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Maryland State Government Maryland Department of the Environment

Air Quality Acronyms and Glossary

  Additional Resources on Abbreviations, Acronyms, and Glossary

Click on a letter: A B C D E F G H I J K L M N O P Q R S T U V W XYZ

Note: Definitions and explanations are provided in reference to air quality.  Some definitions provided may be different and could be misused in a generic context.


A

Aerosol: Suspensions of tiny liquid and/or solid particles in the air.  Aerosols can be found naturally (from volcanic activities or dust, etc.) and/or human-made (from burning of fossil fuel and coal, etc.) but both can reduce visibility and degrade air quality.

Aethalometer: An instrument used for real-time measurement of optical absorption by aerosol particles; a measure of the attenuation of a specific wavelength of light through a quartz fiber as it loads over time.

Air Pollutant: Chemicals or other materials suspended in the air from natural or human-made processes that can threaten human health and welfare.  There are currently "Six Common Air Pollutants", also known as "Criteria Pollutants", regulated by the U.S. EPA.  Click here to learn more about Criteria Pollutants and their impacts on health and the environment.

Air Pollution: Degradation of air quality resulting from chemicals or other materials suspended in the air from natural processes or human-made.

Air Quality: Degree of purity of air to which people, natural and heritage resources are exposed.  It is routinely compared with "standards" of maximum acceptable pollutant concentrations as determined by the EPA under the Clean Air Act.  In the United States (though used in slightly different forms around the world) the degree of purity of air is expressed in a color-coded system known as Air Quality Index (AQI).

AIRS: Aerometric Information Retrieval System is a computer-based repository of air pollution data collected by EPA, state, local, and tribal air pollution agencies from thousands of monitoring stations across the continental United States, Alaska, Puerto Rico, and the Virgin Islands.  It is administered by the EPA Office of Air Quality Planning and Standards.

AQI: Air Quality Index is a color-coded index for reporting air quality information and forecast to the public.  It was originally developed by the Maryland Department of the Environment and the American Lung Association in the 1994 and was adopted by the US EPA in 1988 as part of the federal Air Quality Index (AQI) to present air quality information and forecasts to the public.

AQS: EPA's Air Quality System.  Visit TTN AIRS AQS website for details.

AQS ID/Code: 9-digit site identification number in AQS database consisting of 2-digit state code, 3-digit county code, and 4-digit site number.  For instance, the AQS code for HU-Beltsville monitoring station in Prince Georges County, MD is "24-033-0030".

ARMA: MDE's Air and Radiation Management Administration.

Atmospheric Deposition: The process by which gases and particles suspended in the air are transferred from the atmosphere to the surface of the earth.  See Dry and Wet Depositions for additional information.

Attainment: Air pollution levels at a site or a geographic extent are below (meet) the National Ambient Air Quality Standards (NAAQS).

Attainment Area: A geographic extent consisting of one or more counties where air pollution levels are below (meet) the National Ambient Air Quality Standards (NAAQS).


B

Back Trajectory: A path tracing an air-mass backward in time to determine its origin before it arrives at a particular location and time.  24-hour back trajectories are typically used in air quality analysis as a way to learn about air-mass history.  There are many trajectory and dispersion models.  One of the commonly used is the NOAA HYSPLIT model.

BAM: Beta Attenuation Mass Monitor is an instrument that measures continuous (hourly or sub-hourly) particulate matter mass.

BACT: Best Available Control Technology is a source emission limitation based on the best currently available technology producing the greatest reduction of air pollutant emissions with considerations on energy, environmental, economic, and other costs.  Major sources are required to use BACT unless it can be demonstrated that it is not feasible for energy, environmental, or economic reasons.

BART: Best Available Retrofit Technology is a source emission limitation based on the best currently available technology producing the greatest reduction of air pollutant emissions with considerations on energy, environmental, economic, and other costs.  Sources emitting air pollutants that reduce visibility including particulate matter and its constituents (NOx, SO2, VOCs, and ammonia) under the regional haze rule.  Visit EPA webpage for Visibility Regulatory Actions for more information.


