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Atmospheric Chemistry Glossary


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Haboob - Sandstorms that occur in the deserts. As a thunderstorm is ending there is a decrease in water droplet fall. The desert's air is extremely dry and able to evaporate the water as winds rush towards the desert's surface. As winds continue to hit the surface they form a circular wind pattern containing sand which increases in force and speed to form the sandstorm. In the summer of 2011 a haboob hit Phoenix Arizona USA that was 100 miles wide and a mile high. Sandstorms blowing west off Africa take phosphate out towards the Atlantic Ocean and sometimes even as far as South America. This phosphate may be an important source of phosphorus in phosphorus-limited biomes. [Williams, T.; New York Times, Jul. 6, 2011.][U. Brunner and R. Bachofen; Technological and Environmental Chemistry, v67; 171-188, 1998.] [Atmospheric Research; v61; 75-85; 2002; DOI:10.1016/S0169-8095(01)00092-8] [Aeolian Research; v2; 205-214; 2011; DOI:10.1016/j.aeolia.2010.11.001]

Hadley Circulation - proposed by George Hadley in 1735, it is the tropical convection system that describes the atmospheric thermal circulation of air from the equator (0 degrees latitude) poleward to 30 degrees both north and south of the equator. When saturated air at the intertropical convergence zone (ITCZ), located approximately at the equator, is heated, convergence and convection causes it to rise into the upper atmosphere, creating an area of low pressure at the earth's surface. As the pocket of saturated air at the ITCZ rises, it cools, releasing large amounts of precipitation. Rather than remaining in the tropics, the air then flows horizontally towards the higher latitudes. At approximately 30 degrees both north and south of the equator, the pocket of air in the upper atmosphere has sufficiently mixed and cooled enough to return to the surface. To complete the circle, the area of low pressure at the equator pulls air in from the higher latitudes. [Journal of Atmospheric Science, v52; 3945-3959; 1999; DOI:10.1175/1520-0469(1995)052<3945:ROMCOT>2.0.CO;2] [Atmospheric Research; v91; 500-507; 2009; DOI:10.1016/j.atmosres.2008.06.014]

Half-Life - The time that is required for a substance to reach fifty percent or one-half its initial mass. This can be radioactive decay or through chemical interaction. For instance, the half-life of carbon-14 is 5730 years; it decays to nitrogen-14. The atmospheric half life of hydroxyl radical (seconds) is not based on radioactive decay (it's radioactively stable) but on the chemical processes by which it is removed from the atmosphere. The half-life of atmospheric chemical species is often most strongly affected by reactions that have the fastest rate of reaction (see Reaction Rates). [Tetrahedron Letters; v37; 5939-5942; 2009; DOI:10.1016/0040-4039(96)01282-8] [Atmospheric Environment; v39; 2189-2200; 2005; DOI:10.1016/j.atmosenv.2005.01.007]

Halocline - In the oceans, a well-defined steep vertical gradient of salinity, a change in aquatic salinity with depth. Though this varies with latitude, the halocline is from about 70 to 200-300 meters below the surface. The Arctic halocline could be influenced by fresh water influx from Arctic rivers. A sudden change in the North Atlantic's halocline could, for instance, effect the long-range oceanic currents such as the Gulf Stream; this could, for instance, effect the climate of Northern Europe. [Deep Sea Research Part I: Oceanographic Research Papers; v52; p1988; 2005.] [Deep Sea Research Part A. Oceanographic Research Papers; v34; 1957-1979; 1987; DOI:10.1016/0198-0149(87)90093-8] [Applied Ocean Research; v33; 69-78; 2011; DOI:10.1016/j.apor.2010.10.004]

Hartley-Huggins Band of Ozone Absorption - This spectral band in the UV is responsible for the absorption and filtering of solar ultraviolet radiation. Photons with a wavelength longer than 210 nm are weakly absorbed by oxygen in the atmosphere. Ozone then becomes the major UV absorber, with a band of 210-380 nm. Compare to ozone's Chappuis band in the visible wavelength region. [Journal of Chemical Physics; v 101 p. 2968; 1994] [Journal of Chemical Physics; v 89; p 6667; 1988.]

