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Atmospheric Chemistry Glossary

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Obliquity - The axis of Earth's rotation tilted all year perpendicular to the plane of the Earth's orbit around the sun. The angle is 23.5°. Because of this angle on December 22 the northern hemisphere has its winter solstice and the southern hemisphere has its summer solstice, and the latitude 23.5°S is the farthest point south at which directs sunlight hits. On June 22 the northern hemisphere has its summer solstice and the southern hemisphere has its winter solstice, and the latitude 23.5°N is the farthest point north that hit be direct sunlight hits. An animation illustrates this. [Journal of Physical Chemistry A; v98; 3037-75; 1994.], [Environmental Science and Technology; v33; 160A-63A; 1999.]

Ocean - The oceans cover approximately 70% of the Earth's surface and are apparently unique in the solar system (although keep an eye on some of the giant planets' moons...). The oceans are important for the regulation of tropospheric heat and the storage and production of oxygen and carbon dioxide. [Journal of Geology; v101; 191-213; 1993.] [Geotimes; v39; 12-15; 1994.]

Ocular Melanoma - A squamous-cell carcinoma that affects the cornea, iris, and related tissue of the eye. The cornea is the eye tissue that is most susceptible to UV-B damage. Individuals that spend their time at beaches, working outside, or skiing at high altitudes are most prone to UV-B damage. Welders who don't protect their eyes can also suffer this fate. Some other side effects of UV-B damage are snow-blindness and inflammation of the eye-ball. [Biochemistry; v34; 11175-86; 2004.] [Bioconjugate Chemistry; v14 ; 1177-85; 2005.] [American Journal Roentgenology; v191; 285-289; 2008; DOI:10.2214/AJR.07.2467]

Oleic Acid - When released into the air from cooking, can react with other atmospheric compounds, such as ozone, and create byproducts that are hazardous to our health. Oleic acid is a fatty acid found in animal and vegetable oils. It is called a mono-unsaturated fatty acid because of the single double bond between the carbons. It's physical properties are determined by the number, geometry, and position of this double bond and the degree of unsaturation. [Journal of Agricultural and Food Chemistry; v50; 1298-1305; 2002.] [Industrial and Engineering Chemistry Research; v36; 1485-90; 1997.]

One Dimensional AtmosphericModel - An atmospheric modeling technique in which a concentration or another unknown can be calculated relative to certain parameters, such as altitude or temperature. [Nature; v332; 667;1988.] [Journal of Atmospheric Sciences; v50; 3663-3676; 1993.]

Opacity - A measure of light blocking by atmospheric particles. [Environmental Science and Technology; v37; 630-7; 2003.] [Environmental Science and Technology; v127; 2120-27; 2004.]

Organic Matter - A combination of carbon, hydrogen, sulfur, oxygen, nitrogen, and other trace elements synthesized or originating from natural sources such as plants and animals. Human excreta, paper products, food, agriculture and much industrial wastes are all examples of organic compounds. The degradation of organic matter by organisms in soil release gases such as H2S, NH3, CH4 and CO2 the last two both important greenhouse gases because of their long atmospheric lifetimes and IR absorption characteristics. [Environmental Pollution; 110-120; 2006; DOI:10.1016/B0-12-370879-6/00133-2]

Outgassing- The release of "young" gases into the earth's atmosphere by volcanic activity. [Science; v259; 920-926; 1993.] [Nature; v409; 1083-1091; 2001.]

Oxidants - Chemical species that readily accept electrons. The electron accepting species is reduced in a chemical reaction. [Environmental Science and Technology; v28; 492; 1994.] [Chemical and Engineering News; v69; 30-43; 1991.]

Oxidation - A process that results in a species having a higher (more positive) oxidation state, that is, the net loss of electrons from an atom. Quite often oxygen is involved in the oxidation of another atom; therefore it is an oxidant. [Energy and Fuels; v14; p138-41; 2000.], [Industrial and Engineering Chemistry Research; v39; p4697-4701; 2000.]

Oxides of Nitrogen - See nitrogen monoxide, nitrogen dioxide, and nitrogen oxides.

Oxygen - O2, is found on Earth as a gas and constitutes about 20.8% of the air we breathe. Elemental molecular oxygen consists of two oxygen atoms bonded together. A photochemical reaction of oxygen is (ultimately) responsible for the production of ozone in the stratosphere. Oxygen concentrations found in ice core samples (using isotopic 16O/18O rations) have been used to determine past atmospheric levels of oxygen and have helped in determining past climates. [Nature; v351; 217-219; 1991.] [Nature; v365; 143-147; 1993.]

