2015 Version

Atmospheric Chemistry Glossary


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Lachrymators - Any substance that causes the eye to tear, redden, and or swell; eye irritant examples include formaldehyde, brombenzyl cyanide, chloroacetophenone, and dichlorodimethyl ether [Journal of Forensic Science; v 47; pages 44-51; 2002] [Journal of Chromatography; v80; 155-160; 1973: DOI:10.1016/S0021-9673(01)85327-9]

Lapse Rate - The rate of decrease of temperature with increasing altitude in the atmosphere. If heat is neither gained nor lost from the air parcel under consideration, then the lapse rate is said to be adiabatic. For air parcels of differing water content this value is different. In the troposphere, these two values are generally inversely proportional: increasing altitude means a lower temperature until the tropopause is reached. When altitude increases and temperature decreases, the lapse rate is considered positive, and for unsaturated tropospheric air this is approximately 9.8 degrees C/km; however, in an inversion layer the atmospheric lapse rate is negative, that is, the atmosphere's temperature warms with increasing altitude. [Atmospheric Change: An Earth System Perspective, T.E. Graedel and Paul J. Crutzen, W.H. Freeman and Co., New York, 1993, p.431.] [Atmospheric Research; v96; 273-285; 2010; DOI: 10.1016/j.atmosres.2009.09.002] [International Geophysics; v99, 15-52; 2011; DOI:10.1016/S0074-6142(10)09908-0]

Latent Heat - If a change of state occurs from gas to liquid or liquid to solid, internal energy in the form of heat is released. If a change of state occurs from solid to liquid or liquid to gas, heat is required. Different compounds absorb and release different amounts of latent heat. Water releases nearly 600 kilocalories for each kilogram of water condensed. [Journal of Applied Meteorology; v33; 477-489; 1994; DOI:10.1175/1520-0450(1994)033<0477:EOSALH>2.0.CO;2] [A Field Guide to the Atmosphere; V. Schaefer, J. Day; page 75; 1981; Houghton Mifflin Company; Boston.] [Air, The Nature of Atmosphere and the Climate; Michael Allaby; pages 59-60; 1992; Facts on File; New York.]

Lithology - The branch of mineralogy that deals with the study of rocks and their composition. [Oil and Gas Journal; v91n13; 81-84; 1993.] [Dictionary of Science; R.K. Barnhart; page 364; 1986; Houghton Mifflin Company; Boston.] [Journal of Asian Earth Sciences; v41; 477-493: 2011; DOI:10.1016/j.jseaes.2011.01.019]

Lithosphere - The outer, rigid shell of the Earth, situated above the asthenosphere and containing the crust, continents and plates. [Atmospheric Change: An Earth System Perspective, T.E. Graedel and Paul J. Crutzen, W.H. Freeman and Co., New York, 1993, p.431.] [Earth and Planetary Science Letters; v80; 145-155; 1986; DOI:10.1016/0012-821X(86)90028-2]

LPG (Liquid Petroleum Gas) - is a mixture of short hydrocarbons with most of the volume being propane and butane. LPG is considered an alternative fuel that burns cleaner than gasoline because of the very short hydrocarbon chains that tend to not produce a high volume of CO2 (when compared to the energy harvested) or NOx radicals. LPG is now being found in the air in the unburned state most likely from leaking pipes and tanks; in this physical state LPG is now being seen a contributor to urban air pollution. [Respiratory Medicine; v100; 1208-15; 2006; DOI:10.1016/j.rmed.2005.10.020]

London Type Smog - A combination of several gases and particulate matter that forms during a cover of fog or in the event of a low lying temperature inversion. The gases present include sulfur dioxide as a result of the burning of coal for use as energy, and the particulate matter included calcium sulfide as a result of acid deposition. In London England, in 1952, over a four day period, a temperature inversion trapped smoke and sulfur dioxide at dangerous levels, >4 mg/m3 and >1.3 ppmv respectively, both ten+ times the normal levels. Hundreds to thousands of city residents dies because of this event. [Science of the Total Environment; v334-335; 435-445; 2004; DOI:10.1016/j.scitotenv.2004.04.047] [Journal of Aerosol Science; v31; Supplement 1; 578-579; 2000; DOI:10.1016/S0021-8502(00)90589-5]

