AIR POLLUTION GLOSSARY

• Absorption The taking up or assimilation of one substance by another, where the two substances chemically combine.
• Adsorption The adhesion of a thin film of liquid or gas to a solid substance.
• Aerosol A colloidal system in which the dispersed phase is composed of either solid or liquid particles, and in which the dispersion medium is some gas, usually air. Generally less than one micrometer in size.
• Air Toxics Any air pollutant for which an NAAQS does not exist (i.e. excluding ozone, carbon monoxide, PM-10, sulfur dioxide, nitrogen dioxide) that may reasonably be anticipated to cause cancer, developmental effects, reproductive dysfunctions, neurological disorders, heritable gene mutations or other serious or irreversible chronic or acute health effects in humans.
• Agglomeration The growth of a particle by collision with and assimilation of other particles. Ordinarily, the connotation is that all particles are solid.
• Air Quality The composition of air with respect to quantities of pollutants therein; used most frequently in connection with "standards" against which the contribution of the particular source can be compared.
• Aromatics A type of hydrocarbon, such as benzene or toluene, added to gasoline in order to increase octane. Some aromatics are toxic.
• Attainment Area An area considered to have air quality as good as or better than the NAAQS as defined in the Clean Air Act. An area may be an attainment area for one pollutant and a non-attainment area for others.
• Best Available Control Measure (BACM) A term referring to the "best" measures (according to EPA) for controlling small or dispersed sources of particulate matter, such as roadway dust, woodstoves, and open burning.
• CFC-12 The chlorofluorocarbon with the trademark name of Freon commonly used in refrigeration and automobile air conditioning.
• Chlorofluorocarbons (CFCs) A family of inert, nontoxic, and easily-liquefied chemicals used in refrigeration, air conditioning, packaging, insulation, or as solvents or aerosol propellants. Because CFCs are not destroyed in the lower atmosphere, they drift into the upper atmosphere where the chlorine is released by ultra violet radiation and destroys ozone.
• Clean Fuels Blends and/or substitutes for gasoline fuels including compressed natural gas, methanol, ethanol.
• Coagulation Generally, any process that converts numerous small particles into a smaller number of larger particles.
• Coalescence The merging of two liquid particles into a single particle.
• Dispersion The removal (by whatever means) of pollutants from the atmosphere over a given area; or the distribution of a given quantity of pollutant throughout an increasing volume of atmosphere.
• Dust Solid materials suspended in the atmosphere by turbulence. Larger than aerosol particles. Dust can be from volcanic eruptions, sea salt spray, blowing solid particles, plant pollen and bacteria, smoke and ashes of forest fires or from industry, etc.
• Federal Implementation Plan (FIP) A federally implemented plan to achieve attainment of an air quality standard, used when a state is unable to develop an adequate plan.
• Fly Ash Ash particles, frequently in the form of small, irregular flakes, that escape into the atmosphere and quite rapidly settle to the ground.
• Fume Very fine particles, predominantly less than one micrometer in diameter.
• Fumigation The phenomenon in which pollutants, that had remained aloft in stratified, stable air, are brought rapidly to the ground level when the air destabilizes.
• Halons A family of compounds containing bromine used in fighting fires, whose breakdown in the atmosphere depletes stratospheric ozone.
• Haze Fine dust or salt particles dispersed through a portion of the atmosphere. They can not be individually seen but together they reduce the horizontal visibility.
• HCFCs Chlorofluorocarbons that have been chemically altered by the addition of hydrogen, and which are significantly less damaging to stratospheric ozone than other CFCs.
• Hydrocarbon A group of compounds that consist solely of the elements carbon and hydrogen.
• Maximum Achievable Control Technology (MACT) Emissions limitations based on the best demonstrated control technology or practices in similar sources to be applied to major sources emitting one or more of the listed toxic pollutants.
• Montreal Protocol An international environmental agreement to control chemicals that deplete the ozone layer. The protocol which was renegotiated in June 1990, calls for a phase-out of CFCs, halons, and carbon tetrachloride by the year 2000, a phase-out of chloroform by 2005, and provides financial assistance to help developing countries make the transition from ozone-depleting substances. Further amendments in 1992 moved the deadline to halt production of most ozone-destroying chlorofluorocarbons up to 1996.
• National Ambient Air Quality Standard (NAAQS) Air quality standard determined by EPA.
• Oxygenated Fuels Gasoline which has been blended with alcohols or ethers that contain oxygen in order to reduce carbon monoxide and other emissions.
• Photochemical Smog Smog wherein secondary pollutants are produced by photochemical reactions.
• PM-10 A standard for measuring the amount of solid or liquid matter suspended in the atmosphere (Particulate Matter). Refers to the amount of particulate matter under ten micrometers in diameter. The smaller PM-10 particles penetrate to the deeper portions of the lung, affecting sensitive population groups such as children and people with respiratory diseases.
• Prevention of Significant Deterioration (PSD) A part of the US Clean Air Act based on the principle that clean areas should remain clean, thus air pollution may increase only a small amount.
• Primary Air Pollution Standard Level of air quality necessary, with adequate margin of safety, to protect the public health.
• Primary Pollutant An air pollutant having the same form as when it was emitted at its source.
• Rainout (snowout) In-cloud scavenging of air pollution by cloud or precipitation.
• Reasonably Available Control Technology (RACT) An emission limitation on existing sources in non-attainment areas, defined by EPA in a Control Techniques Guideline (CTG) and adopted and implemented by States. The guidelines contain information on both the economic and technological feasibilities of available techniques.
• Residual Risk The quantity of health risk remaining after application of MACT.
• Sanctions Actions taken against a state or local government by the Federal government for failure to plan or to implement a SIP. Examples include withholding of highway funds and a ban on construction of new sources.
• Secondary Air Pollution Standard Level of air quality necessary to protect the public welfare from known or anticipated adverse effects of pollutant.
• Secondary Pollutant An air pollutant that has undergone a chemical change since having been first emitted into the atmosphere; or a pollutant created by reactions involving primary pollutants.
• Stage II Controls Systems placed on service station gasoline pumps to control and capture gasoline vapors during automobile refueling.
• Smoke Foreign particles in the atmosphere resulting from a combustion process.
• Smog Originally smoke plus fog, but now often with or without fog. Some visible manifestation is almost always implied.
• Soot Fine particles of carbon produced by the incomplete combustion of carbonaceous fuels.
• State Implementation Plan (SIP) Document prepared by states, and submitted to EPA for approval, which identifies actions and programs to be undertaken by the state and its subdivisions to implement their responsibilities under the Clean Air Act.
• Transportation Control Measures (TCMs) Steps taken by a locality to adjust traffic patterns (e.g. bus lanes, right turn on red) or reduce vehicle use (e.g. ridesharing, high-occupancy vehicle lanes) to reduce vehicular emissions of air pollution.
• Turbidity Any condition of the atmosphere (except clouds) which reduces its transparency to radiation, especially to visible radiation: smoke, haze, dust, scintillation effects.
• Volatile Organic Compounds (VOCs) A group of chemicals that react in the atmosphere with nitrogen oxides in the presence of heat and sunlight to form ozone; does not include methane and other compounds determined by EPA to have negligible photochemical reactivity. Examples of VOCs include gasoline fumes and oil-based paints.
• Washout Sweeping out of airborne particles by rain or snow (below cloud).