Hazardous Air Pollutants (HAP's) - air pollutants, as defined by the U.S. Clean Air Act, that present a threat to human health and/or the environment. Pollutants include asbestos, beryllium, mercury, benzene, etc. The creation of various monitoring programs set up by the Environmental Protection Agency, allow for the regulation of the required 188 hazardous air pollutants. [Atmospheric Environment; v36; 1783-1791; 2002; DOI:10.1016/S1352-2310(02)00160-7] [Atmospheric Environment; v30; 3443-3456; 1996; DOI:/10.1016/1352-2310(95)00200-6]

Haze - An atmospheric aerosol of sufficient concentration to be visible. The particles are so small that they cannot be seen individually but are still effective in visual range restriction. The Blue Ridge Mountains of the Eastern United States have a haze caused by the natural emissions of hydrocarbons (mostly isoprene-see below) which are oxidized and form aerosols. [Graedel, T.D. and Paul Crutzen. Atmospheric Change: an Earth system perspective; 1993; Freeman Press.] [Atmospheric Environment; v41; 1267-1274; 2007: DOI:10.1016/j.atmosenv.2006.09.051]

HCFs - See hydrochlorofluorcarbons.

Heat Flux - The amount of heat that is transferred across a surface of unit area in a unit of time. [Physics and Chemistry of the Earth; v28; 75-88; 2003.] [Atmospheric Environment; v40; 2750-2766; 2006; DOI:10.1016/j.atmosenv.2005.11.061]

Henry's Law - The relationship that defines the partition of a soluble or partially soluble species between the gas and solution phases. It is often represented as Hc. It is the relationship of species dissolving but not reacting in solution to those in equilibrium in the gas phase. The equation used for this is: [Caq] = [Hc]*[Cg ]. Hc is the Henry's Law Constant. This may be regarded as a measure of the molecules in a gas to those dissolve in solution, and this relationship is temperature dependent. Cg and Caq are the concentrations or partial pressure of species C in gas and aqueous solution, respectively. [Environmental Science and Technology; v 28; p 2133; 1994] [Journal of the Tennessee Academy of Science; v 69; p 1; 1994.]

2-Hexanone - C6H12O, is a volatile organic compound (VOC) which are a large family of carbon-containing compounds which are emitted into the atmosphere from a variety of industrial processes. 2-hexanone may have the potential to contribute directly to global warming by absorbing infrared radiation from the earth's surface. In general the more complex a VOC, the greater its ability to absorb infrared radiation. 2-hexane may also contribute indirectly to global warming through the change in concentration of ozone, which is a potent greenhouse gas. [Toxicology Letters; v75; 51-58; 1995.][Toxicology and Applied Pharmacology; v79; 166–174; 1985; DOI:10.1016/0041-008X(85)90379-5]

Hexafluoroethane - C2F6, an odorless halocarbon that meets all requirements of a greenhouse gas: unreactive to OH… and ozone, does not photodissociate from either UV or visible light, is insoluble in water, and absorbs in the infrared spectrum. [Journal of Fluorine Chemistry; v16; 199-208; 1980.] [Journal of Fluorine Chemistry; v121; 193-199; 2003; DOI: 10.1016/S0022-1139(03)00015-0]

Horse Latitudes - This is the area between 30ƒ and 35ƒ latitude where the dense cool air descends and the winds become weak. According to some traditions sailors relying solely on wind power threw their horses overboard in hopes that speed would increase due to the resulting lighter load of the ship. Other traditions state that the horses were thrown overboard to avoid depleting their provisions and still another states that this is simply the region where the horses perished. [World Book Millennium 2000; v.9, p.363][Encyclopedia of Weather and Climate; v.1, p.277]

HPLC - High-performance liquid chromatography (HPLC) is used to determine the amount of a compound in various media such as the air, water or blood. Though there are many gas-phase atmospheric components that are most easily separated by gas chromatography, some of the urban air compounds are best analyzed using HPLC. Examples are the multi-ringed aromatic compounds created in urban environments and condensed on urban particulates. Samples of the desired media (air, water, etc.) are dissolved in solution and then separated by injecting the solution into mobile phase solution which is separated via interaction with a stationary phase. As the solution passes through the stationary phase, the components are separated based upon different partitioning behaviors between the components in the mobile phase and the stationary phase. This allows each component to be analyzed separately as they pass through the detector. [Journal of the Association for Laboratory Automation; v10; 381-393; 2005.]