Long Range Transport - This type of transport involves air pollutants in the atmosphere. If the pollutants are light enough---such as gases or low density particles---or are propelled high enough in the atmosphere, they may be picked up in horizontal winds and transported long distances. If the air pollutants travel within the moving air mass greater than 100 kilometers, than this is considered long range transport. In the spring of 2011, after the nuclear accident following the March 2011 9.0 magnitude earthquake off the Japanese coast, radioactive particles released from the Tokyo Electric Power nuclear reactor complex in the Fukushima Prefecture, Japan were detected on the east coast of the United States at levels that were slightly above background. [Atmospheric Environment; v42; 7579-89; 2008; DOI:10.1016/j.atmosenv.2008.06.051] [Applied Radiation and Isotopes; v64; 93-100; 2006; DOI:10.1016/j.apradiso.2005.07.006]


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Magnetosphere - A volume outside of the Earth’s atmosphere that is a magnetic field. For the Earth, this field is dipolar, acting like a large bar magnet. This field surrounds Earth like a giant bubble, helping to block the particle- and charge-rich solar wind. It is because of the magnetosphere that auroras are seen at the poles. [Advances in Space Research; v47; 1508-1522; 2011; DOI: 10.1016/j.asr.2010.12.022] [Planetary and Space Science; v59; 482-494; 2011; DOI: 10.1016/j.pss.2010.07.021]

Mercury - Mercury is a toxic heavy metal released into the atmosphere, most significantly, through the burning of coal in coal-fired power plants and from Hg-cell chloralkali plants where Hg acts as a flowing electrode used to reduce Na+ to Na0 in an amalgam. While levels of mercury in the atmosphere aren't directly toxic, mercury deposition into lakes and rivers leads to elevated levels of mercury in these organisms, which can eventually be transmitted to humans through the eating of fish and other organisms which bioaccumulate Hg and other toxic heavy metals. Long range transport has moved this element---released in combustion processes---to all of the continents on the planet. Mercury is methylated biochemically in the biosphere into a much more toxic form, methyl mercury, CH3HgX, where X can be variously -CH3, -OH, or -Cl or other halogens. [Science; v322; 1316-1319; 2008; DOI:10.1126/science.322.5906.1316] [Science; v176; 1232-1233; 1973; DOI:10.1126/science.176.4040.1232] [Journal of Environmental Management; v83; 80-92; 2007.] [Science of The Total Environment; v368; 236-247; 2006; DOI:10.1016/j.scitotenv.2005.09.092]

Mesopause - The upper limit and the coldest portion of the mesosphere. The transition zone between the mesosphere and the thermosphere. [Journal of the Atmospheric Sciences; v49n6; 477-496; 1992.] [Introduction to Meteorology; F.W. Cole; p. 7; 1980; John Wiley and Sons: New York.] [Journal of Atmospheric and Solar-Terrestrial Physics; v68; 10611074; 2006; DOI:10.1016/j.jastp.2006.01.011]

Mesosphere - In the atmosphere, the region immediately above the stratosphere and immediately below the thermosphere. The mesosphere begins about 50 kilometers high at the stratopause and ends about 80 kilometers high at the mesopause. The temperature in the mesosphere decreases sharply with increased altitude. [Journal of the Atmospheric Sciences; v49n24; 2353-2371; 1992.] [Introduction to Meteorology; F.W. Cole; page 7; 1980; John Wiley and Sons New York.]

Mesozoic Period - Period spanning from 225 to 65 million years before present (Myr BP), this period was marked by widespread warmth of the planet's surface, especially in the higher latitudes. During this time the continents were joined in a single supercontinent. This situation most likely facilitated the meridional transport of heat by ocean currents, thus resulting in an even distribution of global heat. [Earth-Science Reviews; v48; 183-210;1999; DOI:10.1016/S0012-8252(99)00048-3]

Metastable State - A object that returns to its original position after force is applied. [Vibrational Spectroscopy; v43; 53-63; 2007.][Journal Geophyical. Research; 91(D13); 14533-14537; 1986.]

