Acidification — The process by which rivers, lakes, rain, and other natural features become affected by excess acid. For example, nitrogen dioxide may form toxic organic nitrates, which contribute to acid rain and the acidification of ground and surface water.
Air Toxics — Air toxics include any air pollutant for which a National Ambient Air Quality Standard does not exist (i.e., excluding ozone, carbon monoxide, PM-10, sulfur dioxide, and nitrogen oxide) 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.
Ambient Air — The portion of the atmosphere, external to buildings, to which the public has access.
Ambient Air Quality — A physical and chemical measure of pollutant concentrations in the ambient atmosphere. The quality is usually determined over a specific time period.
Attainment Area — A geographic area in which levels of a criteria air pollutant meet or are better than the health-based primary standard (National Ambient Air Quality Standard, or NAAQS). A single area could be designated attainment for one pollutant and nonattainment for another.
Best Available Control Technology (BACT) — An emission limit based on the maximum degree of reduction for each pollutant regulated by the Clean Air Act. The permitting authority, taking into account energy, environmental and economic impacts determines what emission limits facilities should achieve in an attainment area on a case-by-case basis by considering production processes, available methods, systems, and techniques.
British Thermal Units (BTUs) — The amount of heat necessary to increase the temperature of one pound of water one degree Fahrenheit at a specified temperature.
Carcinogenic Substances — Cancer-causing substances.
Cardiovascular — Pertaining to or involving the heart and blood vessels.
Chemical Mass Balance — A modeling technique to identify and quantify the emission sources of particulates present in an area of interest.
Clean Air Act — A law enacted by Congress to protect and enhance the quality of the nation's air resources, promote public health and welfare, and enhance the productive capacity of its population.
Criteria Air Pollutant — A pollutant for which EPA has established a National Ambient Air Quality Standard under Section 109 of the Clean Air Act. Present criteria pollutants include carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter equal to or smaller than 10 microns (PM-10), fine particulate matter smaller than or equal to 2.5 microns (PM-2.5.), and sulfur dioxide.
Dispersion — The action of the atmosphere that mixes an ambient air pollutant, thereby reducing the concentration.
Hydrocarbons — Compounds composed of carbon and hydrogen atoms.
Inversion — A meteorological condition in which the temperature of the atmosphere rises with increased elevation instead of falling, creating a stagnant layer of air near the ground.
Lowest Achievable Emission Rate (LAER) — A requirement applying to proposed new or modified major stationary sources of pollution in nonattainment areas. LAER means the "rate of emissions that reflect the most stringent emission limitation contained in the SIP of any state for such class or category of source or the most stringent emission limitation which is achieved in practice . . . whichever is more stringent."
Meteorological Conditions — Atmospheric conditions such as wind speed, wind direction, temperature, and atmospheric stability (mixing of the air).
Micron — Also referred to as a micrometer, a micron is a metric unit of measure equal to one millionth of a meter. This unit is often used for describing sizes of airborne particles.
Montana Ambient Air Quality Standards (MAAQS) — Minimum standards set by DEQ for air pollutants, including criteria air pollutants, that must be met throughout Montana.
Montana Department of Environmental Quality (DEQ) — The department within the State of Montana government that regulates pollution to the air, water, and land.
Montana Board of Environmental Review — Seven members, appointed by the Governor, who are representative of the geographic areas of the state. The membership must include persons who have expertise or backgrounds in the following areas: law, hydrology, local government planning, and environmental sciences. One of the members must be either a county health officer or a medical doctor. The Board is both a quasi-legislative and quasi-judicial board. Its duties include rulemaking and determining appeals of department decisions.
Montana Department of Health and Environmental Sciences (MDHES) — Created by the Executive Reorganization Act of 1971, which also established the Board of Health and Environmental Scienes (predecessor of the Montana Board of Environmental Review) as a separate, quasi-judicial body that concurs (or not) in issuance of certain licenses, permits, variances, etc. The Board may also adopt rules, regulations, and standards. The Board consists of seven members, appointed by the Governor.
National Ambient Air Quality Standards (NAAQS) — Minimum standards set by EPA developed for criteria air pollutants that must be met everywhere in the country.
National Emission Standards of Hazardous Air Pollution (NESHAP) — Federal standards developed by industrial source categories that limit hazardous air pollutant emissions.
New Source Performance Standard (NSPS) — Federal standards developed for industrial source categories to limit criteria air pollutant emissions.
Nonattainment Area — A geographic area defined by EPA no meeting the NAAQS for a given pollutant. A single geographic area may have acceptable levels of one criteria air pollutant, but unacceptable levels of other criteria air pollutants.
Oxidants — Substances that combine with oxygen.
Oxygenated Fuel (oxyfuel) — A special type of gasoline with added oxygen in order to burn more completely than regular gasoline in cold start conditions. More complete burning results in a reduction of carbon monoxide and particulates. In some parts of the country, carbon monoxide released from cars starting up in cold weather is a major contribution to air pollution.
Particles — Any solid or liquid matter larger than a molecule (less than 0.0002 micron diameter). It is composed of settleable matter (which will settle as dust within a reasonable period of time) and suspended matter (which remains suspended in the atmosphere until washed out by precipitation, deposited by impaction, or some other process).
Particulate Matter — Finely divided solids or liquids ranging in size from less than 0.1 micron to 50 microns in aerodynamic diameter. Gasses can form particles in the atmosphere through chemical reactions.
Pollutant Source — Any area, mobile, or stationary point source from which air pollutants are released. A stationary pollutant source can be a power plant, factory, dry cleaning business, gas station, or farm. An area source can be roadways and large geographic areas such as residential wood burning. Mobile sources are cars, trucks, and other motor vehicles.
Prevention of Significant Deterioration (PSD) — A permitting program to prevent significant increases in air pollution to maintain the area's air quality that is already better than National Ambient Air Quality Standards (attainment areas).
Pulmonary — Pertaining to the lungs.
Regional Haze Rule — Revised the existing federal visibilty regulations to integrate certain provisions addressing regional haze impairment that will apply to all states. The resulting regulations will reflect a comprehensive visibility protection program for all Class I areas except those on reservations.
Smog — A combination of smoke and other particulates, ozone, hydorcarbons, nitrogen oxides, and other chemically reactive compounds that under certain conditions of weather and sunlight may result in a brown haze that causes adverse health effects.
State Implementation Plan (SIP) — A document prepared by each state describing existing air quality conditions and measures which will be taken to attain and maintain national ambient air quality standards.
Stagnation — With respect to air pollution, stagnation is the persistence of a given volume of stable air over a region, resulting in an abnormal buildup of pollutants from sources within the region.
Topography — The physical features of a place or region.
United States Environmental Protection Agency (EPA) — The federal government agency that regulates pollution to the air, water, and land.
Volatile Organic Compounds (VOCs) — Compounds made up of carbon molecules that participate in atmospheric reactions caused by sunlight and heat.
