Clean Air Guide -- Glossary

A Glossary of definitions for words commonly used in Air Quality Discussions.

A

Acceptable Daily Intake (ADI): The highest daily amount of a substance that may be consumed over a person's lifetime without harmful health effects.

Acid Rain: A general term used to describe acid falling to earth in rain, snow, frost, fog or mist. Acid rain is formed when sulfur dioxide and nitrogen oxides released into the air become acid through chemical reactions and then fall to earth.

Adverse Health Effect: A health effect from exposure to air contaminants that may range from relatively mild temporary conditions, such as eye or throat irritation, shortness of breath, or headaches to permanent and serious conditions, such as birth defects, cancer or damage to lungs, nerves, liver, heart, or other organs.

Air District: A governing body responsible for managing air quality on a regional or county basis. California is currently divided into 35 air districts.

Air Pollutants: High amounts of contaminants in the air that have harmful effects to humans, animals, vegetation, and/or materials.

Air Pollution: Worsening of air quality resulting from unwanted chemicals or other pollutants occurring in the air.

Air Quality Index (AQI): A scale developed by the government to measure how much air pollution is in the air. The AQI measures five criteria pollutants -- ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide. AQI levels range from 0 (Good air quality) to 500 (Hazardous air quality). The higher the index, the higher the level of pollutants and the greater the likelihood of health effects. The AQI also has another category -- unhealthy for sensitive groups -- that ranges from 101 to 150. The AQI is usually used in weather reports. When it is high, there are warnings for people not to do things like sports or hard work outside. People with asthma or other lung problems are urged to stay inside on days that the AQI is high.

Air Quality Management District (AQMD): A group of counties or parts of counties that regulate stationary, indirect, and area sources of air pollution within a region. It contains a regional air pollution control board that mostly includes elected officials from within the region.

Air Toxics: A general term referring any pollutant that is in the air and has the potential to produce harmful health effects is an air toxic.

Asthma: A chronic inflammatory ailment of the lungs characterized by wheezing, breathlessness, chest tightness, and cough.

C

California Air Resources Board (CARB): The State's lead air quality agency consisting of an eleven-member board appointed by the Governor and several hundred employees. CARB is responsible for attainment and maintenance of the state and federal air quality standards, and is fully responsible for motor vehicle pollution control. It oversees county and regional air pollution management programs.

California Clean Air Act (CCAA): A California law passed in 1988 which provides the basis for air quality planning and regulation independent of federal regulations. A major element of the Act is the requirement that local air districts in violation of the CAAQS must prepare attainment plans which identify air quality problems, causes, trends, and actions to be taken to attain and maintain California's air quality standards by the earliest practicable date.

California Environmental Protection Agency (Cal/EPA): A state government agency established in 1991 for unifying environmental activities related to public health protection in the State of California. There are six boards, departments, and offices under Cal/EPA including the California Air Resources Board (ARB), California Integrated Waste Management Board (IWMB), State Water Resources Control Board (SWRCB) and its nine Regional Water Quality Control Boards (RWQCB), Department of Pesticide Regulation (DPR), Department of Toxic Substances Control (DTSC), and Office of Environmental Health Hazard Assessment (OEHHA). The Cal/EPA boards, departments, and offices are directly responsible for implementing California environmental laws, or play a cooperative role with other regulatory agencies at regional, local, state, and federal levels.

Carbon Dioxide (CO2): A colorless, odorless gas that occurs naturally in the Earth's atmosphere. Significant quantities are also emitted into the air by fossil fuel combustion.

Carbon Monoxide (CO): A colorless, odorless gas resulting from the incomplete combustion of fuels. CO interferes with the blood's ability to carry oxygen to the body's tissues and results in numerous harmful health effects. Over 80% of the CO emitted in urban areas is contributed by motor vehicles. CO is a criteria air pollutant.

Carcinogen: A cancer-causing substance.

Criteria Air Pollutant: Six common air pollutatns that are regulated under the state and federal Clean Air Acts. They include ozone, lead, nitrogen oxide, sulfur dioxide, carbon monoxide, and particulate matter.

E

Emissions: Substances released into the air, usually by human activities such as burning fossil fuels.

