water quality and land surfaces. High concentrations of 1,2-dimethylbenzene in the atmosphere can lead to irritation of the eyes, nose, throat, and can also cause severe breathing problems. [Environmental Pollution; v101; 221-230; 1998; DOI:10.1016/S0269-7491(98)00048-7]

Dimethyl Sulfide - CH3SCH3, released by bacteria on the continents and in the oceans. Oxidized in the marine atmosphere to partially form cloud condensation nuclei and this may effect the formation of clouds over the oceans. [Nature; v326, 655, 1987.] [Nature; v237, 452, 1972.]

Dinitrogen Pentoxide - N2O5, a compound that contributes to ozone depletion during springtime in the Antarctic. This occurs because ozone converts some nitrogen dioxide radical to nitrogen trioxide radical, which combines with other dinitrogen radicals to produce dinitrogen pentoxide. The reaction is reversible except in the presents of stratospheric liquid droplets where nitric acid occurs. This reaction ties up the nitrogen dioxide radical allowing more chlorine atoms to be present in the active form. [Atmospheric Environment; v38; 5837-5848; 2004.]

Dioxins- Family of 75 different toxic chlorinated hydrocarbons formed as by-products in chemical reactions involving chlorine and hydrocarbons, usually at high temperatures. The "premier" and probably most toxic member of the dioxin family is 2,3,7,8-Tetrachlorodibenzo-p-dioxin. Though these compounds have relatively low vapor pressures and poor solubility in water, they cycle from aquatic environments--where they have been deposited from waste incineration, wood burning, pulp bleaching, smelting, etc.---into the atmosphere in a series of small steps, staying airborne, and atmospheric mobile, for short periods of time. Dioxins have been found in some organisms on all the earth's continents. [Miller Jr., G. Tyler. Living in the Environment. 9th ed. Wadsworth Publishing Company: New York; 2002.] [Environmental Pollution; v119; 151-161; 2002.] [Science; v313; 1555; 2006.]

Dispersion - The scattering of colors of visible light from white light by refraction off or passing through different media. [Optics & Laser Technology, Vol. 39, 913-917, 2007.]

Disproportionation-A reaction in which an element is oxidized and reduced. This is how stable molecules are made from radicals. [Journal of Physical Chemistry A; v103n50; pages 11212-11220; 1999] [Inorganic Chemistry; v41n23; pages 6099-6106; 2002.]

Dissociation - Process in which large chemical species break down into smaller, usually charged subunits, like a molecule breaking down into the ions that form it. [Fluid Phase Equilibria, Vol. 253, 98-107, 2007.]

Dissolution- The transfer of gas to the surface of a water droplet from the bulk atmosphere, and the gas mixing within the droplet. [Air Composition and Chemistry; v2; p91; 1986].

Diurnal Ozone Concentration - The ozone concentration in the troposphere is directly related to the pollutants that are in the air and the time of day. For example, during the early hours of the day many pollutants are released into the air. As the day progresses, the sun becomes more overhead and the concentration of the sunlight increases. This solar radiation causes chemical reactions to occur and the primary pollutants decrease while the concentration of ozone increases. Eventually the ozone breaks back down and the process is ready to proceed the next day. [Regulation; 13(1); 31-40; 1990.] [Atmospheric Environment; v38; 2361-2371; 2004.]

Dobson Units - Measurement unit for determining the total amount of ozone present in a vertical column of air above the surface of the earth. An air layer at atmospheric pressure of 1013 hPa and temperature of 298 K which measures 1 mm in thickness and is equivalent to 100 dobson units. [Science; v266; 217; 1994.]

Doldrums- Calm, light winds, or squalls lying along the length of the equator. Winds which are part of the general circulation of the atmosphere, which are driven by the input of solar energy and modified by the rotation of the Earth. It is here that 17th and 18th century sailing ships had the most trouble making way and lack of fresh water or food sometimes spelled disaster [Air Composition and Chemistry; v2; p13; 1986.]