C

CAA: Clean Air Act of 1970, passed by Congress authorizing the Environmental Protection Agency to establish National Ambient Air Quality Standards for pollutants shown to threaten human health and welfare. Visit CAA website for more information.

CAAA: Clean Air Act Amendments. Visit CAA website for more information.

CBSA: Core Based Statistical Area is "a collective term for both [Metropolitan and micropolitan statistical areas] metro and micro areas."  (Source: U.S. Census Bureau)

CENRAP: Central Regional Air Planning Association is one of the five organizations consisting of tribal, local, state, federal air pollution agencies, and other interested parties.  The goal of an RPO is to work collaboratively in developing regional strategies to solve air pollution, addressing regional haze, and related issues.  CENRAP includes states and tribal areas of Nebraska, Kansas, Oklahoma, Texas, Minnesota, Iowa, Missouri, Arkansas, and Louisiana.  Other RPOs include: MANE-VU, Midwest RPO, VISTAS, and WRAP.  See each listed RPO to learn more or visit EPA website on RPO for a regional map and links.

CFR: Code of Federal Regulations is the codification of the general and permanent rules of the executive departments and federal agencies.  CFR is divided into fifty volumes called "titles".  Title 40 of the CFR (referenced as 40 CFR) lists all environmental regulations.  Visit CFR website for more information.

CMAQ: Community Multiscale Air Quality is an active open-source development project of the U.S. EPA Atmospheric Science Modeling Division consisting of a suite of programs for conducting air quality model simulations.  CMAQ modeling is used by many agencies as part of the State Implementation Plan demonstrations for ozone and fine particulate matter.

CO: Carbon Monoxide - One of the "Six Common Air Pollutants", also known as "Criteria Pollutants" and is regulated by the U.S. EPA.  Click here to learn more about "Criteria Pollutants".

CO2: Carbon Dioxide.

Criteria Pollutants: Also known as "Six Common Pollutants" which are known to threaten human health and welfare.  Criteria pollutants include "ozone, carbon monoxide, nitrogen dioxide, particulate matter, sulfur dioxide, and lead."  There are threshold concentrations called National Ambient Air Quality Standards (NAAQS) established for each of them.  Click here to learn more about "Criteria Pollutants".

CSA: Combined Statistical Area is a grouping of metropolitan or micropolitan statistical areas that are linked by commuting ties. (Source: U.S. Census Bureau)

CSN: Chemical Speciation Network is a collection of monitors that are designed to monitor chemical makeup of particulate matter (PM).



D

Datalogger: An electronic device used for measuring analog or digital signals from an instrument and records the results a storage device.

Dry Deposition: The process by which gases and particles are transferred to the surface as a result of random turbulent air motions.  See atmospheric deposition; compare wet deposition.


E

EGU: Electrical Generating Unit, commonly known as power plant.

Emission: Substance discharge into the atmosphere from both natural and anthropogenic (human-made).  Natural sources include: air-blown dust from deserts; methane emitted by the digestion of food from animals; smokes from forest fires; sulfur, chlorine, and particles from volcanic activities; Anthropogenic sources include: exhausts from motor vehicles; smoke plume consisting of NOx, SO2, CO, etc. from power plants, and fossil fuel consumptions; VOCs from paint, hair spay, aerosol spays, etc. 

Emission Inventory: A listing by source, of the amount of air pollutants discharged into the atmosphere from a given area for a specified time period.  Emission Inventory at the present time only includes anthropogenic (human-made) sources.  See National Emission Inventory (NEI).

EPA: U.S. Environmental Protection Agency.

Equivalent Method: See Federal Equivalent Method.


F

FEM: Federal Equivalent Method is a method of sampling and analyzing for air pollution which has been accepted by EPA Administrator to be an acceptable alternative to normally used reference methods.

Fine Particles: See PM2.5.

FID: Flame Ionization Detector is a method typically used in analyzing compounds from a gas chromatography column.  (Source: Journal of Chromatographic Science)

FRM: Federal Reference Method is a method of sampling and analyzing for air pollution which has been accepted by EPA Administrator to be official as described in Title 40, Code of Federal Regulations, Part 50 (40 CFR Part 50).