Meteorology - The science of the atmosphere and its direct effects upon the earth's surface. Meteorology is especially concerned with how atmospheric conditions effect the weather. [Science; v146n23; 380-381; 1994.] [Introduction to Meteorology; F.W. Cole; page 2; 1980; John Wiley and Sons New York.]

Methane - CH4, a colorless, odorless, flammable, greenhouse gas. It is the simplest of all hydrocarbons with a formula of CH4. Methane is released naturally into the air from anaerobic environments such as marshes, swamps, and rice fields, and from symbiotic microbes in the guts of ruminant animals (such as cattle, sheep, and camels), and sewage sludge. Methane is released from methane producing bacteria (methanogens) that live in these anaerobic places. Methanogens in termite guts are the source of methane released by termites. The discovery that termites may be a significant source of atmospheric methane is attributed to work by Patrick Zimmerman and his research group members at the National Center for Atmospheric Research in Boulder Colorado (see reference immediately below and papers in the scientific literature). 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. [Solar Energy; v52n6; 467-477; 1994.] [Air, The Nature of Atmosphere and the Climate; Michael Allaby; pages 39,40; 1992; Facts on File; New York] [Dictionary of Science; R.K. Barnhart; page 398; 1986; Houghton Mifflin Company; Boston. DOI:10.1126/science.1141038]

Methane Flux - The (continuous) flow of methane from one place in the atmosphere to another. It is usually measured as a rate of flow across a given area where methane is produced; for instance, the average amount of methane being released from a rice field of a specific area every hour would be considered the methane flux rate for that field. [Dictionary of Ecology and Environmental Science; Henry W. Art; 1993; Henry Holt and Company; New York.] [Testing of Hydrocarbon Emissions From Vegetation and Methodology for Compiling Biogenic Emission Inventories; Patrick R. Zimmerman; National Center for Atmospheric Research; P.O. Box 3000 Boulder, Colorado 80303.]

Methanesulfonic Acid (MSA) - This may be a significant component of atmospheric aerosol particles that form from the atmospheric oxidation of dimethylsulfide (DMS), when this DMS is produced by phytoplankton. These aerosol particles can lead to the formation of cloud condensation nuclei, water droplet formation, and hence clouds and storm formation. This therefore may contribute to the turbulent mixing of oceanic surface waters and subsequent upwelling of nutrients that feed those microorganisms (a positive feedback cycle). It is thought that increased emissions of dimethylsulfide, and subsequent methanesulfonic acid over the oceans from an increase in sea water temperature may have a negative feedback on global warming by increasing cloud formation; although the net effect of clouds on global warming is very unclear at this point. [Baird, Colin. Environmental Chemistry, p. 179, W.H. Freeman and Company, 1995.]

Methanol - CH3OH, Classified as a VOC and introduced naturally to the atmosphere by flowering plants though plant structures and metabolic processes and by biological decomposition product of biological wastes and sewage. Also released into the atmosphere as an evaporated solvent. When oxidized it forms formaldehyde and ozone. [Environmental Science & Technology; v39; 1724; 2005.] [Journal of Physical Chemistry; v109; 1603; 2005.]

Methyl Bromide - CH3Br, this halocarbon is released, to a degree, naturally from the oceans, but is more commonly released from its anthropogenic use as a soil fumigant or pesticide. Methyl bromide is persistent enough to reach the stratosphere where it photochemically decomposes to yield atomic bromine (radical) and proceeds to destroy stratospheric ozone in the same manner as the atomic chlorine radical. On an atom-for-atom basis, stratospheric bromine is more efficient at destroying ozone than is chlorine because the HBr reservoir species is more photochemically active than HCl; however, there is much less of hydrogen bromide in the stratosphere. Recent data suggest that since 1998 atmospheric concentrations have dropped 13% due the CH3Br use limitations mandated by the Montreal Protocol [New York Times Aug. 16, 2003] [Baird, Colin. Environmental Chemistry. (1999) W.H. Freeman, New York.]