Droughts - Extensive periods of time where a region suffers from lack of rain, causing dehydration for animals and plants, often resulting in crop failure. Sequential droughts during the 1930s in the United States were extremely damaging to the Great Plains, made worse by poor land management practices. [Riebsame, W.E.; S.A. Changnon, Jr.; and T.R. Carl; 1991; Drought and Natural Resources Management in the United States: Impacts and Implications of the 1987–89 Drought; Westview Press; Boulder, Colorado] [Journal of Hydrology; v391; 202-216 ; 2010; DOI:10.1016/j.jhydrol.2010.07.012] [Journal of Hydrology; v401; 190-202; 2011; DOI: 10.1016/j.jhydrol.2011.02.020]

Dry Adiabatic Lapse Rate - Rate at which unsaturated air cools as it travels vertically, provided that all temperature change is adiabatic (without heat exchange), and no condensation occurs. In dry air it can be approximated as 9.8 degrees Celsius per km of rise. It can be used as a basis of comparison for actual temperature profiles of air and can help predict smoke stack gas dispersion characteristics. Contrast with saturated adiabatic lapse rate which is something less than 9.8 degrees/km of rise because of the release of heat at the air packet cools and water vapor condenses. [Journal of Atmospheric Sciences; v51; 1237-1243; 1994.] [ Journal of Applied Meteorology; v33; 65-73; 1994.]

Dry Deposition - The transfer of trace species (gases or particles) from the atmosphere to surfaces as a consequence of molecular diffusion, brownian diffusion, or gravitation settling, in the absence of active precipitation. The term refers to the transfer process and not to the surface themselves, which may be moist. [Graedel, T. E. and Paul J. Crutzen. Atmospheric Change: An Earth System Perspective. W. H. Freeman and Company: New York, 1993.]


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Ecliptic - The plane of orbit of the earth around the sun. An animation showing this process is available on its own page. [Icarus; v153; 111-129; 2001.]

Ecology - Branch of biology which focuses on the relationships among various species and among the species and their environments. The basic units for study are the species (all the organisms which are capable of interbreeding), population (all of the members of a species occupying a certain geographical area) and community (number of populations interacting within a certain area). The emphasis in environmental science, however, is on the processes of energy flows and nutrient cycles within these communities and ecosystems and involves such ideas as species abundance, biodiversity, complexity, trophic (feeding status) levels, ecological niches, and structure of communities. [Ecology; v75; 2430-2437; 1994.][Science; v260; 1472-1481; 1993.]

Eddy Diffusion - The exchange of gaseous components of the atmosphere in a turbulent flow by rapid mixing of fluid eddies. [Journal of Marine Research; v. 52; p.129-148;1994.] [Journal of Atmospheric and Terrestrial Physics; v. 54, 148; 1992.]

Efflorescence - The reverse process of deliquescence; the drying of a salt solution when the vapor pressure of the saturated solution of a substance is greater than that of the ambient air. [Atmospheric Change: an Earth system perspective; p429; 1993; Freeman Press.]

Effusion - The movement of gas molecules through an opening that has relatively large holes. [American Journal of Physics; v57; p1116; 1994.] [Journal of Physical Chemistry; v93; p5316; 1989.]

E-Folding Lifetime - The time required for the concentration of a gas to decrease by 1/e of its original concentration due to a chemical reaction or other sink. [Journal of American Chemical Society; v124; 1524-1531; 2002.]

Electrolysis - A method of using electricity to break chemical bonds or cause electron exchange. An electric current passes through an electrolyte causing ions to move toward the electrodes. The positively charged electrode, called the anode, attracts anions and causes them to be oxidized. The negative electrode is called the cathode. It attracts cations which are then reduced. The electrical energy applied to the ionic solution causes a non-spontaneous process to become spontaneous. Electrolysis of water produces molecular hydrogen and molecular oxygen. [Journal of Power Sources; v164; p9-16; 2007.] [International Journal of Hydrogen Energy; v25; 415-423; 2000.]

