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Improving Air Quality in Your Community


Information provided for informational purposes onlyNote: EPA no longer updates this information, but it may be useful as a reference or resource.


Disclaimer: This list of glossary terms was compiled from existing EPA definitions and supplemented, where necessary, by additional terms and definitions. The wording of selected items may have been modified from the original in order to help readers who are new to air pollution control activities to more readily comprehend the underlying concept of the glossary entry. As such, these glossary definitions constitute neither official EPA policy nor preempt or in any way replace any existing legal definition required by statute or regulation.


Affected (or Interested) Parties – Individuals and organizations potentially acted upon or affected by chemicals, radiation, or microbes in the environment or influenced favorably or adversely by proposed risk management actions and decisions.

Air Emissions – The release or discharge of a pollutant into the air.

Air Toxic – Any air pollutant that causes or may cause cancer, respiratory, cardiovascular, or developmental effects, reproductive dysfunctions, neurological disorders, heritable gene mutations, or other serious or irreversible chronic or acute health effects in humans. See hazardous air pollutant.

Aneroid blood pressure cuffs – non-liquid blood pressure cuffs.

Area Source – A stationary source that emits less than 10 tons per year of a single hazardous air pollutant (HAP) or 25 tons per year of all HAPs combined.

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Background Levels – The concentration of a chemical already present in an environmental medium due to sources other than those under study. Two types of background levels may exist for chemical substances: (a) Naturally occurring levels of substances present in the environment, and (b) Anthropogenic concentrations of substances present in the environment due to human associated activities (e.g., automobiles, industries).

Bath – a tank of chemicals in which a metal part is dipped to apply a metal coating.

Bath dumps – Chemicals that have degraded or become contaminated over time and no longer serve their function.

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Cancer – A group of related diseases characterized by group of diseases characterized by the uncontrolled growth of abnormal cells.

Carbon adsorbers – Control devices that remove vapors from an air stream by adsorbing the vapor onto an activated carbon surface.

Carcinogen(ic) – An agent capable of inducing cancer.

Community – The persons associated with an area who may be directly affected by area pollution because they currently live in or near the area, or have lived in or near the area in the past (i.e., current or past residents), members of local action groups, local officials, tribal governments, health professionals, and local media. Other entities, such as local industry, may also consider themselves part of the community.

Control Technology/Measures – Equipment, processes or actions used to reduce air pollution at the source.

Creosote – An oily residue that forms from unburned wood gases.

Criteria Air Pollutant – One of six common air pollutants determined to be hazardous to human health and regulated under EPA's National Ambient Air Quality Standards (NAAQS). The six criteria air pollutants are carbon monoxide, lead, nitrogen dioxide, ozone, sulfur dioxide, and particulate matter. The term "criteria pollutants" derives from the requirement that EPA must describe the characteristics and potential health and welfare effects of these pollutants. It is on the basis of these criteria that standards are set or revised.

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Densified logs – Logs that are made of compressed sawdust.

Diisocyanates – Chemicals in auto body part painting operations, especially for clear coat applications, which are a leading cause of occupational asthma.

Dry, seasoned wood – Wood that has been split and dried for at least six months and has <20% moisture by weight.

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Emission Rate – The amount of a given substance discharged to the air per unit time, expressed as a fixed ratio (e.g., tons/yr).

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Fine Particulate Matter – Particulate matter less 2.5 microns across or less.

Fountain solution – A plating solution that keeps the ink from adhering where it should not on the plate.

Fugitive Release – Emission of a chemical to the air that does not occur from a stack, vent, duct, pipe or other confined air stream (e.g., leaks from joints).

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Greenhouse Gas (GHG) – Any gas that absorbs infrared radiation in the atmosphere. Greenhouse gases include, but are not limited to, water vapor, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrochlorofluorocarbons (HCFCs), ozone (O3), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6).

Gun wash system – A cleaning system used to clean spray guns after being used to spray auto body parts.

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Hazardous Air Pollutants (HAP) – Defined under the Clean Air Act as pollutants that cause or may cause cancer or other serious health effects, such as reproductive effects or birth defects, or adverse environmental and ecological effects. Currently, the Clean Air Act regulates 188 chemicals and chemical categories as HAPs.

Heavy metals – Metals such as chromium, cadmium, mercury, and lead.

High solids paints and coatings – Paints and coatings with more solids and less solvents than conventional coatings.

High-Volume Low-Pressure (HVLP) spray guns – A spray gun that uses columns of low pressure air to cause turbulence within the paint as the first stage of atomization. The air used for the final step of atomization originates from high-volume turbine blowers and is transferred to the gun using large-diameter air lines.

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Incomplete Combustion – Fuel from the firewood that does not burn.

Indoor Source – Objects or places within buildings or other enclosed spaces that emit air pollutants.