Methyl Chloride - CH3Cl, this compound supplies chlorine to the stratosphere by occasional volcanic eruptions and by tropospheric to stratospheric transport. Methyl chloride is also produced by seaweed. The natural chlorine content of the stratosphere as a consequence of these sources is about 0.6 ppbv. [Graedel, T. E. and Paul Crutzen. Atmospheric Change: An Earth System Prospective. W.H. Freeman and Company: New York, 1993: 143.]

Methyl Chloroform - CH3CCl3, a synthetic organic compound that has been used as a substitute for earlier solvents that contributed to air pollution. Methyl chloroform is now known to cause destruction to stratospheric ozone and is scheduled to be phased out by the year 2005. [Applied and Environmental Microbiology; v60; 3329-3335; 1994.] [The Green Encyclopedia; Irene Franck, David Brownstone; page 192; 1992; Prentice Hall: New York.]

Methylcyclopentadienyl Manganese Tricarbonyl - See MMT.

Methylcymantrene - See MMT.

4-Methyl-2-Pentanone (Methyl Isobutyl Ketone) – Considered a volatile organic compound (VOC) which contributes to photochemical smog in the presence with other VOCs. In the Clean Air Act Amendments of 1990 methyl isobutyl ketone was added to the list of hazardous air pollutants because it is created in urban settings by photochemical reactions. This compound is a colorless flammable liquid, primarily used as a solvent for protective surface coating such as for acrylic enamels and lacquers. It is also used in solvent extractions in the dry-cleaning industry and is regulated by the occupational safety and health administration since exposure can experience nausea, burning eyes, weakness, headaches, and more significantly, damage to the liver and the kidneys. [Regulatory Toxicology and Pharmacology; v52; 180-188; 2008; DOI:10.1016/j.yrtph.2008.08.007]

Methyl Radical - CH3. is formed, along with water, from the reaction of methane (CH4) and the hydroxyl radical (OH.). This begins a series of reactions that eventually produces atmospheric ozone (O3). [Journal of Chemical Information and Computer Sciences; v39; 1999.] [Journal of Physical Chemistry A; 106; 2002.]

Methyl Tertiary Butyl Ether - See MTBE.

Midocean Ridge - A major, elevated, linear feature of the seafloor, consisting of many small, slightly offset segments, with a total length of 200 to 200,000 km. This type of plate boundary occurs in a divergence zone, which is a site where two plates are being pulled apart and new oceanic lithosphere is being created. [Tectonophysics; v386; 223-242; 2004.]

Mie Scattering - Processes by which particles of similar size and electrical characteristics separate or disperse different wavelengths (read colors) of light. First described by Gustav Mie in 1808. Since the sun's visible spectrum contains a mixture of (traditionally ordered) red, orange, yellow, green, blue, indigo, and violet colors, these wavelengths are differentially scattered by particles as they travel through the atmosphere. Red--longer wavelength--light is scattered not much and blue--shorted wavelength--light is scattered much more. This is why the sky appears blue: the sun's blue light is scattered back towards your eyes from atmospheric particles so when you look up--that is, away from the sun, the light you see is light scattered to your eye from atmospheric particles. (You might ask yourself why the sky--viewed at an off angle from the sun--isn't black instead of blue.) Mie scattering is also the reason why sunsets appear red: the sun's red light is NOT scattered as much as blue light by atmospheric particles and so solar blue light is scattered away from your eyes on its way from the sun and red light is scattered less. The result is that more solar red light hits your eyes than blue and sunsets appear red. Notice also that the redness of sunsets increases at the amount of atmospheric particles between you and the sun increase, that is as the sun "goes down" mie scattering increases as the amount of particles between you and the sun increases. [Webster's New World Dictionary; Third Edition: page 265; 1994.] [Scientific American; v265: pages 80-85; 1991.]

Mixing Height - the height in the atmosphere where pollution gets mixed and dispersed through the atmosphere. Factors controlling this phenomenon include solar radiation, wind speed, and local surface roughness. The mixing height is located at the top of a boundary layer and at the base of a temperature inversion. [Journal of Atmospheric Environment, Volume 36, Issue 22, August 2002, Pages 3699-3708] [Journal of Atmospheric Environment, Volume 34, Issue 7, 2000, Pages 1001-1027]

Mixing Ratio - The fixed proportions in which two or more substances may become combined, such as the amount of nitrogen in the air compared to the rest of the air. Atmospheric scientists routinely discuss the gas phase concentrations of trace components in mixing ratios expressed in ratios of VOLUMES, as in "the present tropospheric mixing ratio for methane is approximately 1.7 ppmv." [Science; v261: pages 1130-1134; 1993.] [Nature; v354: pages 382-284; 1991.]