Electromagnetic Wave - A phenomenon that can carry energy through space and is created by the vibration of an electrical charge, which is caused by disturbances in electromagnetic fields. Examples of electromagnetic waves include infrared, visible, microwaves, and x-rays. Forms of electromagnetic waves that can be seen by humans we call light. [Journal of Quantitative Spectroscopy and Radiative Transfer; v79-80; 1189-1198; 2003.] [Bioelectrochemistry and Bioenergetics; v47; p283-290; 1998.]

Electron Capture Detector - One of the most sensitive gas chromatographic detector for halogen-containing compounds like chlorofluorocarbons. Here's an animation. James Lovelock's early work with this detector led to the discovery that anthropogenic chlorofluorocarbons used most heavily in the Northern hemisphere were very long-lived and therefore well-mixed throughout the troposphere. Later work by Rowland and Molina suggested that CFCs also diffused into the stratosphere where their chlorine atoms could by freed by photolysis-CFC bond breaking by UV light. The result of this is the destruction of ozone molecules in the important ozone layer of the stratosphere. [A Journal of Chromatography; v952; 173-183; 2002.]

Electrostatic Precipitator - A device that reduces pollution from smokestacks. It gives the particles in smoke an electrical charge. The charged particles are then collected on filters that have the opposite charge and the particles are thereby removed from the emission stream. [Fleisher, Paul. Ecology A to Z. Dillon Press, New York. 1994. p. 70.]

El Nino - A condition caused by the decrease in atmospheric pressure over the Eastern Pacific Ocean, weakening the prevailing westerly winds and resulting in warm waters and less nutrient replacement from cold, deeper waters into the Eastern Pacific along the coast of South America. This event creates strange weather patterns worldwide sometimes causing flooding in California and droughts in South America simultaneously. The effect gets it name from the Spanish for the Christ Child--the little one--because it is experienced in December by the local fisherman off the western coast of South America as a poor fishing season. [Scientific American; v. 259, 20-25; 1988.] [The Chronicle of Higher Learning; v. 40, p.A8; 1994.]

El Nino-Southern Oscillation (ENSO) - The relationship of the El Nino conditions and the Southern Oscillation pattern (The Walker Circulation). A high pressure over the Pacific Ocean and low pressure over the East Indies causes heavy rainfall across the Pacific, rise in the sea level and increased surface temperatures. [Journal of Atmospheric Sciences; v. 51, 1115; 1994]. [Science; v. 264, 72-74; 1994.]

Elliptic - An object having the shape of an ellipse: a squashed or elongated circle. The sun follows an elliptic path across the sky. [Earth, Moon, and Planets; v. 60, 47; 1993.] [Astrophysics and Space Science; v. 162, 107; 1989.]

Emission - A substance discharged into the air, especially by an internal combustion engine. The majority of the substance consists of un-burned hydrocarbons that react in the atmosphere to produce ground-level ozone. Urban air gases consist of nitrogen oxides, reactive organic gases, carbon monoxide, and sulfur oxides. Emission standards from EPA are just about everywhere and air pollutants are controlled from both industrial and automobile sources. [Journal of Environmental Economics and Management; v. 25, 177-195; 1993.] [Science; v. 26; 5151, 1255-1257; 1994.]

Emission Spectrum - a spectrum of electromagnetic radiation containing narrow spectral lines from an element. [Chambers Nuclear Energy and Radiation Dictionary; p.152, W&R Chambers Ltd.; New York; 1992.][Nature; v236; 444 - 445; 1972; DOI:10.1038/236444a0]

Emissivity - The efficiency of a body's ability to absorb and reemit radiation compared to the emissivity of a blackbody at the same temperature. Emissivity ranges from 0 to 1, with one being a blackbody and less than 1 for all other materials. All bodies with a temperature above 0 K emit radiation. [Applied Surface Science; v253; 778-783; 2006.]

Endothermic - A chemical reaction in which heat is absorbed from the surrounding environment. [Physical Chemistry; v. 319, 608; 1991.] [Journal of Geophysical Research; v. 99, 15919; 1994.]