Humic Matter - is part of humus, and is a mixture of amorphous, polydispersed colloidal, yellow to brown-black organic substances. They are hydrophilic, and high in molecular weights, which range from a few hundreds to thousands of daltons. They have originated from the decomposed, non-humic, organic fraction by "new formation," called humification. [Tan, Kim H. Humic matter in soil and the environment. Principles and controversies; 2003; Marcel Dekker.]

Humidity - The moisture content of air. Relative humidity is the ratio of the amount of water vapor actually present in the air to the greatest amount possible at that temperature (the saturation vapor pressure). [Solid State Ionics; v161; 267-277; 2003.]

Hydrazine - N2H4, also called diazen, is an unstable and extremely toxic chemical similar in structure and properties of ammonia. It is colorless and flammable and can be used as a propellant in liquid rocket fuels, granting more control and thrust than solid fuels.  Hydrazine is a strong candidate in the search for a zero emissions fuel for automobiles.  It produces more energy than fossil fuels in some reactions and still has water as a byproduct.  However, because it is so toxic and volatile, it cannot be deemed safe for the everyday driver's vehicle. The largest chemical loss of hydrazine in the atmosphere is due to reaction with the hydroxyl radical and with ozone.  The half-life of hydrazine because of these reactions vary from 3.7 hours (for the hydroxyl radical) to 13 hours (reaction with ozone). [International Journal of Mass Spectroscopy; v210-211; 503-509; 2001; DOI:10.1016/S1387-3806(01)00392-X]

Hydrocarbons - Chemicals containing only carbon and hydrogen. These are of prime economic importance because they encompass the constituents of the major fossil fuels, petroleum and natural gas, as well as anthropogenically produced plastics, waxes, and oils. In urban pollution, these components--along with NOx and sunlight--contribute to the formation of tropospheric ozone. [Nature; v372; 455-458; 1994.] [Journal of Economic Issues; v28; 755-775; 1994.]

Hydrochlorofluorocarbons - HCFCs, chemical species slated to replace CFCs in the near future in most Western nations. When the normal chlorofluorocarbons (see above) reach the stratosphere and are photo-decomposed, their released chlorine radicals destroy the natural ozone that acts as our umbrella to shield the Earth from ultraviolet radiation (see chlorine and ozone). With one or more hydrogen-carbon bonds, HCFCs are still useful as replacement for CFCs in most applications. However, this bonding structure makes HCFCs much more chemically unstable--as compared to CFCs--and therefore subject to hydroxyl radical and ozone attack early in their gas phase career in the atmosphere. In fact they react in the troposphere instead of the stratosphere. Their atmospheric lifetime is shorter than CFCs and they, therefore, have a smaller chance of reaching the stratosphere where their chlorine could be released by destructive photolysis and enter the catalytic ozone destruction cycle. [Spectator; v 272; p 9-11; 1994] [New Scientist; v 141; p 6-7; 1994.]

Hydrogen Bromide - HBr, In the stratosphere, ozone is continuously being formed via the Chapman mechanism. However, halogen radicals such as atomic bromine and atomic chlorine (released from anthropogenic and some natural sources) catalyze the breakdown of ozone which results in a net ozone loss:

O3 + Br ----> BrO + O2

A reservoir species is a compound whose formation breaks the destruction cycle by taking the halogen radical out of the cycle. Two examples are HCl and HBr. Unfortunately, the success of HBr as a reservoir species is very limited due to the fact that it, unlike HCl, photodissociates quickly and easily. Thus, the ozone depleting effects of bromine are, atom for atom, more severe than those of chlorine. [Graedel, T.D. and P. Crutzen. Atmospheric Change: an Earth system perspective; 1993; Freeman Press.] [Journal of the Atmospheric Sciences; 37; 339-353; 1980.] [Journal of the Atmospheric Sciences; 63; 1028-1041; 2006.]

Hydrogen Chloride - HCl, anhydrous hydrochloric acid. Its molecular weight is 36.47 g/mol; it is a colorless, corrosive gas. Hydrogen chloride is a covalent bonded nonflammable gas and ionizes almost completely when dissolved in water. When dissolved in water, hydrogen chloride forms a strong acid, hydrochloric acid. In the stratosphere, HCl acts as a reservoir species temporarily removing chlorine radicals from a catalytic ozone destruction cycle. (See ozone and chlorine.) [The journal of Physical Chemistry; v 98; p 2836; 1994] [New Scientist; v 137; p 19; 1993.]