Oxygen Radical - O. is the result of the oxygen molecule (O2) being photodissociated at a wavelength less than 242 nm. These two oxygen atoms react with O2 (in the presence of a third body) and create ozone (O3). [Journal of Physical Chemistry A; v105; 7579 - 7587; 2001.] [Journal of Physical Chemistry A; v103; 5023 - 5031; 1999.]

Ozone - O3, is a molecule that consists of three oxygen atoms bonded together. The ozone layer in the stratosphere absorbs UV radiation and creates a warm layer of air in the stratosphere and is therefore responsible for the thermal structure of the stratosphere. Ozone that is present in the troposphere is mostly a result of anthropogenic pollution and therefore higher concentrations are found in urban areas. Ozone is involved with NOx in the photochemical production of many of the constituents of pollution environments (see nitrogen oxides and hydroxyl radicals.) [Chemical and Engineering News; v72; 6-7; 1994.] [Aviation Week and Space Technology; v140; 20-21; 1994.]

Ozone Depletion Potential (ODP) - The is the ratio of a particular ozone depleting compound environmental effect compared to the depleting ability of a standard compound, CFC-11, which is arbitrarily defined as 1.0. An example would be the ODP of of halon-1301 which is about 13. [The Journal of Chemical and Engineering Data; v46; 1031-34; 2001.], [Environmental Science and Technology; v31; 327-36; 1997.] [Nature; v398; 663-664; 1999.]

Ozone Destruction - In addition to photolytic destruction by infrared light (wavelengths of 1140 nanometers or less), stratospheric ozone is destroyed by interaction with a variety of chemical substances in the stratosphere. Some of these chemicals, such as the chlorine free radical--liberated by the photolysis of chlorofluorocarbons, are not normally produced there in nature at such high concentrations. This leads to the conclusion that human activities, and not natural chemical cycles, are responsible for the current rate of stratospheric ozone destruction. Ozone destruction is most noticeable (alarmingly!) over the South Pole, where seasonal plummeting in stratospheric ozone concentrations have been measured since the 1970s and are apparently still increasing (1999). That said, estimates based on declining CFC use (because of the Montreal Protocol) suggest that the damage to the global ozone layer will max out soon in the 21st century and that that ozone damage will decrease within the next 75 to 100 years. [Nature; v.370; p.429; 1994.] [Journal of Physical Chemistry A; v105; 1579-82; 2001.] [Science; v311; 12; 2006.]

Ozone Distribution- Nearly all of the planet's natural ozone in the atmosphere is found in the stratosphere. The thickness and distribution of this stratospheric ozone vary seasonally and by location. Ozone also occurs in the troposphere as a pollutant, often in photochemical smog. [Journal of the Atmospheric Sciences; v.50; 1033; 1993.] [Environmental Science and Technology; v34; 2324-29; 2000.]

Ozone Formation - Molecular oxygen in the stratosphere is broken into a pair of oxygen radicals by light with a wavelength of 240 nanometers or less. If one of these O radicals encounters an oxygen molecule, it can bond to produce ozone. This reaction is only stable if another molecule is present to absorb the excess energy released as the oxygen radical and molecule bond. This is a called a three body reaction, and the third body exhibits its removal of the excess energy by whizzing off at a higher energy and thereby increasing the temperature of the atmosphere where this reaction occurs. [Environmental Science and Technology; v.25; p.1884; 1991.] [Science; 292; 719-723; 2001.] [Nature; v443; 683-686; 2006.]

