Glossary: Acronyms & Definitions
Air Toxics
Also known as toxic air pollutants or hazardous air pollutants, these are chemicals that cause or may cause serious effects in humans, and may be emitted into the air in quantities that are large enough to cause adverse health effects. These effects cover a wide range of conditions from lung irritation to birth defects to cancer. Health concerns may be associated with both short and long term exposures to these pollutants. Many are known to have respiratory, neurological, immune or reproductive effects, particularly for more susceptible sensitive populations such as children. 188 air toxics are listed as “Hazardous Air Pollutants” in the 1990 Clean Air Act.
AirToxScreen
USEPA’s Air Toxics Screening Assessment is an annual review and screening tool to address air toxics in the United States. The results of AirToxScreen are used by state, local, and tribal air quality agencies to identify which air toxics are impacting their region. This analysis of outdoor air quality enables agencies to identify emission sources and potential risks to public health caused by air toxics.
Background Concentrations
The pollutant levels that are found throughout the continental United States even in areas where no man-made air toxic emissions would be expected. They are a result of past emissions of persistent pollutants, long-range transport of recent emissions, widespread man-made sources, and also occur naturally.
Biogenic Emissions
A source category included in USEPA’s AirToxScreen, biogenic emissions are released through natural processes from plants, soils, and environmental events. AirToxScreen analyzes air toxics released from vegetation and soil, but does not include volcanic emissions, sea salt, and lightning, which are also biogenic sources. Biogenic emissions primarily consist of volatile organic compounds (VOCs) and oxides of nitrogen (NOx).
Carcinogen
A chemical that has been shown to cause cancer, either in people or animals.
CEP
USEPA’s Cumulative Exposure Project for 1990.
Chronic
Long duration or frequent recurrence.
Emissions Inventory
A list of activity categories that emit pollutants and an estimate of how much is emitted by each.
Exposure
Contact with a substance through inhalation, ingestion or some other means for a specific period of time.
Fire
An emission source category in USEPA’s AirToxScreen, fire includes wildfires, prescribed fires, and agricultural burns. Prescribed fires are controlled and conducted for a specific purpose, such as habitat restoration or to prevent future wildfires. They are performed in New Jersey by NJDEP Forest Fire Service. Agricultural burns are performed to control infested plant life and for other agricultural land upkeep. Agricultural fires require a permit and are only allowed in municipalities that do not ban open burning.
HAP
Hazardous air pollutant. In general, an “air toxic.” Specifically, this also refers to one of the 188 specific pollutants listed in the 1990 Clean Air Act amendments.
Health Benchmark
The chemical-specific air concentration below which there should be no significant harm to human health. For a carcinogen (cancer-causing chemical), the health benchmark is set at the air concentration that over a lifetime would cause no more than a one in a million increase in the likelihood of getting cancer. For a noncarcinogen, the health benchmark is the air concentration which is likely to cause no harm, even if exposure occurs on a daily basis for a lifetime.
MACT
Maximum Achievable Control Technology.
Major Sources
Defined in the Clean Air Act as a facility that emits at least 10 tons per year of one HAP, or 25 tons per year of a combination of HAPs. See also point source.
Mobile Sources
A source of air pollution which can move from place to place. In AirToxScreen, mobile sources are separated into on-road sources (cars, trucks, buses, motorcycles) and nonroad sources (airplanes, trains, construction equipment, lawnmowers, boats, dirt bikes, etc.).
NATA
National-scale Air Toxics Assessment. A screening tool developed by USEPA to estimate exposure to air toxics nationwide. Based on the National Emissions Inventory, NATA uses dispersion modeling to estimate ambient air concentrations and resulting risk to the population nationwide. NATA was released every three years from 1996-2014. In 2017, NATA became AirToxScreen, an annual release that includes an interactive mapping tool.
NEI
USEPA’s National Emissions Inventory is a database of nationwide air emissions data containing information on both criteria pollutants and hazardous air pollutants (HAPs) as well as the sources that emit them. The National Emissions Inventory informs the annual AirToxScreen with pollutant and source data from across the United States.
NJDEP
New Jersey Department of Environmental Protection
Noncarcinogen
A pollutant that can cause adverse health effects other than cancer.
Nonpoint/Area Sources
Small sources of air pollution which by themselves may not emit very much, but when their emissions are added together they may account for a sizable portion of the total emissions of air toxics. Nonpoint sources include small industrial sources that fall below the “major source” threshold. Included in this category are: consumer products (personal care products, household products, adhesives and sealants, automotive products, coatings), residential heating and fuel use, pesticide use, gasoline stations, dry cleaners, chromium electroplating, surface coating of cans and paper, metal parts cleaning, metal recycling, small chemical manufacturing plants, and bakeries, among others.
Particulate matter (PM)
Small particles suspended in the air that are respiratory irritants. There are two types of particulate matter regulated by USEPA and NJDEP. PM10 consists of inhalable particles while PM2.5 consists of fine inhalable particles. Although PM is a criteria pollutant and therefore not an air toxic, it can be made up of a broad range of chemicals, some of which are air toxics or precursors to air toxics.
Point Sources
A stationary facility that emits a significant amount of air pollution during manufacturing, power generation, heating, incineration, or other such activity. In AirToxScreen, USEPA includes large stationary sources as well as smaller sources submitted by state, local, and tribal air agencies. Because of this, some sources like crematoria, dry cleaners, and gas stations may be a point source in one state and a nonpoint source in another.
Pollutants
Unwanted chemicals or other materials found in the air. Pollutants can harm health, the environment and property. Many air pollutants occur as gases or vapors, but some are very tiny solid particles: dust, smoke or soot.
Reference Concentration
(RfC) – An estimate (with uncertainty spanning about an order of magnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of harmful effects during a lifetime. It can be derived from various types of human or animal data, with uncertainty factors generally applied to reflect limitations of the data used.
Risk Ratio
The comparison of the measured or estimated air concentration of a specific chemical to its health benchmark to determine either the magnitude of the risk of developing cancer or of some noncancer health effect. If the risk ratio for a chemical is less than one, the air concentration does not pose a health risk. If it is greater than one, it may be of concern. The risk ratio shows just how much higher the air concentration is than the health benchmark.
Secondary Formation
Also called atmospheric transformation, secondary formation occurs when pollutants are formed in the air through chemical reactions. When this happens, the original pollutant is replaced by one or more new chemicals, and can be more, less, or equally toxic to its precursors.
TRI
Toxic Release Inventory. This is a database of information about releases of more than 650 toxic chemicals from manufacturing facilities throughout the United States.
Unit Risk Factor
The upper-bound excess lifetime cancer risk estimated to result from continuous exposure to a chemical at a concentration of 1 µg/m3 in air. For example, if the Unit Risk Factor = 2 x 10-6 /µg/m3, then a person exposed daily for a lifetime to 1 µg of the chemical in 1 cubic meter of air would have an increased risk of cancer equal to 2 in a million.
Volatile Organic Compounds (VOCs)
Organic chemicals all contain the element carbon(C); organic chemicals are the basic chemicals found in living things and in products derived from living things, such as coal, petroleum and refined petroleum products. Many of the organic chemicals we use do not occur in nature, but were synthesized by chemists in laboratories. Volatile chemicals produce vapors readily; at room temperature and normal atmospheric pressure, vapors escape easily from volatile liquid chemicals. Volatile Organic chemicals include gasoline, industrial chemicals such as benzene, solvents such as toluene and xylene, and tetrachloroethylene (perchloroethylene, the principal dry cleaning solvent). Many volatile organic chemicals are also hazardous air pollutants; for example, benzene causes cancer.