Hydrofluoric acid - HF, A clear, corrosive liquid that has an extremely pungent odor and forms dense white vapor clouds if released. Both the liquid and the vapor can cause severe burns to all parts of the body, and medical treatment is required for all exposures. In fact, HF burns covering only 2% of the body can be fatal. If this chemical comes in contact with glass, concrete and other silicon-containing materials, it yields silicon tetrafluoride gas. In general, this chemical is used to produce environmentally safer fluorocarbon products, chemical derivatives, and fluoropolymers. Environmentally speaking, hydrofluoric acid is much too reactive to ever reach the upper atmosphere, and tropospheric sources therefore do not interfere with the ozone layer. Hydrogen fluoride, however, is produced in situ in the stratosphere by the photolytic destruction of anthropogenic CFCs. And while this process also frees atomic chlorine which catalytically destroys ozone, Cl can be sequestered as HCl, and temporarily removed from the O3 destruction cycle. Analogously HF also forms but unlike the chlorine reservoir species HCl which is eventually broken apart by hydroxyl radical, HF is too stable for th OH dot attack, and so the only significant stratospheric sink is eventual diffusion into the troposphere. [Chemical Week, v 164(45); 35; 2002.] [Chemical Market Reporter, v 262(12); 31; 2002.] [Atmospheric Environment; 15; 1579-1582; 1981.] [Journal of Geophysical Research; 2; 443-444; 1975.]

Hydrogen Peroxide - H2O2, this compounds molecular weight is 34.02g/mol; it is a colorless, rather unstable oxidant with a bitter taste and caustic to the skin. Hydrogen peroxide will decompose, liberating oxygen. Pure hydrogen peroxide is stable, but the slightest impurity will enhance decomposition, often violently. Concentrated solutions of hydrogen peroxide are highly corrosive and toxic. H2O2 is used as bleach, deodorizer, and in the manufacturing of rocket fuel. The hydrogen peroxide in your bathroom is approximately 3 percent in water. In the atmosphere this is one of the oxidizers for sulfur dioxide in cloud water droplets that produces sulfuric acid, a major component in acid rain. [Atmospheric Environment; v13; 123-137; 1979; DOI:10.1016/0004-6981(79)90251-8][Science; v 262; p 1883-1886; 1993] [Science; v 260; p 71-73; 1993.]

Hydrogen Sulfide - H2S, hydrogen sulfide is a reducing species, which is relatively unstable but survives for rather a long time owing to its slow reaction with atmospheric oxygen. This sulfur-containing gas is a major participant in gas to particle conversion in the atmosphere. Many sulfur-containing gases are reactive and thus are rapidly converted to sulfuric acid. [Analytical Science, 67(2); 318-323; 1995.]

Hydrologic Cycle - The recycling of water on earth. There are five steps: Condensation occurs when water vapor in the atmosphere turns into a liquid and forms clouds. The clouds release precipitation in the form of rain, snow, or sleet when the moisture in the clouds becomes too heavy. Infiltration occurs when the water seeps into the ground, The infiltration rate depends on the permeability of the ground. When there is too much water on the surface to infiltrate into the ground, it becomes runoff and ends up in lakes, streams, or oceans. Evapotranspiration is a two part process driven by the sun. Evaporation occurs when water is turned into a vapor from the ground and transpiration is water loss by plants, The water vapor rises and starts the process over again. [Environmental Science and Technology; v36n17; pages 3652-3661; 2002] [Nature; v419n6903; pages 224-233; 2002]

Hydrometeors - Any condensed form of water--larger than a single water molecule--that is falling or suspended in the atmosphere; some examples of hydrometeors are snow, fog, cloud or rain. When these particles reach the size of 10-20 micrometers, available water is depleted and a stable cloud is formed. [Journal of Geophysical Research. Atmospheres; v 96; p 20809; 1991.] [Nuclear Instruments and Methods in Physics Research; v 79; p 397; 1993.]

Hydroperoxy Radical - HO2, this radical readily reacts with nitrogen oxides and hydrocarbons in the atmosphere; in urban atmospheres, the major source of the hydroperoxy radical is formaldehyde photolysis. [Atmospheric Chemistry; Finlayson-Pitts and Pitts; 34; 1986; Wiley Publishers; New York] [Journal of Chromatography; v579; 25; 1992.]