Ozone Hole - The ozone hole refers to the total amount of ozone in the atmosphere over Antarctica that was discovered to be decreasing at an alarming rate. The hole was discovered over an observation site in Antarctica by J.C. Farman, B.G. Gardiner and J.D. Shanklin. There is extensive evidence showing that chlorine originating from a class of synthetic compounds, the chlorofluorocarbons (CFCs), is responsible for the destruction of the ozone layer. CFCs are molecules that contain one or more atoms of both chlorine and fluorine. In September of 2006, the ozone hole over Antarctica was the largest area ever recorded and was almost THREE times larger than the area of the U.S. Because CFCs are so unreactive, they do not break down when released into the air in the troposphere where they are spilled. In time, air currents and diffusion carry them into the stratosphere, where, under the influence of UV radiation, they release chlorine radicals that initiate the destruction of ozone. Data collected by NASA have shown, conclusively, that there is an inverse relationship between ozone concentration and the chlorine monoxide radical in the stratosphere; ClO is formed by chlorine atom attack on O3. CFCs are very useful inert, nontoxic, nonflammable compounds that had been used for years as coolants and as spray can propellants for aerosol forms of hair sprays and deodorants. They had been unsurpassed as solvents for cleaning electronic microcircuits. Commercially, the most important CFCs are the halogenated methanes, Freon-11 (trichlorofluoromethane) and Freon-12 (dichlorodifluoromethane). Over 50% of asthma inhalers contain chlorofluorocarbons as the solvent and gaseous propellent. These CFCs have relatively recently been prohibited in all products except in those medicinal inhaler dispensers for asthmatics and a few other limited exceptions. In Finland alone there are over a million medicinal dispensers that disperse freons into the atmosphere. This is equal to the freon concentration of the cooling devices in approximately l00,000 refrigerators. [Buell and Girard, Chemistry, Prentice-Hall, Inc., l994.] [Journal of Physical Chemistry A; v101; 7350-58; 1997.] See Antarctic Ozone Hole for much more.

 

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Pangea - A huge protocontinent thought to have existed 200 million years ago and from which all present continents are thought to have formed. [Langmuir; v21; 2811-21; 2005.], [Journal of Physical Chemistry B; v107; 10063-76; 2003.]

Parent Elements - The element that underwent radioactive decay to produce a radioactive isotope and eventually produce a more stable product. This decay can be by the emission of an alpha particle, two protons and two neutrons, or by the emission of a beta particle, emission of an electron which changes a neutron to a proton. This is used in the dating of objects because the decay happens in a predictable known pattern. [L. T. Aldrich. Measurement of Radioactive Ages of Rocks. Science, v123; 871-875; 1956.] [Analytical Chemistry; v69; 1692-99; 1997.]

Parts Per Million (ppm) and Parts Per Billion (ppb) - These terms give scientists a way to describe how much of a substance is contained in a sample: parts of analyte per million parts of sample, for instance. In atmospheric chemistry these become volume parts of analyte per volume parts of atmosphere: ppmv, ppbv, etc. At low analyte gas phase concentrations the analyte is assumed to act as an ideal gas. For instance, a 1 ppmv concentration of formaldehyde would represent 1 liter of formaldehyde per every 1,000,000 liters of air; also equivalent to 1 microliter of H2CO per 1 L air. In gas phase concentrations these units are also called gas phase mixing ratios. The reason is because they are just that, ratios of analyte volume to sample volume; the volume of the sample doesn't matter. [Ecology A to Z; P. Fleisher; 150-161; 1994; Dillon Press; New York] [Occupational Environment; S. DiNardi; 1320; 1997; AIHA Press; Fair Fax, Virginia]

(Particulate Matter) PM2.5 - Aerosol particles that are smaller than or equal to 2.5 micrometers or have an aerodynamic diameter of 2.5 micrometers. In the Clean Air Act Revision of 1997 modified particulate standard to include PM2.5. Considered fine particle matter, PM2.5 has a greater effect of visibility and health than do larger aerosol particles, such as decreased lung function and premature death. [Journal of the Air & Waste Management Association; v55; 265; 2005.] [Science; v307; 1454; 2005.]

PCBs - See polychlorinated biphenyls.

PCV Systems - A PCV system is an air pollution control device in automobile engines. PCV stands for positive crankcase ventilation. Automobile makers began installing PCV systems in all new cars in 1963. It helps to recycle hydrocarbon contaminated gases inside the engine (blowby) back into the engine's combustion process. [Ecology A to Z; P. Fleisher; 150-161; 1994; Dillon Press; New York] [Occupational Environment; S. DiNardi; 1320; 1997; AIHA Press; Fair Fax, Virginia]

Pedosphere - This is the area of the Earth comprised of the solid plates of the continental crust, loose rocks and soil. [Water, Air, and Soil Pollution; v.70; 431; 1993.] [South African Journal of Science; v.86; 403; 1990.]