G

GC: Gas Chromatography or gas-liquid chromatography - "the most commonly used procedure in contemporary chemical analysis."  (Source: Journal of Chromatographic Science) 


H

HAP: Hazardous Air Pollutants are airborne chemicals that cause serious health and environmental effects.  HAP are not covered in the National Ambient Air Quality Standards and they include: asbestos, beryllium, mercury, benzene, coke oven emissions, radionuclides, and vinyl chloride.

Haze: Atmospheric aerosols and particles that can degrade visibility and air quality.


I

IC: Ion Chromatography is a method of separating ions and polar molecules based on their charge properties.  The ions are usually detected by their conductivity.

IMPROVE: Interagency Monitoring of Protected Visual Environments is "a cooperative measurement effort governed by a steering committee composed of representatives from Federal and regional-state organizations.  The IMPROVE monitoring program was established in 1985 to aid the creation of Federal and State implementation plans for the protection of visibility in Class I areas (156 national parks and wilderness areas) as stipulated in the 1977 amendments to the Clean Air Act.  (Source: EPA/NPS IMPROVE Program)

IR: Infrared (radiation) is "[a type of] electromagnetic radiation [with] a wavelength longer than that of visible light, but shorter than that of microwaves." (Source: Wikipedia)


J

None


K

None


L

LADCO: Lake Michigan Air Directors Consortium is a regional air pollution planning organization representing the states of Illinois, Indiana, Michigan, and Wisconsin.


M

MANE-VU: Mid-Atlantic/Northeast Visibility Union is one of the five organizations consisting of tribal, local, state, federal air pollution agencies, and other interested parties.  The goal of an RPO is to work collaboratively in developing regional strategies to solve air pollution, addressing regional haze, and related issues.  MANE-VU includes states and tribal areas of Connecticut, Delaware, the District of Columbia, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, Northern Virginia, and suburbs of Washington, D.C.  Other RPOs include: CENRAP, Midwest RPO, VISTAS, and WRAP.  See each listed RPO to learn more or visit EPA website on RPO for a regional map and links.

MARAMA: Mid-Atlantic Regional Air Management Association, Inc. is a voluntary, non-profit association of ten state and local air pollution control agencies.  Memberships for MARAMA includes: Delaware, the District of Columbia, Maryland, New Jersey, North Carolina, Pennsylvania, Virginia, West Virginia, Philadelphia, and Allegheny County, PA.

MDE: Maryland Department of the Environment.

MDN: Mercury Deposition Network is an expansion of the National Atmospheric Deposition Program (NADP) in 1995.  It consists of more than 90 sites collecting weekly samples of precipitation and are analyzed by Frontier Geosciences for total mercury.

m/g3: Milligram per cubic meter of air - one of many units for expressing concentrations.

Midwest RPO: Midwest Regional Planning Organization is one of the five organizations consisting of tribal, local, state, federal air pollution agencies, and other interested parties.  The goal of an RPO is to work collaboratively in developing regional strategies to solve air pollution, addressing regional haze, and related issues.  Midwest RPO is an affiliation of Lake Michigan Air Director Consortium (LADCO) and includes states and tribal areas of Illinois, Indiana, Michigan, Ohio, and Wisconsin.  Other RPOs include: CENRAP, MANE-VU, VISTAS, and WRAP.  See each listed RPO to learn more or visit EPA website on RPO for a regional map and links.

MSA: Metropolitan Statistical Area is a "geographic entity defined by the U.S. Office of Management and Budget (OMB) for use by federal statistical agencies in collecting, tabulating, and publishing Federal statistics." An MSA consists of a core urban area of at least 50,000 people.  (Source: U.S. Census Bureau)


N

NAA: Non-Attainment Area is a geographic extent consisting of one or more counties where air pollution levels persistently exceed the National Ambient Air Quality Standards (NAAQS).

NAAQS: National Ambient Air Quality Standards are maximum threshold concentrations above which adverse health effects may occur.  EPA established NAAQS for Criteria Pollutants based on the 1970 Clean Air Act.

