Attainment Area: An area considered to have air quality that meets or exceeds the Environmental Protection Agency health standards used in the Clean Air Act.
CO: Carbon Monoxide. Carbon Monoxide is a colorless, odorless, tasteless gas formed in large part by incomplete combustion of fuel. Human activities (i.e. transportation or industrial processes) are largely the source for CO contamination.
Conformity: Process to assess the compliance of any transportation plan, program, or project with air quality implementation plans. The Clean Air Act defines the conformity process.
HC: Hydrocarbons. Hydrocarbons is a generic term referring to chemical compounds made up primarily of the elements carbon and hydrogen. All VOC are considered Hydrocarbons.
Maintenance Area: Any geographic region of the United States previously designated nonattainment pursuant to the Clean Air Act Amendments of 1990 and subsequently redesignated to attainment subject to the requirement to develop a maintenance plan under section 175A of the Clean Air Act, as amended.
National Ambient Air Quality Standards (NAAQS): Federal standards that set allowable concentrations and exposure limits for various pollutants. The Environmental Protection Agency developed the standards in response to a requirement of the Clean Air Act.
NOx: Nitrogen Oxides. Oxides of nitrogen are a collective term for all compounds of nitrogen and oxygen which includes nitrogen monoxide, nitrogen dioxide, etc.
Nonattainment Areas: Geographic areas that have failed to meet the National Ambient Air Quality Standards.
O3: Ozone. Ozone is a colorless gas with a sweet odor. Ozone is not a direct emission from transportation sources. It is a secondary pollutant formed when HC and NOx combine in the presence of sunlight. Ozone is associated with smog or haze conditions. Although the ozone in the upper atmosphere protects us from harmful ultraviolet rays, ground-level ozone produces an unhealthy environment in which to live. Ozone is created by human and natural sources.
PM10: Any material that exists as solid or liquid in the atmosphere. Particulate matter may be in the form of fly ash, soot, dust, fog, fumes, etc. Coarse particulate matter has a diameter of less than 10 micrometers.
PM2.5: Any material that exists as solid or liquid in the atmosphere. Particulate matter may be in the form of fly ash, soot, dust, fog, fumes, etc. Small particulate matter has a diameter of less than 2.5 micrometers.
SOx: Oxides of sulfur are gases that are formed when fuel that contains sulfur, such as coal and oil, is burned, and when gasoline is extracted from oil, or metals extracted from ore.
VOC: Volatile organic compounds. VOCs come from vehicle exhaust, paint thinners, solvents, and other petroleum-based products. A number of exhaust VOCs are also toxic, with the potential to cause cancer.