Pentanal - C5H10O is a flammable, volatile, colorless liquid. When this compound evaporates from industrial settings or, more commonly, is produced by tropospheric reactions in urban settings, it can contribute to the creation of ozone. [Journal Photochemistry Photobiology A: v143; 169-179; 2001; DOI:10.1016/S1010-6030(01)00524-X] [Atmospheric Environment. Part A. General Topics; v24; 1-41; 1990; DOI:10.1016/0960-1686(90)90438-S]

Penumbra - Partial blockage of light, for instance, part of a sunspot. In a large magnetic solar storm, the penumbra is the outer most ring of the storm composed of dark fibrils. During a solar eclipse--with the moon blocking the sun's light--the observers in the penumbra experience a partial blockage of the sun's light. [Analytical Chemistry; v67; 3453-59; 1995.] [Journal of Physical Chemistry B; v108; 3407-3409; 2004.]

Perfluoroethane -C2F6, see hexafluoroethane. [Journal of Physical Chemistry B; v105; 12126-33; 2001.], [Environmental Science and Technology; v37l; 4358-61; 2003.]

Perfluorooctane sulfonate (PFOS) - (CF3CF2CF2CF2CF2CF2CF2CF2SO3-) An intermediate in the production of fabric protectors that repelled water and oil, among other uses. PFOS is toxic to mammals. In 2005, Dupont decided to phase-out an analogue to this compound, perfluorooctanoic acid, by 2015 because of its widespread detection in blood of marine and Arctic animals. The 3M company is phasing-out perfluorooctane sulfonate for similar reasons. Recent data have shown that blood donors in Minneapolis-St. Paul, Minnesota have a lower blood concentration of members of this family after a 2000-2002 phase-out of perfluorooctanesulfonyl-fluoride. [Aquatic Toxicology; v82; 135-143; 2007.] [Chemosphere; v68; 105-111; 2007.]

Permafrost - Soil, silt and rock located in perpetually cold areas which remains frozen year-round. Though a thin layer may thaw during summer months, the majority of the permafrost in a given location will remain frozen until the local climate dramatically changes, as from continental drift toward the equator or global warming. [Geological Society of America Bulletin; v.100; 948; 1988.] [Science; v.234; 689; 1986.]

Peroxyacetylnitrate (PANs) - A class of chemical substances found as a pollutant in the troposphere, formed by photolysis from natural and manufactured organic chemicals. These chemicals act as irritants and mutagens in mammals and are toxic to many plants. [Atmospheric Environment; v.22; 973; 1988.] [Air and Waste; v.43; 1221; 1993

Personal Cloud - A relatively high measurement of pollution surrounding or near an individual organism that arises when the individual's movements stir up gases and particles on their clothes or nearby surfaces. The concentrations of personal clouds can range from 3-67 microgram/m3 for PM10, or 6-27 microgram/m3 for PM2.5. [Environmental Science and Technology; v33; 3645-52; 1999.] [Environmental Science and Technology; v34; 64A-65A; 2000.]

pH - The negative logarithm of the hydrogen ion concentration of a solution. It is the quantitative expression of the acidity and alkalinity of a solution and has a scale that generally ranges from about 0 to 14. pH 7 is neutral; <7 is acidic; and >7 is alkaline. [Journal of Physical Chemistry B; v102; 1002-4; 1998.] [Organometallics; v15; 5551-67; 1996.]

Phenol - 1) A corrosive poisonous crystalline acidic compound present in coal tar and wood tar that in dilute solutions is used as a disinfectant and 2) any of various acidic compounds analogous to phenols and regarded as hydroxyl derivatives of aromatic hydrocarbons. When coal and wood are burned for energy, phenols are released into the atmosphere. [Merriam Webster's Collegiate Dictionary, 10th edition, 1993, p.871.] [Industrial and Engineering Chemistry; v38; 139; 1999.]

Photic Zone - In the ocean (or in lakes) this is the area near the surface with enough light to support photosynthesis. In this zone, both the chemical and biological activity can be enhanced by penetrating solar radiation. This zone is about 20 meters in depth in the ocean. In the upper surface of this zone, the marine photochemistry is most vigorous. Changes in the ultraviolet light content penetrating this region because of changes in the UV-blocking ability of the ozone layer may create unexpected biological results there. [Atmospheric Change; T. E. Graedel and Paul J. Crutzen; Page 179; 1993; W. H. Freeman and Company; New York.] [Climate; M.R.Rampino et; Page 334; 1987; Van Nostrand Reinhold Company Inc; New York.] [Applied Geochemistry; v22; 736-759; 2007.]