NACAA: National Association of Clean Air Agencies (formerly STAPPA and ALAPCO) is a national association representing air pollution control agencies in 53 states and territories and over 165 major metropolitan areas across the United States.

NADP/NTN: National Atmospheric Deposition Program/National Trends Network is a nationwide network to collect data on the chemistry of precipitation for monitoring of geographic and temporal long-term trends.  It currently consists of over 250 sites spanning the continental United States, Alaska, Puerto Rico, and the Virgin Islands.  Precipitation collected in the NADP/NTN network is analyzed for hydrogen (acidity as pH), sulfate, nitrate, ammonium, chloride, and base cations (such as calcium, magnesium, potassium, and sodium).

NCore: National Core multi-pollutant monitoring stations are a collection of monitors that integrates several advanced measurement systems for particles, pollutant gases and meteorology.

NEI: National Emission Inventory is an EPA database of air emissions information with input from numerous state and local air agencies, from tribes, and from industry.

Nephelometer: An instrument used to measure the light scattering component of light extinction.  It's an in-direct way of measuring visibility.

nm: Nanometer is an SI unit for measuring length. 1 nm equals 10-9 meter.

NO: Nitrogen Oxide.

NO2: Nitrogen Dioxide (ozone precursor).

NOx: Oxides of Nitrogen (ozone precursor).

NOy: Total Reactive Nitrogen Species (Ozone Precursor).


O

OAQPS: U.S. EPA's Office of Air Quality Planning and Standards.

O3: Ozone - One of the "Six Common Air Pollutants", also known as "Criteria Pollutants" and is regulated by the U.S. EPA.  Click here to learn more about Criteria Pollutants.

OTC: Ozone Transport Commission is a multi-state organization created under the Clean Air Act (CAA) to advise EPA on transport issues and develop regional control strategies to solve the ground-level ozone problem in the Northeast and the Mid-Atlantic.  OTC members consist of Connecticut, Delaware, the District of Columbia, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, and Virginia.


P

PAMS: Photochemical Assessment Network is a collection of monitors designed to measure ozone precursors (approximately 60 volatile hydrocarbons and carbonyl) as required by the 1990 Amendments to the Clean Air Act.  Each ozone non-attainment area designated as serious, severe, or extreme is required to operate from two to five stations depending on the population of a given area.  (Source: EPA Ambient Air Monitoring Program)

Pb: Lead.

PM: Particulate Matter - One of the "Six Common Air Pollutants", also known as "Criteria Pollutants" and is regulated by the U.S. EPA.  Click here to learn more about Criteria Pollutants.

PM10: Particulate Matter with an equivalent diameter less than or equal to 10μm.

PM2.5: Particulate Matter with an equivalent diameter less than or equal to 2.5μm.

ppb: Parts per billion (1 in 109) - one of many units for expressing concentrations.

ppm: Parts per million (1 in 106) - one of many units for expressing concentrations.


Q

QA: Quality Assurance is a rigorous process undertaken to ensure the quality of the data collected by a system or instrument.  QA procedures are deployed as part of the data collection process.

QC: Quality Control a rigorous process undertaken to maintain a specified level of data quality.  QC procedures are deployed after data have been collected (or after QA procedures).


R

Regional Haze: A cloud of aerosols and pollution extending up to hundreds of kilometers across a region and can degrade visibility and air quality.  To learn more about Regional Haze Rule and Program, click here.

RPO: Regional Planning Organization consists of tribal, local, state, federal air pollution agencies, and other interested parties.  The goal of an RPO is to work collaboratively in developing regional strategies to solve air pollution, addressing regional haze, and related issues.  There are five RPO: CENRAP, MANE-VU, Midwest RPO, VISTAS, and WRAP.  See each listed RPO to learn more or visit EPA website on RPO for a regional map and links.


S

SAAMP: State Ambient Air Monitoring Plans is a periodic assessment of the monitoring networks as required by regulations passed in 2006 under 40 CFR 58.10.  Visit EPA's SAAMP website for more information.

