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Terminology Services

CMAQ Glossary

Long Name:

Community Multiscale Air Quality (CMAQ) Glossary

Description:

Glossary of terms to support the CMAQ model microsite.

Publishing Organization:

Office of Research and Development/Center Environmental Measurement and Modeling/Atmospheric and Environmental Systems Modeling Division

Last Update:

March 21, 2017

Program Site:

https://www.epa.gov/cmaq

Terms & Acronyms

	Term
	advection	Definition: The transfer of heat or matter by the flow of a fluid, especially horizontally in the atmosphere or the sea.
	aerobic	Definition: Aerobic respiration takes place in the presence of oxygen and produces a large amount of energy. Carbon dioxide and water are produced as the waste products.
	air parcel	Definition: An imaginary body of air.
	albedo	Definition: The proportion of the incident light or radiation that is reflected by a surface, like a forest, desert, city, or ocean. It can also refer to the light reflected by a cloud.
	ammonia	Definition: One of the most abundant nitrogen-containing compounds in the atmosphere. It is an irritant with a characteristic pungent odor, which is widely used in industry. It is used in fertilizers to serve as a source of nitrogen for plants. Acronym: NH₃
	anaerobic	Definition: Anaerobic respiration takes place without the use of oxygen and produces small amounts of energy. Alcohol or lactic acid or other compounds are produced as waste products depending on the kind of cells that are active.
	critical loads	Definition: A quantitative estimate of an exposure to one or more pollutants below which significant harmful effects on specified sensitive elements of the environment do not occur according to present knowledge.
	domains	Definition: The area in space or time period over which a prediction is made.
	downwelling	Definition: The downwelling movement of an air mass in the atmosphere.
	eddy	Definition: In the Earth's atmosphere, small turbulent eddies occur in the daytime when surface air is warmed by contact with the ground and then rises. On a larger scale, the huge high- and low-pressure centers that move over the Earth may be considered eddies because they go against the general circulation.
	evapotranspiration	Definition: The sum of evaporation and plant transpiration from the Earth's land and ocean surface to the atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and water bodies. Transpiration accounts for the movement of water within a plant and the subsequent loss of water as vapor through stomata in its leaves.
	first principles	Definition: The fundamental concepts or assumptions on which a theory, system, or method is based.
	graupel	Definition: Also called soft hail or snow pellets, is precipitation that forms when super cooled droplets of water are collected and freeze on falling snowflakes.
	harmonic means	Definition: A kind of average. To find the harmonic mean of a set of n numbers, add the reciprocals of the numbers in the set, divide the sum by n, then take the reciprocal of the result.
	heterogeneous reactions	Definition: Heterogeneous reactions occur between reactants in two or more phases (e.g., solid and gas, solid and liquid) or in with participation of an interface (e.g., on the surface of a solid catalyst).
	nitrogen oxide	Definition: A generic term for the nitrogen oxides that are most relevant for air pollution, namely nitric oxide (NO) and nitrogen dioxide (NO₂). These gases contribute to the formation of smog and acid rain, as well as tropospheric ozone. Acronym: NOₓ
	oxidation	Definition: In a chemical reaction, molecules that are oxidized lose electrons. The atmosphere is an oxidizing environment.
	O₃	Definition: While ozone in the stratosphere can help protect us from ultraviolet rays, ground-level ozone poses health risks. Ground-level ozone does not come from a single source, but is formed in the air through a complex series of reactions involving light and chemical precursors like Nitrogen Oxides (NOₓ) and Volatile Organic Compounds (VOCs). Human and naturally occurring processes contribute to Ozone concentrations via NOₓ and VOC emissions. Breathing ozone can trigger a variety of health problems, particularly for children, the elderly, and people with lung diseases such as asthma. Ground level ozone can also have harmful effects on sensitive vegetation and ecosystems.
	planetary boundary layer	Definition: The troposphere can be divided into two parts: a planetary boundary layer, PBL, extending upward from the surface to a height that ranges anywhere from 100 to 3000 m, and above it, the free atmosphere. The boundary layer is directly influenced by the presence of the Earth's surface, responding to such factors as frictional surface drag, solar heating, and evapotranspiration. Each of these factors generates turbulence of various-sized eddies. Acronym: PBL
	radicals	Definition: A radical molecule contains at least one unpaired electron. With few exceptions, these unpaired electrons make free radicals highly chemically reactive towards other substances or themselves.
	snow pellets	Definition: See definition for graupel.
	soft hail	Definition: See definition for graupel.
	species	Definition: An individual molecule or chemical compound.
	total maximum daily load	Definition: A regulatory term in the U.S. Clean Water Act, describing a value of the maximum amount of a pollutant that a body of water can receive while still meeting water quality standards. Alternatively, TMDL is an allocation of that water pollutant deemed acceptable to the subject receiving waters. TMDLs have been used extensively by the EPA and state environmental agencies in implementing the Clean Water Act by establishing maximum pollution limits for industrial wastewater dischargers. Acronym: TMDL
	troposphere	Definition: The lowest region of the atmosphere, extending from the earth's surface to a height of about 3.7–6.2 miles (6–10 km), which is the lower boundary of the stratosphere. Because more solar radiation hits the equator than the poles, the troposphere is tallest along the equator and gets shorter as one moves north or south.
	upwelling	Definition: The upward movement of an air mass in the atmosphere.
	volatile organic compounds	Definition: Organic chemicals that have a high vapor pressure (i.e. extremely low boiling point) at ordinary room temperature. VOCs include human-made and naturally occurring chemical compounds. Some VOCs are dangerous to human health or cause harm to the environment. Harmful VOCs typically are not acutely toxic, but continued exposure to them may have long-term health effects. Acronym: VOCs

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