Photo-aging - The accelerated aging of skin due to long-term exposure to sun light particularly UV-B; the symptoms include loss of skin elasticity, wrinkles, altered pigmentation, lowered amounts of collagen and connective tissue. [Accounts of Chemical Research; v33; 307-313; 2000.], [Analytical Chemistry; v70; 707-715; 1998.]

Photochemical Smog - Natural and artificially emitted hydrocarbons in the presence of oxides of nitrogen undergo photochemical reactions which produce a cloud of toxic chemicals including ozone and a variety of harmful chemical gaseous and particulate agents. This process is powered by sunlight and some of the products, such as ozone, reach a peak soon after photon flux from the sun reaches a maximum, around midday. The thermal inversions often associated with some cities can lead to a dangerous buildup of smog in urban areas. Human deaths have been attributed to photochemical smog since the Industrial Revolution in cities such as London and New York. [Science; v.241; 1473; 1988.] [Atmospheric Environment. Part A, General Topics; v.26A; 625; 1992.] [Science; 315; 772-773; 2007.]

Photodissociation - This is a specific type of photolysis reaction, in which the destruction of a molecule is initiated strictly by solar energy. [The Astrophysical Journal; v334; 771; 1988.] [The Journal of Physical Chemistry; v98; 1369; 1994.] [Science; v315; 84-87; 2007.]

Photolysis - The destruction of a molecule by electromagnetic radiation, which provides the energy required for a constituent atom to break the chemical bonds between it and the other atoms comprising the molecule. [Environmental Science and Technology; v.28; p.1300; 1994.] [Review of Scientific Instruments; v59; 1307; 1988.] [Science; 312; 1637-1640; 2006.]

Photon - A particle that has no rest mass, no electrical charge and whose energy is determined by its electromagnetic wavelength. A photon is considered to be an amount of electromagnetic radiation energy that is proportional to the frequency of that radiation. It may also be considered as a particle of light with energy, hv, where h is Planck's constant and v is the frequency of light. [New Scientist; v143; 16-17; 1994.] [Science; v262; 1008-1009; 1993.] [Atmospheric Science; J. Wallace and P. Hobbs; page 281; 1977; Academic Press, Inc; New York.]

Photostationary State - This describes a condition in which there is equilibrium in a photochemical reaction. For this condition to take place the rate of photodissociation or rate of chemical reaction of one or more of the reactants has to be equal to the rate of their recombination or reformation. The reactions producing ozone in the atmosphere under certain conditions are described this way. For instance, the three important tropospheric reaction involving the formation and consumption of ozone are:

O3 + NO -------> O2 + NO2 (ozone consumption by NO)

NO2 + hv -------> O + NO (NO2 photolysis)

O2 + O ----M---> O3 (ozone formation)

At night in the clean troposphere, the concentration of NO is very low and so O3 consumption is very slow, and therefore ozone's concentration stays relatively constant overnight even though ozone is no longer being produced. Likewise in polluted, urban settings at night, as before, ozone is no longer being produced but NO's concentration at the end of the day can be quite high, and so O3 in that setting can be completely destroyed overnight. There are, therefore, some concentrations of NO, NO2, sunlight, and O3 that would interact according to the equations above--and given tropospheric reaction rates and sunlight intensities--would yield a constant concentration of ozone. This would be the photostationary state concentration of ozone; however, it is important to note that this concentration--if no other reagents are considered and at normal tropospheric temperatures and sunlight intensities--is too low to account for the common ground-level ozone concentrations routinely found in polluted cites like Houston, Texas or Beijing, China. Instead, there must be other means of NO oxidation to NO2 besides oxidation by ozone ocurring to produce the O3 levels that are wide spread in highly polluted environments. And there are: peroxy compounds like methyl peroxy radical, hydroperoxy radical, and other volatile organic compounds are also involved in reactions that yield ozone in cities all over the planet. [Journal of the American Chemical Society; v125; 13684-85; 2003.] [Journal of the American Chemical Society; v124; p8800-8802; 2002.] [Atmospheric Environment; v40; 3230-3239; 2006; DOI:10.1016/j.atmosenv.2006.02.002]

Photosynthesis - Photosynthesis is a biological process which plays a vital role in cycling the atmosphere's carbon dioxide, while simultaneously producing oxygen and other complex substances. Green plants, with chlorophyll, utilize the sun's energy to convert carbon dioxide and water into the plant biomass while oxygen that is released into the atmosphere. [Science News; v146; 23; 1994.] [Quarterly Review of Biology; v69; 294-295; 1994.] [The Atmosphere; page 461; 1982; Prentice Hall Inc.; Englewood Cliffs, New Jersey.] [Global Patterns: Climate, Vegetation, and Soils; Wallace Akin; page 6; 1991; University of Oklahoma Press; Norman.] [The Green Encyclopedia; Irene Franck and David Brownstone; page 244; 1992; Prentice Hall; New York.]