SIP: State Implementation Plan is a collection of rules, technical documentation, agreements, and strategies designed to attain and maintain the National Ambient Air Quality Standards (NAAQS) required by the 1970 Clean Air Act, and to prevent significant deterioration of air quality in areas cleaner than the standards.  To learn more about Maryland SIPs, click here.

SLAMS: State or Local Air Monitoring Stations is "a network of air monitoring stations for criteria pollutants using criteria set by the EPA's Office of Air Quality Planning and Standards (OAQPS) for their location and operation."  (Source: EPA Ambient Air Monitoring Program)

Smog: A mixture of air pollutants, smoke, dust, aerosols, etc. that can degrade air quality and visibility.  Smog was traditionally used to refer to ground-level ozone in an urban pollution plume.

SO2: Sulfur Dioxide - One of the "Six Common Air Pollutants", also known as "Criteria Pollutants" and is regulated by the U.S. EPA.  Click here to learn more about Criteria Pollutants.

STAPPA/ALAPCO: State and Territorial Air Pollution Program Administrators/Association of Local Air Pollution Control Agencies.  See National Association of Clean Air Agencies (NACAA).

STN: Speciation Trend Network.  See Chemical Speciation Network (CSN).


T

TEOM: Tapered Element Oscillating Microbalance is an instrument that measures continuous (hourly or sub-hourly) particulate matter mass.

Toxic Air Pollutants: See hazardous air pollutants (HAP).


U

μg/m3: Microgram per cubic meter of air - one of many units for expressing concentrations.

μm: Micrometer is an SI unit for measuring length.  1 μm equals 10-6 meter.

U.S. EPA: United States Environmental Protection Agency.

UV: Ultraviolet is "[a type of] electromagnetic radiation with a wavelength shorter than that of visible light, but longer than short X-rays."  (Source: Wikipedia)


V

Visibility: A measure of distance at which an object or light can be discerned.

VISTAS: Visibility Improvement State and Tribal Association of the Southeast is one of the five organizations consisting of tribal, local, state, federal air pollution agencies, and other interested parties.  The goal of an RPO is to work collaboratively in developing regional strategies to solve air pollution, addressing regional haze, and related issues.  VISTA includes states and tribal areas of Alabama, Florida, Georgia, Kentucky, Mississippi, North Carolina, South Carolina, Tennessee, Virginia, West Virginia, and the Eastern Band of the Cherokee Indians.  Other RPOs include: CENRAP, MANE-VU, Midwest RPO, and WRAP.  See each listed RPO to learn more or visit EPA website on RPO for a regional map and links.

VOCs: Volatile Organic Compounds are organic chemical compounds whose composition allow for them to evaporate under normal indoor atmospheric conditions of temperature and pressure. (Source: EPA)


W

Washout: The process by which gases and particles are removed from the atmosphere through rain.

Wet Deposition: The process by which gases and particles are transferred to the surface through incorporation with precipitation (rain, snow, mist, etc.).  See atmospheric deposition; compare dry deposition.

WRAP: Western Regional Air Partnership is one of the five organizations consisting of tribal, local, state, federal air pollution agencies, and other interested parties.  The goal of an RPO is to work collaboratively in developing regional strategies to solve air pollution, addressing regional haze, and related issues.  WRAP is the successor organization of the Grand Canyon Visibility Transport Commission.  Other RPOs include: CENRAP, MANE-VU, Midwest RPO, and VISTAS.  See each listed RPO to learn more or visit EPA website on RPO for a regional map and links.


XYZ

XRF: X-Ray Fluorescence is "the process of emissions of characteristic x-rays."  The analysis using x-ray fluorescence is called [X-ray Fluorescence Spectroscopy]."  This method is used to analyze chemical speciation of particles.  (Source: Amptek)


Additional Resources

EPA AirData

EPA AirNow

EPA Green Book

EPA Region 3 Radiation Information

EPA Terms of Environment: Glossary, Abbreviations and Acronyms

Sam Houston State University: Atmospheric Chemistry Glossary

VIEWS: Air Quality Glossary