Hydrosol - A dispersion of solid particles is a liquid system. [Water, Air, and Soil Pollution; v69; 405; 1993] [Journal of Colloid and Interface Science; v136; 552; 1990.]

Hydrosphere - That part of the atmosphere which contains water in the liquid, solid, or gaseous phase. [Water Resources; v19; 255; 1992] [Chemical and Petroleum Engineering; v29; 125; 1993.]

Hydrothermal Chemistry - Aqueous chemistry under high temperature conditions. In biospheric chemistry, this refers to water whose chemical composition has been altered by deep, hot rock and which tends to come to the surface at fault lines. This creates boiling springs and geysers. [Atmospheric Change v.3; 179; 1993]

Hydroxyl Radical - OH, a molecule with an unpaired electron consisting of one hydrogen atom and one oxygen atom. This radical readily reacts with methane and other hydrocarbons in the atmosphere and can begin the process by which tropospheric oxygen is incorporated in a mechanism for the oxidation of NO to NO2. Photolysis of NO2 yields atomic O and quickly ozone at tropospheric pressures. In urban environments this is a major source of ozone:

OH + CH3CH3 ----> CH3CH2. + H2O

O2 + CH3CH2. ----> CH3CH2O2.

NO + CH3CH2O2. ----> CH3CH2O. + NO2

NO2 + hv ----> NO + O

O2 + O + M ----> O3 + M

The source of the hydroxyl radical in the atmosphere occurs primarily through the 1) photolysis of hydrogen peroxide, heat, and light and 2) the attack on water of an excited oxygen radical (created by the photolysis of ozone). [JAPCA; v39; 704; 1989] [Journal of Chemical Society; v85; 577; 1989.]

Hygroscopic - Having the characteristic of drawing moisture from the atmosphere. [Atmospheric Environment; v39; 4969-4982; 2005.]

Hypsometric Diagram - A graph that shows in any way the relative amounts of Earth's surface at different elevations with regard to sea level. [Geomorphology; v8; 263-277; 1993.]

Hypsometry - Hypsometry is a technique of mapping the elevation contour of both land and the ocean floor using tinting to illustrate a change in contour. [Chemical Reviews; v107; 467-485; 2007.]


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Ice Core - Often used by humans to determine the historic chemical composition of the atmosphere; the source of the ice core is the snow which falls on the glacier which consolidates upon freezing and in which gas bubbles are trapped upon freezing. These data can be used to determine the atmospheric concentrations of a number of constituents at that time, for instance the important greenhouse gases. 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. [Die Naturwissenschaften; v81; 502; 1994] [Science; v266; 1885; 1994. DOI: 10.1126/science.1141038]

Icelandic Low (IL) - An area containing a low atmospheric pressure system which remains between Greenland and Iceland. IL behavior is directly affected by the North Atlantic Oscillation (NAO). A positive NAO means that there is more pressure on the IL. This increase in pressure of the IL causes a greater amount of cold winds to be compressed in the area; this area is colder than usual and those areas farthest from it are warmer than usual. On the other hand, a negative NAO means that there is less pressure on the IL. Pressure decrease of the IL allows the cold winds to spread further south. [Science; v241; 1043-1052.] [Marine Geology; v210; 247-259; 2004.]

Ice Sheet - A thick glacier formed above land that covers an area close to 20,000 square miles. The only two ice sheets know today are Antarctica and Greenland with Antarctica being the biggest. [Quaternary Science Reviews; v28; p621-638; 2009; DOI:10.1016/j.physletb.2003.10.071]

Indoor Air Quality - A measure of the value or comfort of people with the air they breathe inside buildings and homes. "Suitable" indoor air quality can conferred on air in which there are no known contaminants at harmful levels as determined by appropriate authorities or--more likely--air with which 80% or more of the people exposed do not express dissatisfaction. [Microchemical Journal; v73; 221-236; 2002.]

