| Section A | A index | 311-319 of 917 terms |
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air pollution control—The process of attempting to limit the amount of air pollution by regulating the emission of pollutants or their precursors. Control strategies are alternative long-term policies that could reduce air pollution, as projected using air-quality modeling. For primary pollutants such as sulfur dioxide, control strategies include burning cleaner low-sulfur coal, scrubbing sulfur dioxide from the combustion products before releasing them into the atmosphere, or changing to alternative fuels or processes. For secondary pollutants such as ozone that are not emitted directly but are created in the lower atmosphere by a complex series of chemical and photochemical reactions involving NOx and volatile hydrocarbons, control is achieved by changing the emissions of one or both of the primary reactants.
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air pollution episode—1. An extended period of a high concentration of pollutants in the atmosphere.2. A public alert or notification of unhealthful air quality. In the U.S., the degree of alert is often based on the pollutant standards index (PSI): | Stage 1 episode or alert, for 200 ≤ PSI < 275. Public recommendation: avoid strenuous activities. Children and elderly people advised to stay indoors. |
| Stage 2 episode or alert, for 275 ≤ PSI < 400. Public recommendation: cease all physical activity, and stay indoors. Industry can be ordered to reduce emissions, and employees forced to carpool or use mass transportation for their necessary travel. |
| Stage 3 episode or alert, for PSI ≥ 400. Everyone ordered to remain at home with windows closed. Minimize physical exertion and avoid driving vehicles. Automobile travel could be restricted and industries ordered to reduce emissions. |
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air pollution meteorology—The subdiscipline of meteorology devoted to the study of air pollution. Topics include sources of pollutants, emission rates, plume rise, fallout, dry and wet deposition, chemistry, precipitation scavenging, dispersion (molecular diffusion and turbulent transport), short- and long-range transport (advection), trapping, venting by cumulus clouds, complex terrain and mesoscale circulations, receptors, impact on society, alerts and episodes, policy and regulation, modeling, prediction, control, and climate change.
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air pollution—The presence of substances in the atmosphere, particularly those that do not occur naturally. These substances are generally contaminants that substantially alter or degrade the quality of the atmosphere. The term is often used to identify undesirable substances produced by human activity, that is, anthropogenic air pollution. Air pollution usually designates the collection of substances that adversely affects human health, animals, and plants; deteriorates structures; interferes with commerce; or interferes with the enjoyment of life. Compare airborne particulates, designated pollutant, particulates, criteria pollutants.
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air quality criteria—Quantitative and qualitative indications of the relationships between exposure to pollutants and effects on human health, animals, plants, and materials. These are descriptive effects of pollution as a function of concentration averaged over various time durations. A time-averaged concentration is used because exposure to a high concentration of pollutants during a short time might have an impact equivalent to an exposure to a lower concentration over a longer time. Compare air quality standards.
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air quality standards—Maximum legal concentration limits of air pollutants averaged over specified time periods. These are prescriptive. If the actual measured concentration averaged over time exceeds the legal threshold, then the event is called an exceedence. Regulations often allow a limited number of exceedences each year, with fines or penalties imposed for too many exceedences. Regions with too many exceedences are required to develop plans to improve the air quality, for example, by changing automobile fuels and gas-station equipment or increasing the use of mass transportation. In the United States, the standards are called National Ambient Air Quality Standards (NAAQS). Primary standards are designed to protect human health. Secondary standards are designed to protect crops, animals, structures, and commerce. In Canada, these legal thresholds are called National Air-Quality Objectives. Three levels of standards exist within these objectives. In ascending order of concentration limit they are Maximum Desirable Level, Maximum Acceptable Level, and Maximum Tolerable Level. Compare air quality criteria, emission standard, criteria pollutants.
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air report—(Abbreviated AIREP.) A report from an aircraft in flight prepared in conformity with requirements for position and operational and/or meteorological reporting. See pilot report.
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