Planck's Law - This is a derived formula, from the German physicist Max Planck, that portrays the amount of radiation emitted by a blackbody as theoretically determined by its temperature. It is an equation that produces a curve, termed Planck's blackbody radiation curve, which illustrates that the warmer a body is, the greater is its blackbody emission at each wavelength and the shorter is the wavelength at which emissions peak. [An Introduction to Three-Dimensional Climate Modeling; Warren Washington and Claire Parkinson; page 13; 1986; University Science Books; Mill Valley, California.] [Atmospheric Science; John Wallace and Peter Hobbs; pages 281 and 287; 1977; Academic Press, Inc; New York.]

Plankton - Plankton are forms of marine, organic life that gather vital energy for life through photosynthesis. Since they are very low on the food chain, they are vital to all marine life. They are also vital to the atmosphere in that they consume large amounts of carbon dioxide, which contribute to enhanced global warming when excess amounts are present. Plankton are considered to be one of the more important contributors of oxygen to the atmosphere. [Sea Frontiers; v40; 12-13; 1994.] [New Scientist; v143; 17; 1994.] [Understanding and Controlling Air Pollution; Howard Hesiceth; page 131; 1972; Ann Arbor Science Publishers; Ann Arbor, Michigan.] [The Green Encyclopedia; Irene Franck and David Brownstone; page 245; Prentice Hall; New York.]

Plate Tectonics - The process of planetary surface plate formation, movement, interaction, and destruction. The consequence of this process is that many regions of the planet are situated near interacting--and slowly moving--plates. The process causes earthquakes such as those along the West Coast of the United States and in Japan. [Environmental Science and Technology; v7; 562; 1973.] [Environmental Science and Technology Research; v28; 2233-41; 1994.]

Pleistocene - An epoch in Earth history from about 2-5 million years to 10,000 years ago. Also refers to the rocks and sediment deposited in that epoch. [Environmental Science and Technology; v40; 1757-63; 2006.] [Environmental Science and Technology; v37; 1528-34; 2003.]

Plume - A plume is a visible smoke-like structure, which may contain pollutants emitted from an exhaust or smoke stack and released into the atmosphere. This elongated band of smoke has changing characteristics that vary with its local environmental conditions. These conditions may include the physical and chemical nature of the pollutant, weather conditions and downwind topography. [World Press Review; v41; 24; 1994.] [Journal of Applied Meteorology; v33; 996-1016; 1994.] [Air Quality; Thad Godish; pages 58-64; 1985; Lewis Publishers, Inc; Chelsea, Michigan.]

Point Source - Pollutants which are put into the atmosphere by stationary objects, such as refineries, power plants, mills, and the like. In Texas any source that emits more than one ton in a calendar year is considered a point source. [Biotechnology Progress; v10; 344; 1994.] [Environmental Science and Technology; v27; 2919; 1993.]

Polar Stratospheric Clouds (PSCs) - See stratospheric clouds.

Polar Vortex - This is a phenomenon that occurs during the polar winter in which stratospheric air moves in a circular motion, with a volume of relatively still air in its center. The temperature in the vortex is approximately -130 degrees F (-80 degrees C), which assists in the formation of polar stratospheric clouds. Though usually more prolonged and colder over Antarctica, the Arctic polar vortex does form to a degree, and when the temperatures there are coldest and the vortex persists, Arctic stratospheric ozone destruction on Arctic polar stratospheric clouds has also been observed. [Science; v251; 46-52; 1991.] [Journal of the Atmospheric Sciences; v51; 2973-2994; 1994.] [Elements: Air; Michael Allaby; page 160; 1992; Facts on File Inc; New York.] [Antarctica; Carl Eklund and Joan Beckman; page 83; 1963; Holt, Rinehart and Winston, Inc; New York.] [Science; v296; 895 - 899; 2002; DOI:10.1126/science.1069270]

Pollutants - A pollutant may be considered as any substance, usually an unwanted by-product or waste, that is released into the environment as a result of (human) activities that alter the chemical, physical and biological characteristics of the environment. These substances may be found in any of the solid, liquid or gas phases. Their long-term effects are difficult to predict and depend upon future human or cultural judgments. [Mechanical Engineering; v116; 2973-2994; 1994.] [Science News; v146; 198; 1994.]