Infrared Radiation (IR) - Energy that is emitted in the form of electromagnetic waves at a wavelength greater than about 750 up to approximately 30,000 nanometers. Although the earth absorbs almost all the IR, UV, and visible radiation the hits it, the surface of the earth emits only the longest wavelength radiation of these three, IR, in any significant amounts. It is this re-emission of IR towards space--and its subsequent absorbance, re-emission and scattering--that contributes to the process that heats the atmosphere. This re-emission and subsequent heating is a part of the greenhouse effect. [Solid State Communications; v88; 939; 1993] [Journal of Geophysical Research; v97; 11,513, 1992.]

Insolation - The solar radiation incident on a unit horizontal surface at the top of the atmosphere. It is sometimes referred to as solar irradiance. The latitudinal variation of insolation supplies the energy for the general circulation of the atmosphere. Insolation depends on the angle of incidence of the solar beam and on the solar constant. [Earth and Planetary Science Letters; v221; 1-14; 2004.]

Intergovernmental Panel on Climate Change (IPCC) - A group set up by the World Meteorological Organization and the United Nations Environmental Program in 1988, it consists of hundreds of scientists around the world who are studying the earth's atmosphere and climate change. Reports are released periodically beginning in 1990. [Energy Policy; v36; 3492-3504; 2008; DOI:10.1016/j.enpol.2008.05.023] [Atmospheric Environment, v42; 4665-4681; 2008; DOI:10.1016/j.atmosenv.2008.01.049]

Intertropical Convergence Zone (ITCZ) - The location in the atmosphere along both sides of the equator at which the strong upward motion of air (Hadley cell) is characterized by heavy precipitation in convective thunderstorms and by relatively low surface pressure. It is also called the equatorial low pressure belt. [Crutzen, Paul J. and T.E. Graedel. Atmospheric Change; Freeman Press, New York; 1993; p.57].

Inversion - An anomaly in the normal positive atmospheric lapse rate (change of temperature with increasing altitude). This usually refers to a thermal inversion, in which temperature of the atmosphere increases rather than decreases with height. [Journal of Atmospheric and Solar-Terrestrial Physics; v68; 1752-1763; 2006.]

IR - See infrared light.

Iridescent Clouds - Clouds that appear in a swirl of various colors. As a cloud of this nature forms it is composed of small droplets which are almost entirely uniformly spread; however this may change as the cloud grows. When the sunlight interacts with these droplets, and at a greater angle from the sun (for instance, sunrise or sunset but with the sun often hidden behind other clouds), solar radiation is scattered by the small droplets. This scattering occurs for different wavelengths approximately equally. That is why these thin clouds appear in a swirl of rainbow colors. [Journal of the Franklin Institute; v197(1); p.56; 1924; DOI:10.1016/S0016-0032(24)90492-3]

Irradiance - The total radiant flux received on a unit area of a given real or imaginary surface. Also called the radiant flux density. [Advances in Space Research; v35; 882-890; 2005; DOI:10.1016/j.asr.2004.10.011][Advances in Space Research; v35; 376–383; 2005; DOI:10.1016/j.asr.2004.12.077]

Isentropic Lift - The rising of air as it moves through the atmosphere based upon density differences. Cold air is denser than warn air. The air which has a lower density will float or be lifted over the air which is more dense while moving toward air of the same density. That is why hot air rises by following an upward-sloping movement through the atmosphere while cool air sinks. [International Journal of Heat and Mass Transfer; v51; 2090-2106; 2009. DOI:10.1016/j.ijheatmasstransfer.2007.11.032]

Isobaric - Constant pressure along a surface. Imagine a column of air from the Earth's surface to the top of the atmosphere. Each point along the atmosphere's altitude containing the same pressure is an isobaric layer, a layer of the atmosphere's gases at constant pressure. [Fluid Phase Equilibria; v278; 62-67; 2009; DOI:10.1016/j.physletb.2003.10.071]

Isoprene - C5H5, a colorless volatile liquid which is insoluble in water, soluble in alcohol, and very reactive because of its low vapor pressure and double bonds. From an atmospheric chemistry point of view, isoprene is emitted from trees and plants, globally on the order of teragrams (500 x 1012 g) per year. This reactive, natural hydrocarbon may influence the oxidative/reductive balance in the biosphere where its concentrations are significant, in regions such as rainforests and large temporal forests. Most isoprene is directly emitted into the atmosphere from plant surfaces and some no doubt condenses on particulate matter. Emission rates from trees are positively correlated with leaf temperature and therefore, to a degree, time of day. Ultimately the carbon in isoprene is oxidized to carbon monoxide and finally carbon dioxide. [Oecologia; v99; 260; 1994] [Clinical Chemistry; v40; 1485; 1994.] [Journal Geophysical Research; v106(D20); 24347-24358; 2001; DOI:10.1029/2000JD900735]

