Skip to content

Glossary & Abbreviations

Ambient Air- The air occurring at a particular time and place outside of structures. Often used interchangeably with outdoor air.

Area-wide Sources (also known as "area" sources)- Stationary sources of pollution (e.g., water heaters, gas furnaces, fireplaces, and woodstoves) that are typically associated with homes and non-industrial sources.

Attainment Area- A geographic area in which levels of a criteria air pollutant meet the health-based primary standard (national ambient air quality standard, or NAAQS) for the pollutant. An area may have an acceptable level for one criteria air pollutant, but may have unacceptable levels for others. Thus, an area could be both attainment and nonattainment at the same time.

Best Available Control Technology/Best Available Control Measure (BACT/BACM)- The most up-to-date methods, systems, techniques, and production processes available to achieve the greatest feasible emission reductions for given regulated air pollutants and processes.

Criteria Pollutants- The 1970 amendments to the Clean Air Act required EPA to set National Ambient Air Quality Standards for certain pollutants known to be hazardous to human health. EPA has identified and set standards to protect human health and welfare for six pollutants; ozone, carbon monoxide, total suspended particulates, sulfur dioxide, lead, and nitrogen oxide. The term, "criteria pollutants" derives from the requirement that EPA must describe the characteristics and potential health and welfare effects of these pollutants.

Emission Inventory- A catalog or listing of emissions from a source, usually based on measurements, calculations, or other information regarding pollutant information.

Federal Clean Air Act (FCAA)- A federal law passed in 1970 and amended in 1977 and 1990 which forms the basis for the national air pollution control effort.

µg/m3- A concentration of an air pollutant (e.g. ozone) is given in micrograms (one-millionth of a gram) per cubic meter air.

Maintenance Area- An area that had previously been designated a nonattainment area, but now meets applicable air quality standards.

Memorandum of Understanding (MOU)- A document describing a bilateral or multilateral agreement between parties. It expresses a convergence of will between the parties, indicating an intended common line of action.

Mobile Sources- Moving objects that release pollution, mobile sources include cars, trucks, buses, planes, trains, motorcycles and gasoline-powered lawn mowers.

Nonattainment- A geographic area that does not meet, or exceeds, established air pollution levels.

Parts per Million (ppm)- A ratio of the amount of one substance to the amount of another, expressed as a unit of solute dissolved in one million units of solution. It denotes the number of units of one substance relative to one million units of another substance.

Primary Standards- National ambient air quality standards designed to protect human health with an adequate margin for safety.

Public Notice- Notification to the public of a pending permit and inviting public comment.

Secondary Standards- National ambient air quality standards designed to protect welfare, including effects on soils, water, crops, vegetation, man-made materials, animals, wildlife, weather, visibility, and climate; damage to property, transportation hazards, economic values, and personal comfort and well-being.


ADEC - Alaska Department of Environmental Conservation
BACM - best available control measure
BACT - best available control technology
CAA - Clean Air Act
CARB - California Air Resources Board
CFR - Code of Federal Regulations
CNG - compressed natural gas
CO - carbon monoxide
EI - Emissions Inventory
EPA - U.S. Environmental Protection Agency
FIP - Federal Implementation Plan
g/hp-hr - grams per horsepower-hour
GIS - Geographic Information System
g/mi - grams per mile
GVWR - gross vehicle weight rating
HAP - hazardous air pollutant
HC - hydrocarbon
HDD - heavy-duty diesel
HDDV - heavy-duty diesel vehicle
HDV - heavy-duty vehicle
hp - horsepower
km - kilometer
LDT - light-duty truck
LED - low-emission diesel
LEV - low-emission vehicle
LNG - liquefied natural gas
LSG - low-sulfur gasoline
m - meter
MACT - maximum achievable control technology
MPH - miles per hour
MY - model year
NAAQS - National Ambient Air Quality Standards
NOx - nitrogen oxides
O3 - ozone
OBD - onboard diagnostics
OTAQ - the EPA 's Office of Transportation and Air Quality
Pb - lead
PCV - positive crankcase ventilation
PM - particulate matter
PM2.5 - particulate matter smaller than 2.5 microns
PM10 - particulate matter smaller than 10 microns
ppb - parts per billion
ppm - parts per million
QA/QC - quality assurance / quality control
RACT - reasonably available control technology
RFG - reformulated gasoline
RPM - revolutions per minute
SCC - source classification code
SIP - State Implementation Plan
SO2 - sulfur dioxide
TCM - transportation control measures
TIP - Transportation Implementation Plan
TPD - tons per day
TPY - tons per year
TSP - total suspended particulate
VID - Vehicle Identification Database
VIN - Vehicle Identification Number
VIR - vehicle inspection report
VMT - vehicle miles traveled
VOC - volatile organic compounds