Low emission vapor degreasers (LEVD) – Completely enclosed, airtight units used to clean off machining oil and other contaminants from metal parts.

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Metalizing – A process in which pure metal (not paint) is sprayed onto a ship’s surface.

Major Source – Under the Clean Air Act, a stationary source that emits more than 10 tons or more per year of a single hazardous air pollutant (HAP) or 25 or more tons per year of all HAPs.

Mobile Source Air Toxics – Air toxics that are emitted from non-stationary objects that release pollution. Mobile sources include cars, trucks, buses, planes, trains, motorcycles and gasoline-powered lawn mowers. Another example is a portable generator.

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Natural Source – Non-manmade emission sources, including biological (biogenic sources such as plants) and geological sources (such as volcanoes), and windblown dust.

Nonroad Mobile Sources – Sources such as farm and construction equipment, gasoline-powered lawn and garden equipment, and power boats and outdoor motors that emit pollutants.

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Off-Specification – Paint or coating material that does not meet quality or customer specifications.

Onroad Mobile Source – Any mobile source of air pollution such as cars, trucks, motorcycles, and buses that travels on roads and highways.

Overspray – The amount of spray that misses its target.

Ozone Depleting Substances (ODS) – Substances that cause the deterioration of the earth’s protective ozone layer.

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Particle Pollution – Fine liquid or solids such as dust, smoke, fumes, or smog found in air or emissions.

Particulates/Particulate Matter (PM) – Solid particles or liquid droplets suspended or carried in the air.

Pigment – Provides color to the paint or coating.

Plating – The process where the surface of the metal is modified by adding several layers of metal coating by using a series of baths and then allowing the part to dry.

PM-10/PM-2.5 – PM-10 or PM10 refers to particles in the atmosphere with a diameter of less than ten or equal to 10 micrometers. PM-2.5 or PM2.5 refers to smaller particles in the air (i.e., less than or equal to 2.5 micrometers in diameter).

Point Source – A stack, vent, duct, pipe or other confined air stream from which chemicals may be released to the air.

Pollution Prevention (P2) – Pollution prevention is the use of materials, processes, or practices that reduce or stop the creation of pollutants or waste at the source. It includes improved operating practices like material substitution, process and equipment modifications, and energy and wastewater conservation. Pollution prevention is stopping pollution before it starts.

Pyrometallurgical treatment – High temperature processing used in metal casting.

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Refrigerated condensers – Control devices that recover solvent vapor emissions by cooling the air stream to the point it condenses to liquid form.

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Sharps – Items such as needles or broken glass that may puncture the skin.

Solvent – A solvent is a liquid that is capable of dissolving another substance to make a new solution. Solvents are used to dissolve paint solids to make paint and as cleaning solutions because they dissolve grease and oils.

Solvent-based inks – Set by evaporation of the ink oil at elevated temperatures.

Source – Any place or object from which pollutants are released.

Source Category – A group of similar industrial processes or industries that are contributors to releases of hazardous air pollutants. The 1990 amendments to the Clean Air Act (CAA) requires that the EPA publish and regularly update a listing of all categories and subcategories of major and area sources that emit hazardous air pollutants.

Spill container – Catches and contains spilled solvent from the dry cleaning machine.

Stack – A chimney, smokestack, or vertical pipe that discharges used air.

Stakeholder(s) – Any organization, governmental entity, or individual that has a stake in or may be impacted by a given approach to environmental regulation, pollution prevention, energy conservation, etc.

Stationary Source – A source of pollution that is fixed in space.

Substrate – The material on which another material is coated or fabricated (substratum).

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Toxic Air Pollutants – see hazardous air pollutant.

Toxicity – The degree to which a substance or mixture of substances can harm humans or animals.

Transfer efficiency – The percentage of material atomized through the spray gun that actually ends up as a coating on the desired surface.

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UV-Cured Inks – Inks that are set by using radiant energy.

UV Light Cured Coatings – These coatings use UV light to set the coating instead of solvents.

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Vapor – The gas given off by substances that are solids or liquids at ordinary atmospheric pressure and temperatures.

Volatile Organic Compounds (VOC) – Organic compounds that vaporize (become a gas) at room temperature.  VOC are the leading cause of ground-level ozone (air pollution, also known as "smog").   Common sources which may emit VOC into the air include housekeeping and maintenance products; paints, coatings, and inks; and building and furnishing materials.  In sufficient quantities, VOC can cause eye, nose, and throat irritations, headaches, dizziness, visual disorders, memory impairment; some are known to cause cancer in animals; some are suspected of causing, or are known to cause, cancer in humans.

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Work practices – an action performed by workers to prevent or reduce emissions of air toxics. Such actions can include vacuuming up dust, opening containers only when necessary, and keeping employees updated on housekeeping measures.




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