Isopropylbenzene (Cumene) - C9H12, A colorless liquid with a gasoline odor, that is produced by petroleum refining, and combustion of petroleum products. It is a primary skin and eye irritant. Isopropylbenzene is used in paint thinner, additives to high octane aviation fuel, and the production of acetone. In the atmosphere it reacts with photochemically generated hydroxyl radicals. Its half life in the atmosphere is approximately 49 hours. [Chemical Research in Chinese Universities; v22; 371-374; 2006.]

1-Isopropyl-4-Methylbenzene - Commonly called P-cymene, a component formed by the oxidation of naturally produced terpenes, such as alpha-pinene, released by various trees such as the California Black Sage as well as Eucalyptus foliage. Anthropogenic emissions of this compound are from the production of p-cresol and other organic solvent compounds as well as its use in the flavor and fragrance industries. Exposure to this compound for the general public is usually from oral consumption of vapor inhalation from food sources that contain it as a natural component. [U.S. Coast Guard, Department of Transportation. CHRIS - Hazardous Chemical Data. Volume II. Washington, D.C.: U.S. Government Printing Office, 1984-5.][Environmental Science Technology v45; 2755-2760; 2011; DOI:10.1021/es103632b]

Isotopes - Two or more forms of an element that have the same atomic number but different numbers of neutrons in the atomic nucleus and therefore a different atomic weight. Most elements occur naturally as mixtures of isotopes. The symbol for an isotope usually consist of the mass number placed as a leading superscript before the elemental symbol. In atmospheric chemistry, long lived isotopes such as carbon-14 (14C) are used to determine the age of objects that contained living matter. Other isotopes are used to track the routes of air parcels in the atmosphere. [Science; v266; 1584-1586; 1994.] [Dictionary of Science; R.K. Barnhart; page 337; 1986; Houghton Mifflin Company; Boston.]

Jet Streak - Portion of the jet stream at which the winds reach a maximum velocity of 160 knots or more, the maximum winds within a jet stream. [Monthly Weather Review; v132; 297-319; 2004; DOI: 10.1175/1520-0493(2004)132<0297:ADSOJS>2.0.CO;2]

Jet Stream - The major atmospheric air currents centers over the Pacific and Atlantic Oceans, North America and over the Middle East. These systems are fairly robust from period to period, and across different observational data sets. The most important jet stream from our perspective at Sam Houston State University, in Huntsville Texas, USA , is the Pacific Jet, which helps set the storm tracks over the west coast of North America--like most northern hemispheric weather--moving towards the east. [Industrial and Engineering Chemical Research; v30; 1646-1651; 1991.]

Joule (J) - Defined as a SI unit which expresses a unit of energy. 1 J = 1 kg*m2/s2.[General Chemistry Third Edition; Wrighton, Mark S.; Ebbing, Darrell D; pp. 188-220; 1990; Houghton Mifflin Company: Boston.]

Junge Layer - Also known as the stratospheric aerosol layer, this is the lower layer of the stratosphere consisting of predominantly sulfuric acid/water particles with an average diameter of 0.14 μm, discovered in 1960 by Christian Junge while examining other atmospheric components. The sulfur in this layer probably comes from a stable biogenic gas released from the earth's surface, carbonyl sulfide, O=C=S, which is photolyzed and oxidized in the stratosphere. This is a more important sulfur source for the Junge Layer than reactive sulfur gases originating from the planet's surface because their lifetimes are too short to allow transportation beyond the tropopause [Science; v 299; 1566 – 1568; 2003; DOI: 10.1126/science.1079297] [Chemical Geology; v263; 131-142; 2009; DOI: 10.1016/j.chemgeo.2008.08.020]

Katabatic Winds - Strong winds associated with mountains and valleys. They occur when cold, dense air is produced by radiational cooling flows downhill due to the pull of gravity to a lower, warmer region such as depressions and valleys. [Barry, Roger G. and Richard J. Chorley. Atmosphere, Weather and Climate, 4th Edition, New York, NY., 1982.][Ocean Modelling; v35; 146–160; 2010; DOI:10.1016/j.ocemod.2010.07.001]