MMT - (methylcyclopentadienyl manganese tricarbonyl, C9H7MnO3) an organometallic compound sold as a gasoline additive. It is added to gasoline--just as tetraethyl lead, the chemical it replaces, was--to enhance the gasoline's octane thereby increasing burning characteristics, lowering engine wear, and raising gas mileage. It was banned by the US Clean Air Act from 1977 to 1995. After 1995, up to 1/32 g Mn as MMT/gallon gasoline could be sold in gasoline in the US; however, U.S. gasoline formulators use of MMT is small. This organo-metallic compound has been found to be toxic to humans at the concentration experienced by workers in, for instance, an industrial setting where high concentrations are used (and spilled), but apparently not in airborne concentrations, such as car emissions where the final manganese forms are as the phosphate, sulfate, and oxide produced during internal combustion by the engine. Symptoms of acute MMT exposure range from skin and eye irritation to liver damage to neurological damage. [Neurotoxicology; v25; 433-441; 2004; DOI:10.1016/j.neuro.2003.10.001] [Science of the Total Environment; v366; 143-147; 2006; DOI:10.1016/j.scitotenv.2005.09.094] [Atmospheric Environment; v41; 7995-8006; 2007; DOI:10.1016/j.atmosenv.2007.08.002] [Atmospheric Environment; v45; 6459-6468; 2011; DOI:10.1016/j.atmosenv.2011.07.035]

Mobile Source - (also call non-point source) consist of emissions from on-road and off-road sources. Cars, light, medium and heavy-duty trucks are considered on-road mobile sources, off-road mobile sources; are tractors, lawn mowers, boats, and airplanes. Although the off road sources usually put out more pollution per hour of work than the on-road, the great number of on-road source put out a larger overall volume into the atmosphere. [Atmospheric Environment;v42; p6951-58;2008; DOI:10.1016/j.atmosenv.2008.04.057]

Molecular Oxygen - A molecule that is composed of two oxygen atoms, O2, and has no color, odor, or taste. It is present in both the atmosphere and dissolved in the oceans and freshwater sources exposed to the atmosphere. Solar radiation with wavelengths less then 242 nm can break it back into oxygen atoms,

O2 ---> O + O

One of these oxygen radicals in turn can combine with O2 to form ozone,

O2 + O ---> O3

This last reactions requires quick collision with a third body to remove the excess energy of the ozone product. [Science; v265: pages 1817-1818; 1994.] [Science; v235: pages 199-202; 1987.]

Monsoon - Heavy winds characterized by a pronounced seasonal change in direction. Winds usually blow from land to sea in the winter, while in the summer, the flow reverses and precipitation is more common. Monsoons are most typical in India and southern Asia. [Chemical Geology; v259; 168-80; 2009; DOI:10.1016/j.chemgeo.2008.11.001]

Montreal Protocol - A international environmental agreement (one of the first) to prevent the use of substances that are harmful to ozone, such as chlorofluorocarbons and halons, in order to protect the ozone layer in a global manner. It was agreed upon in 1987 and has been amended repeatedly since that time. [Science; v265: page 1806; 1994.] [Nature; v367: pages 505-508; 1994.]

MTBE - the compound methyl tertiary butyl ether (MTBE) was blended in gasoline originally in 1979 to serve as an oxygenate. This would theoretically cause the combustion process in internally combustion engines to be more complete. This effort to improve air quality by producing a fuel that was more readily oxidized and decrease the resulting tropospheric ozone production was somewhat effective. A problem arises, however, in the fact that MTBE moves extremely well in water (it may actually move upstream because of its high affinity for water molecules), causes fish kills due to its toxicity to fish, and even at low concentrations, it can render large surface or groundwater sources to be useless. Its use has since been banned in California. [Environmental Science and Technology A-Pages; 39(13); 279-279; 2005.] [Industrial and Engineering Chemical Research; 46; 2508-2519; 2007.] [ [Environmental Forensics; v2; 17-19; 2001; DOI:10.1006/enfo.2001.0028]


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Nacreous Clouds - Clouds that occur in the stratosphere at altitudes above 20 km and are usually iridescent and luminous in color. They may also be called mother of pearl clouds. [Science; v264: page 527; 1994.] [Webster's Third new International Dictionary; Third Edition: page 1499; 1986.]