Energy - The ability of a system to do work. Some forms of energy include kinetic (motion), potential (location), thermal (heat), gravitational, and electrical. In chemistry, energy is required to form and break bonds of molecules. Common units of energy are the calorie and joule. According to the Law of Conservation of Energy, energy can neither be created nor destroyed, only transformed. [Applied Surface Science; v253; 4966-4969; 2007.]

Enhanced Greenhouse Effect - Increasing the concentration of the trace gases in the air that absorb thermal infrared light, i.e. greenhouse gases, will result in more infrared light redirected to the earth causing an increase in temperatures. [Baird, Colin; Environmental Chemistry; 2nd ed.; New York: W.H. Freeman, 1999.]

Enthalpy - A thermodynamic variable that is a system's internal energy plus the product of its pressure and volume: H = E + PV. [Chemistry - The Molecular Nature of Matter and Change; Silberberg, Martin; Ed. James M. Smith; p. 228; 1996; Mosby-Year Book, Inc.; St. Louis, Missouri.] [Oil & Gas Journal; v93; 62-63; 1995.]

Entrainment zone - The layer between the convective mixed layer and the free troposphere that is caused by a temperature inversion. This inversion inhibits the rising of heat and gases, trapping pollutants closer to the ground. [Atmospheric Environment; v36; 2997-3008; 2002.] [Atmospheric Research; v69; 147-163; 2004.]

Environmental Protection Agency - (U.S. EPA) An American federal agency formed in 1970 during the Nixon Administration in order to protect human health and the environment. The EPA today focuses on the atmosphere, fresh and ocean waters, and soil quality within the United States. [Journal of Chromatography A; v643; 117-143; 1993; DOI: 10.1016/0021-9673(93)80546-K] [Atmospheric Environment; v38; 3101-3106; 2004; DOI: 10.1016/j.atmosenv.2004.03.001]

Equatorial Rain Forests - An area located near the equator worldwide, covering seven percent of the earth's surface, characterized by high precipitation, absent or short dry season, high tree and vegetative growth rates, high humidity, high photosynthetic rates and extreme biodiversity. The equatorial rain forests produce much of the oxygen in the Earth's atmosphere and absorbs large quantities of carbon dioxide from the air. (See deforestation.) [The Quarterly Review of Biology; v68, 560; 1993.] [The Journal of Tropical Ecology; v9, 364; 1993.]

Equinox - Twice during the year, September 21 and March 21, the length of day and night are equal because the tilt of the Earth's axis (in relationship to the sun) is nullified and both the Northern and Southern Hemispheres receive equal quantities of sunlight. An animation showing this is here. [Natural History; v103, 26-27; 1994.] [Astronomy; v20, 52-54; year?.]

Ethane - CH3CH3, a hydrocarbon found in the atmosphere whose primary fate is to react with free radicals such as chlorine and nitrous oxide. This reaction would prevent these radicals from reacting with ozone which is needed in the stratosphere to block ultraviolet light from reaching the surface of the earth. [Journal of Colloid and Interface Science; v273; 313-319; 2004.]

Ethanol - Also known as ethyl alcohol or alcohol, (C2H5OH) is an oxygenated hydrocarbon that can be burned as a fuel, or blended into gasoline. Thought of as an alternative fuel and clean fuel, ethanol is a renewable energy source that is made from corn or other grains, for instance in Brazil from sugar cane. If blended into gasoline, ethanol helps with the combustion process and therefore less unburned hydrocarbons form. Ethanol blended fuels competed with methyltertbutylether (MTBE), but because of the cost and the fact MTBE can be shipped through existing pipelines, MTBE was chosen. MTBE is now being banned because of its ability to travel in ground water and the bad taste it imparts to drinking water. Because of this, ethanol is once again being put back into gasoline. The process of producing ethanol from grain requires energy. The question is: how much? Furthermore since ethanol is "less energy dense" than gasoline the same volume will produce less energy. [Sensors and Actuators B: Chemical; v123; 89-93; 2007.]