Polychlorinated Biphenyls (PCBs) - A family of chemical compounds formed by the addition of chlorine to a biphenyl system (a dual-ring structure comprising two benzene rings linked by a single carbon-carbon bond). They are categorized as a TOMP (Toxic Organic Micro Pollutant). PCBs are released into the atmosphere through the incomplete combustion of fuel or the processing of old electrical transformers or capacitors and are particularly long-lived, with atmospheric destruction of PCBs usually caused by reaction with OH radicals. The ultraviolet wavelengths that destroy PCBs do not make it to the troposphere because they are blocked by the ozone layer, but photolysis can occur in the upper atmosphere. Bioprocessing by organisms in soil and water is a much more common, though very slow destruction route for PCBs. PCBs have been found in some organism on all the earth's continents. [Atmospheric Environment; v41; 452-464; 2007.] [Environmental Pollution; v97; 295-301; 1997.]

Polynuclear Aromatic Hydrocarbons - (PAHs) These compounds are large ring aromatic hydrocarbons that are molecules containing carbon and hydrogen. It could also be any large ring that consists of five or more cyclic compounds of carbons and any elements that may be bonded to the ring. They usually exist in nature in low amounts. Many times these hydrocarbons exist within the atmosphere in the aerosol phase from combustion processes. [Analytical Chemistry; v.66; pages 4288-4294; 1994.] [Analytical Chemistry; v.66; pages 1808-1816; 1994.]

Positive Crankcase Valve - See PCV systems.

Precambrian - All geologic time from the beginning of Earth history to 570 million years ago. Also refers to the rocks that formed in that epoch. [Environmental Science and Technology; v31; 3461-67; 1997.] [Environmental Science and Technology; v37; 437-45; 2003.]

Precipitation - What often occurs when clouds form upon reaching 100% relative humidity. If condensation nuclei are present, liquid or solid particles of water will form. When this material becomes heavy enough to fall towards the ground, it is known as the common phenomenon snow, rain, sleet, or hail. [Nature; v.372; pages 250-252; 1994.] [Environmental Science and Technology; v.28; pages 1459-1466; 1994.]

Primary Particles - Small amounts of condensed matter in the atmosphere, often originated from the incomplete combustion of coal and oil or from dust storms and also generated from anthropogenic sources like mining or metallurgy. Some portion of these particles are suspended in air--depending on atmospheric conditions--causing the warming or the cooling of atmosphere by changing the amount of radiation that reaches the earth's surface. Particles composed of black carbon, or soot for instance, warm the atmosphere by absorbing sunlight and heating the surrounding air. Other particles scattering sunlight back to space resulting in a cooling of the atmosphere. [Atmospheric Environment; v34; 3805-3811; 2000; DOI:10.1016/S1352-2310(00)00139-4]

Primary Pollutant - This refers to the types of pollutants that are either found in the atmosphere or on the ground and are emitted directly from some sources such as automobile tailpipes or smoke stacks. This is contrasted with secondary pollutants which in and of themselves are not directly emitted from a source. Instead they are created from chemical and photochemical reactions of primary pollutants. Nitrogen monoxide is an example of a primary pollutant and ozone is an example of a secondary pollutant. [Energy and Fuels; v17; 1510-21; 2003.] [Environmental Science and Technology; v40; 5804-10; 2006.]

Propagation - In chemical terms, a propagation step is any step but the first, initial step, in a chain reaction (a series of chemical reactions in which the first reaction causes the second which causes the third, which causes the fourth, etc). [Journal of Molecular Structure: THEOCHEM. 540, 53-61 (2001)] [Sensors and Actuators B: Chemical; 62; 143-147; 2000.]

2-Propenal - Commonly referred to as acrolein, this compound is found from several sources such as hydrocarbon burning, emission from fuels, and tobacco smoke; it is also a secondary pollutant in the atmosphere from reactions with 1,3-butadiene. [Atmospheric Environment; v40; 5087-5096; 2006.]