Naphthalene - A naturally occurring volatile organic compound, it is a component of petroleum and coal and is released by the burning of wood or tobacco. It is also used in moth repellants, dyes and pharmaceuticals. Like other nonmethane hydrocarbons it is oxidized and subsequently it reacts with NO in the atmosphere to produce NO2. The NO2 is photolyzed to produce NO and O. The O then reacts with O2 to produce ozone. [Journal of Hazardous Materials; v164; 195-203; 2009; DOI:10.1016/j.jhazmat.2008.07.143]

National Ambient Air Quality Standards (NAAQS) - Sets the levels of air quality for the United States , in the Code of Federal Regulations (40 CFR 50.2), to protect the population's health. These are the minimum and might be more stringent from state to state. [Atmospheric Environment; v40; 5041-5055; 2006.]

National Center for Atmospheric Research (NCAR) - A non-profit organization dedicated to furthering understanding of the Earth's atmosphere. Located in Boulder, CO, U.S.A., NCAR is operated by the University Corporation for Atmospheric Research (UCAR) and sponsored by the National Science Foundation (NSF). [Atmospheric Environment; v40;p7508-27; 2006; DOI:10.1016/j.atmosenv.2006.07.016]

National Oceanic and Atmospheric Administration (NOAA) - A United States Government agency created in 1970 as part of the United States Department of Commerce to determine how our oceans and atmosphere should be developed, regulated, analyzed, formed, and mined. NOAA tries to achieve these goals with the help of eight major federal services, The National Oceanic Survey, The National Weather Service, The National Fisheries Service, The Environmental Research Laboratories, The Environmental Data Service, The Environmental Satellite Service, The Office of Sea Grant, and The Office of Coastal Zone Management. NOAA has been threatened with extinction in the spring of 1995 with the possible dissolution of the Department of Commerce under the guise of "necessary" budget cuts. [Encyclopedia America; v19: page 765; 1993.] [Audubon; v88: pages 36-39; 1986.]

Natural Gas - The product of the decomposition of fossilized carbon and organic matter in the crust of the earth. Generally, it is composed of mainly methane, and leaks are a source of methane in the atmosphere. It is also extensively mined, of course. [Energy; v32; 1163-1176, 2007.]

Near Infrared Radiation - A term that represents the shortest wavelengths in the infrared spectrum. They are from 0.78 µm to 2.5 µm. 0.78 µm is 780 nm, the edge of the visible spectrum. In the atmosphere, the amount of near IR reflectance correlates with crop biomass. [Remote Sensing of Environment; v115; 1464-1477; 2011; DOI: 10.1016/j.rse.2011.02.006; Remote Sensing of Environment; v115; 1694-1705; 2011; DOI: 10.1016/j.rse.2011.02.027]

Nimbostratus Clouds - Cloud formation consisting of dark-gray layers of clouds and occurring at altitudes which produce prolonged rain and snow. [Atmospheric Science; v50; 120-36; 1993.] [Atmospheric Science; v51; 711-28; 1994.]

Nimbus Clouds - Nimbus is a term used to describe a cloud that is precipitating. [Physics Today; v 47; pages 36-42; 1994.] [Journal of the Atmospheric Sciences; v 51; pages 3183-3193; 1994.]