Ethyl Acrylate - C5H8O2, also known as ethyl ester 2-propenoic acid, a highly volatile liquid used in the production of polymers. It is soluble in most organic solvents and only slightly soluble in water. The gas phase will react with hydroxyl radicals, chlorine atoms, and ozone. When reacting with ozone it can lead to formaldehyde and other highly oxygen-containing compounds such as ethyl glyoxylate.  [Journal of Physical Chemistry A; v114; 83768383; 2010; DOI:10.1021/jp104451v]

Ethylbenzene- C8H10, Colorless, flammable liquid with an aromatic odor, it is found in coal tar, petroleum, as well as in manufactured products like inks, insecticides, and paints. Ethylbenzene is also used to make styrene. It is during the manufacturing process that ethylbenzene becomes an airborne hazard. It takes about 3 days for ethylbenzene to breakdown into other chemicals. Exposure to ethylbenzene causes dizziness, throat and eye irritation, tightening of the chest, and a burning sensation in the eyes. The Occupational Safety and Health Administration (OSHA) has set an occupational exposure limit of 100 ppm of ethylbenzene for an 8-hour workday for a 40-hour workweek. [Journal of Chromatography; v1066; i1-2; p 27-32; 2005] [Journal of Chromatography; v1069; i2; p 235-244; 2005.]

Ethylene Oxide - C2H4O, An organic compound that is colorless & flammable at room temperature with a sweet odor. Its atmospheric importance is that is can cause irritations of the eyes and mucous membranes and problems in the functions of the brains and nerves at high gas phase concentrations. Exposure to this is by emissions into the air by uncontrolled venting, automobile exhaust, breathing contaminated air from smoking or secondhand smoking.

2-Ethyltoluene - It is an aromatic hydrocarbon occurs naturally at low levels in crude oil and is usually produced in the processes of making gasoline via catalytic reforming. It is a clear, water-insoluble liquid with the smell of paint thinner. The majority of ethyltoluene is used as a petrol constituent in the C9 fraction produced from petroleum refining, which also contains 1,2,4-trimethylbenzene and other trimethylbenzenes (see 1,2,4 trimethylbenzene). 2-Ethyltoluene is also a volatile organic compound VOC which can contribute to the formation of harmful ground level ozone formation. Releases of 2-ethyltoluene are directly to the air from fugitive emissions from petroleum refining, and car exhausts. As a VOC, 2-ethyltoluene can be involved in reactions with other air pollutants that can form ground-level ozone, which can damage crops and materials as well as having negative effects on human health. [Atmospheric environment; v37; 2485-2496; 2003; DOI:10.1016/S1352-2310(03)00177-8]

Eustatic Changes - A consistent change in the sea level that affect oceans, throughout the world. [Marine geology; v102; 239; 1991.] [Geology; v19; 1209; 1991.]

Evaporation - The process of the change in the state of a liquid or solid to a gas or vapor. Vanishing of the surface of a liquid to the atmosphere. [The Journal of physical chemistry; v92; 5864; 1988.] [Journal of colloid and interface science; v126; 181; 1988.]

Evapotranspiration - The total water loss due to the transpiration of vegetation plus the evaporation from the soil; higher climatic temperatures result in a higher evapotranspiration rate. [Miller, Raymond W. et al., Soils In Our Environment. Prentice Hall, Englewood Cliffs, NJ, pg. 614.] [Agricultural and Forest Meteorology; v139; 154-163; 2006.]

Exothermic - A chemical reaction associated with energy, or heat that is released into the surroundings. [Geophysical research letters; v21; 2413; 1994.] [Journal of material science letters; v13; 868; 1994.]

Extinction Coefficient - A measure of the rate of the reduction of transmitted light through a substance. [Journal of Physics D: Applied Physics; v23; 1735; 1990.] [Applied Optics; v30; 4824; 1991.]

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