2-Propenenitrile - CH2CHCN, a bad smelling, colorless liquid that is used in plastics, and when these plastics are burned they produce fumes that are carcinogenic because of the 2-propenenitrile. [International Journal of Mass Spectrometry; v262; 88-100; 2007.]

Propionaldehyde- C3H6O, a colorless liquid that enters the atmosphere by emissions from the manufacture of plastics, synthesis of rubber, and as a disinfectant and a preservative. [J. Phys. Chem; v.105 pages 9689 -9696] [Journal of Chemical and Engineering Data; v44; 1071-1075, 1999.]

n-Propylbenzene - C9H12, A colorless or light yellow liquid. It is a primary solvent for cellulose acetate and is used in textile dying. It is naturally found in petroleum and bituminous coal and its main source is from the combustion of gasoline, landfill leaching and general use of asphalt. It has a molecular weight of 120.9 g/mol and is also known as isocumene or phenylpropane. It has a melting point of -99°C, a boiling point of 159°C, and a vapor pressure of 3.42 mmHg at 25°C. n-propylbenzene is flammable and incompatible with strong oxidizing agents. It is harmful if swallowed and is a respiratory irritant. N-Propylbenzene degrades photo-chemically with hydroxyl radicals in the atmosphere and has a half-life of 2.7 days. [The Journal of Chemical and Engineering Data; v40; 598-600; 1995.] [The Journal of Organic Chemistry; v60; 2430-65; 1995.]

Pyrodenitrification - This is best defined as way that nitrogen is lost or emitted by the use of heat or radiation, mainly, from the sun. This can occur in the air or on the ground around vegetative regions. It is less likely to occur in arid regions, but it is possible. [Soil Science Service of America; v.57; pages 1013-1020; 1993.] [Nature; v.349; pages 319-321; 1993.]

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Quantum Yield - A measure of how efficient an emission process is. The quantum yield is a ratio of absorbed photons and photons used up in the chemical process. Quantum yield is usually dependent on temperature, pressure, and wavelength. [Chemosphere; v51; 175-179; 2003.] [Atmospheric Environment; v37; 1835-1851; 2003.] [Science; v299; 1566-1568; 2003.]

Quasi-Biennial Oscillation - Periodic variation in the direction, either easterly or westerly, of tropical lower stratospheric winds. The direction changes every 26 months. [Environmental Science and Technology; v9; 615-17; 1975.] [Science; v243; 923-925; 1989.] [Chemical Research; v103; 4509-32; 2003.]

Quaternary - The period of Earth's history from about 2 million years ago to the present; also, the rocks and deposits of that age. [Organic Letters; v7; 1435; 2005.] [Journal of the American Chemical Society; v122; 192; 2000.] [Science; v316; 66-69; 2007.]

Quicklime - Also referred to as calcium oxide (CaO), lime, or calx. The physical appearance of CaO is white, caustic, and solid at room temperature. Calcium oxide is simply produced by heating the calcium carbonate (CaCO3) at high temperatures (~2000 F), and CO2 is released as byproduct:

CaCO3 + Heat -------> CaO + CO2 (g)

Because of its physical and chemical qualities calcium oxide can be utilized in a variety of applications such as glass, fiberglass, the steel and food industries, as well as the plastic and rubber industries. Large amounts of lime are used to make cement making this process a significant contributor to anthropogenic CO2 emissions. [ACS symposium series; v515; 223-240; 1992; DOI:10.1021/bk-1992-0515.ch018]

Quinones - A federal hazardous air pollutant deemed toxic in 1993 has a generic molecular formula of C6H4O2 and belong a class of compounds that are derived from aromatics resulting in a fully conjugated dione. Quinones are all solids under normal conditions, characterized by yellow crystals, and have an odor similar to that of chlorine.  Quinone is emitted naturally by some arthropods and many insects, and is used in the manufacturing of fungicides, and in photography, as a chemical intermediate, as well as in tobacco products.  Quinone are oxidizing agents and exists in the atmosphere to varying degrees in the gas phase with an atmospheric half-life of ~3 hours, and are predominantly lost by reaction with hydroxyl radicals.  Quinones react slowly with ozone. [Biochemica et Biophysica Acta (BBA)-Bioenergetics; v1797; 1587-1605; 2010; DOI:10.1016/j.bbabio.2010.06.007]

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