Nitric Acid - HNO3, this is a corrosive, non-volatile, and inorganic acid. It is a strong acid (dissociates completely in aqueous solution) and is also an oxidizer. In the atmosphere it is formed by the conversion of nitrogen monoxide into nitrogen dioxide, and ultimately into nitric acid:

2NO + O2 --> 2NO2
3NO2 + H2O --> 2HNO3 + NO

Nitrogen monoxide in this process most often come from (fossil fuel-based) combustion processes that use atmospheric air (containing 78.1% N2) which combines with atmospheric oxygen in those high temperature combustion process (see nitrogen monoxide and nitrogen dioxide entries below). Nitric acid is highly water soluble. This solubility with water allows easy removal of nitric acid from the troposphere by atmospheric precipitation. Commonly, this is referred to as acid rain or snow. Nitric acid has a relatively low concentration in the atmosphere but provides an important role in the production of sulfuric acid. It acts as a catalyst in the conversion of sulfur dioxide to sulfuric acid. Sulfuric acid is usually formed within cloud droplets by oxidation of dissolved sulfur dioxide again most often released by fossil fuel combustion. [T.E Graedel and Paul J. Crutzen. Atmospheric Change: An Earth System Perspective. WH Freeman and Co, NY.1993.] [Journal of the Atmospheric Sciences; v47; 2696–2709; 1990.]

Nitric Oxide Radical - This radical is a primary pollutant from many sources, the most common and abundant is automobile exhaust. It's importance in the atmosphere is great because it is a catalyst in the destruction of ozone. [Journal of Applied Meteorology; v39; 275–290; 2000. ] [Journal of Geophysical Research, v107; 1-14; 2002.]

Nitrification - The conversion of nitrogen organic compounds to inorganic compounds of nitrogen. This conversion is accomplished, in the main, by bacteria. [Applied and Environmental Microbiology; v60; 3307-3314; 1994.] [Nature; v342; 895-897; 1989.]

Nitrogen - N2, a colorless, tasteless, odorless gas which makes up 78.1% of the atmosphere. Atmospheric nitrogen is converted by nitrogen fixation and nitrification into compounds used by plants and animals. In the far upper atmosphere, N2 is broken down when large numbers of energetic secondary electrons are produced and available to react with the N2. This leads to the eventual production of NO in that part of the atmosphere and is not--by definition--anthropogenic in nature. [Crutzen, Paul J. and T.E. Graedel, Atmospheric Change. W.H. Freeman and Company, New York, ; 1993; 147.] [Journal of the Atmospheric Sciences; v37; 179–192; 1980.]

Nitrogen Cycle - Nitrogen cycling is an extremely important natural process, in which nitrogen-containing species such as ammonia, nitrate, and nitrite, are absorbed into the soil, atmosphere or the ocean and are used by many living organisms to produce amino acids and proteins or other volatile gases. This movement of nitrogen between living organisms, soil, water, and atmosphere is a crucial part of crop production on earth. Interactive animation of the nitrogen cycle. [Environmental Pollution; v102; p15-24; 1998; DOI:10.1016/S0269-7491(98)80010-9]

Nitrogen Dioxide - NO2, is the lesser of the two emitted NOx gases from high temperature combustion in air; NO the other. NOx production occurs in all internal combustion engines that use atmospheric oxygen from the air as oxidant, a process that brings atmospheric N2 along with it. NO2 is a very important species in the atmosphere. Since it absorbs in the visible wavelength region--creating the Brown Cloud over Denver, LA, Mexico City, Beijing, etc.--and can be photolyzed and yield oxygen atoms that can react with molecular oxygen to create ozone, NO2 and the NO/NO2 ratio are important in tropospheric chemistry. See nitrogen monoxide. [Environmental Science and Technology; v26; 74-79; 1992; DOI:10.1021/es00025a005] [Science; v242; 555-558; 1988; DOI:10.1126/science.242.4878.555] [Atmospheric Environment; v45; 3025-3033; 2011; DOI:10.1016/j.atmosenv.2011.03.023]

Nitrogen Fixation - The bacteria assisted conversion of molecular nitrogen, N2, to ammonia. [Ecological Modeling; v202; 362-372; 2007.]