Katafront - A meteorological term used to describe a cold front where the warm winds force the cold air down at such an angle that there is no mixing and little precipitation is formed. These are often referred to as dry fronts. [International Geophysics; v13; 168 – 194; 1969; DOI:10.1016/S0074-6142(08)62799-0] [Atmospheric Research; DOI: 10.1016/j.atmosres.2010.11.002]

Keeling Fraction - Percentage of fossil fuel CO2 emissions that remain in the atmosphere, about 55%. Carbon dioxide mixing ratio measurements have been taken in Hawaii since 1958 by the research group of Charles David Keeling (1928-2005), a project initiated with support from Roger Revelle at Scripps Oceanographic Institute and Harry Wexler at the U.S. Weather Service. These data demonstrated that atmospheric carbon dioxide gas concentrations were increasing in the atmosphere and not just being absorbed by the ocean and plants. Atmospheric carbon dioxide gas phase concentration is lower during the spring when plants take up carbon dioxide and higher in the winter when the majority of plants are conserving energy, growing slower, and fallen plants are decaying and thus causing a rising fluctuation of carbon dioxide. [Atmospheric CO2 and 13CO2 exchange with the terrestrial biosphere and oceans from 1978 to 2000: observations and carbon cycle implications, pages 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.] [Science; v307; 1869; 2005.]

Kelvin Scale - Scale for measuring temperature that sets zero degrees at the point of which molecular motion desists, that is, the point at which there is no heat. It is also known as the absolute scale. [Weisberg, Joseph S. Meteorology, The Earth and Its Weather. New Jersey, 1976.]

Kinematic Viscosity - The ratio of absolute viscosity--or a fluid's resistance to flow--to the density of that fluid; this is commonly measured by determining the time it takes a liquid to travel through a capillary under the influence of gravity, using an instrument called a capillary viscometer, and can be expressed in units of m2 per s. The atmosphere's kinematic viscosity changes with altitude and this affects the rates at which gases exchange between layers. In general, the atmosphere's viscosity is higher at higher altitudes. [Fuel; v84; 1059-1065; 2005; DOI:10.1016/j.fuel.2005.01.016] [Building and Environment; v46; 1785-1796; 2011; DOI: 10.1016/j.buildenv.2011.02.007]

Kinetics - The study of the rates at which chemical reactions occur and the influence of physical and chemical conditions of these rates. [Electrochimica Acta; v52; 2294-2301; 2007.]

Knudsen number - is a unitless number describing the mean free path length of a particle relative to some characteristic length, often the diameter of the particle. The application of this measurement is applied to the determination of gas behavior to define the extent to which the gas behaves as independent particles. [International Journal of Heat and Mass Transfer; v36; 2941-2946; 1993; DOI:10.1016/0017-9310(93)90112-J]

Krakatua Winds - The winds produced as a result of the Krakatoa eruption on the island of Krakatua in 1883. This volcanic blast is the largest in recent times whose effects caused several atmospheric changes such as lowering the global temperature by 1.2 degrees Celsius and changing tides and wind conditions and providing beautiful red sunsets as far away as the United States . [Global and Planetary Change; v60; 576-588; 2008; DOI:10.1016/j.gloplacha.2007.08.002]

Konimeter - Defined as an instrument utilized to determine the amount of dust particles in a sample of air. [Journal of Aerosol Science; v29; 129-139; 2009; DOI:10.1016/j.physletb.2003.10.071]

Kyoto Protocol - An international agreement arranged in 1997 in an 11 day conference that took place in Kyoto, Japan. The agreement, coming into force in 2005, required industrialized countries to reduce greenhouse gas emissions, such as carbon dioxide, methane, nitrous oxide, hydrofluorocarbons (HFCs), perflurocarbons (PFCs), and sulfur hexafluoride, by an average of 5% (of 1990 emission levels) by 2008 – 2012. It was ratified by 141 countries including China and India but excluding the U.S., Australia, and Monaco. While some countries are on target to meet their emission cuts, many signatories will not meet their targets by 2012. [Science; v 296; 1971-1972; 2002; DOI: 10.1126/science.1071238] [Proceedings National Academy Sciences; v107; 1011-1016; 2010; DOI: 10.1073/pnas.0903797106]

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