Nitrogen Monoxide (nitric oxide) - NO is the principal emitted NOx gas from high temperature combustion in air. This gas can acts as a catalyst in the reactions that cause the destruction or creation of ozone: At high concentrations, NO consumes O3 in urban environments but NO is also oxidized to NO2 by alkyl peroxy radicals and that NO2 can subsequently be photolyzed by sunlight to free atomic oxygen, which quickly produces ozone (see nitrogen dioxide). Reacting with ozone and tropospheric radicals, NO is inextricably linked with the polluted urban atmospheric production of NO2, ozone, and other secondary pollutants such as peroxyacetyl nitrate. [Science; v242; 555-558; 1988; DOI:10.1126/science.242.4878.555] [Atmospheric Environment; 2011; DOI:http://dx.doi.org/10.1016/j.atmosenv.2011.01.073]

Nitrogen Oxides - NOx (pronounced "nox") are produced from high temperature combustion in air. They are nitrogen monoxide and nitrogen dioxide (see above). Nitrogen monoxide is produced to varying degrees by all internal combustion engines that use atmospheric air as a source of oxygen. [Science News; v146; 260-262; 1994] [Science; v242;555-558;1988.]

Nitrous Oxide - N2O, this is a by-product of biological activity of a symbiotic bacteria living in leguminous plant roots. It is a principal greenhouse gas that absorbs in the infrared wavelength region and unfortunately falls in an IR "window" between IR absorbing features of water and carbon dioxide (a characteristic of all the "trace" greenhouse gases with significant radiative forcing). It is also laughing gas used in medicine as a gentle general anesthetic. It is not an oxide of nitrogen in the NOx "family." [Nature; v335; 528-529; 1988.] [Atmospheric sulfur and nitrogen oxides; George Hidy; p13; 1986;Academic press: New York.]

NMHCs - See nonmethane hydrocarbons.

Noctilucent Clouds - Relatively unusual wavy, thin, bluish-white clouds that form at altitudes of about 80 to 90 km. [Air: the nature of atmosphere and the climate; Michael Allaby; p73; 1992; Curtis Garrat Limited; New York.] [Cloud investigation by satellite; Richard Scorer; p621; 1986; Ellis Horwood Limited; England.]

Nocturnal Boundary Layer - The layer of gas that forms above the surface layer as the gases of the convective mixed layer become more dense and lose their buoyancy. The formation of this nocturnal boundary layer is what caused the temperature inversion of the surface layer during the night hours. [Atmospheric Environment; v40; 856-855; 2006.]

Nonmethane Hydrocarbons (NMHCs) - These are hydrocarbons such as ethylene, butane, hexane, propane and, by definition, exclude the first member of that analogous series, CH4. Large quantities of NMHCs are emitted from vegetation, the vast majority as isoprene, C5H8. The natural emission of isoprene is significant compared to that of anthropogenic NMHC. [Nature; v329; 705-707; 1987.] [Nature; v329; 705-707; 1987.]

NOx - See nitrogen monoxide, nitrogen dioxide, and nitrogen oxides.

Nuclear Winter - In the event of a significant nuclear war, researchers (Paul Crutzen and John Birks initially) predicted that a barrier of smoke (from incinerated urban centers and forests) would fill tropospheric skies--and punch oxides of nitrogen and bomb debris into the stratosphere. Tropospheric smoke would---depending on the extent of the exchange---eventually surround the earth, reducing the tropospheric temperature and causing damage to ecosystems and atmospheric components such as stratospheric ozone. Others have calculated the size of nuclear explosions that are required to get bomb debris into the stratosphere: at mid to high latitudes where the tropopause is lower only 30 kiloton weapons are required; the U.S. atomic bombs used during the Second World War averaged less than 18 kilotons. At low latitudes, where the tropopause is highest, >1 megaton weapons are required to loft bomb debris into the stratosphere. [Ambios, v11, pages 115-125, 1982.] [Science; v247; 166-176; 1990.] [Chemistry in Britain; pages 927-930; November 1983.]

Nucleation - A process in which water condenses on a small atmospheric particle. Nucleation aides in the process of condensation (see methanesulfonic acid). [Journal of Atmospheric Sciences; v51; 1843-1856; 1994.] [Nature; v365; 823-826; 1993.]

Nucleation Scavenging - Term for water vapor that removes particulate matter from the atmosphere. [Journal of Atmospheric Sciences; v49; 1264-1265; 1992.] [Journal of Applied Meteorology; v33; 775-784;1994.]

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