Emission Offsets (also known as Emissions Trading): A regulation that allows for a new or modified stationary source of air pollution only if there is a reduction of emissions from another already existing stationary source or sources of air pollution.

Environmental Justice: The fair treatment of people of all races and incomes with respect to development, implementation, and enforcement of environmental laws, regulations, and policies. Fair treatment implies that no person or group of people should shoulder an unfair share of negative environmental, health and economic impacts resulting from environmental programs.

F

Federal Clean Air Act (FCAA): A federal law passed in 1970 and amended in 1974, 1977 and 1990 which forms the basis for the national air pollution regulation. Basic elements of the act include national ambient air quality standards for major air pollutants, mobile and stationary control measures, air toxics standards, acid rain control measures, and enforcement provisions.

Fossil Fuels: Fuels such as coal, oil, and natural gas; so-called because they are the remains of ancient plant and animal life.

G

Global Warming: An increase in the temperature of the Earth's troposphere. Global warming is the term most often used to refer to the warming as a result of increased emissions of greenhouse gases.

Greenhouse Effect: The warming effect of the Earth's atmosphere. Light energy from the sun which passes through the Earth's atmosphere is absorbed by the Earth's surface and re-radiated into the atmosphere as heat energy. The heat energy is then trapped by the atmosphere, creating a situation similar to that which occurs in a car with its windows rolled up. The release of carbon dioxide and other gases into the atmosphere may increase the greenhouse effect and contribute to global warming.

Greenhouse Gases: Atmospheric gases such as carbon dioxide, methane, chlorofluorocarbons, nitrous oxide, ozone, and water vapor that slow the passage of re-radiated heat through the Earth's atmosphere.

H

Hazardous Air Pollutant (HAP): An air pollutant listed under section 112 (b) of the Federal Clean Air Act as very hazardous to health. Emission sources of hazardous air pollutants are identified by U.S. EPA, and emission standards are set accordingly.

Haze (Hazy): A phenomenon that results in reduced visibility due to the scattering of light caused by aerosols. Haze is caused in large part by human-made air pollutants.

I

Indirect Source: Any facility, building, structure, or installation, that causes increased mobile source pollution, such as car traffic. Examples of indirect sources include employment sites, shopping centers, sports facilities, housing developments, airports, commercial and industrial development, and parking lots and garages.

Indoor Air Pollution: Air pollutants that occur inside buildings or other enclosed spaces, Some examples of indoor air pollutants are nitrogen oxides, tobacco smoke, asbestos, formaldehyde, and carbon monoxide.

M

Major Source: A stationary facility that emits a regulated pollutant in an amount exceeding the threshold level depending on the location of the facility and attainment with regard to air quality status.

Mobile Sources: Sources of air pollution such as automobiles, motorcycles, trucks, off-road vehicles, boats, and airplanes.

N

National Ambient Air Quality Standards (NAAQS): Standards established by the United States EPA that apply for outdoor air throughout the country. There are two types of NAAQS. Primary standards set limits to protect public health and secondary standards set limits to protect public welfare.

Natural Sources: Non-humanmade emission sources, including biological and geological sources, wildfires, and windblown dust.

New Source Performance Standards (NSPS): Uniform national EPA air emission standards that limit the amount of pollution allowed from new sources or from modified existing sources.

New Source Review (NSR): A Clean Air Act requirement that State Implementation Plans must include a permit review, which applies to the construction and operation of new and modified stationary sources in nonattainment areas, to ensure acceptable levels of national ambient air quality standards. The two major requirements of NSR are Best Available Control Technology and Emission Offsets.

Nonattainment Area: A geographic area identified by the U.S. EPA and/or CARB as not meeting either NAAQS or CAAQS standards for a given pollutant.

O

Office of Environmental Health Hazard Assessment (OEHHA): A department within the California Environmental Protection Agency that is responsible for rating chemicals for harmful health impacts and establishing safe exposure levels. OEHHA also assists in performing health risk assessments and developing risk assessment procedures for air quality management purposes.

Ozone: A harmful form of oxygen that is produced when sunlight creates a reaction between nitrogen oxide and hydrocarbons. Next to the earth's surface, ozone is a major component of smog. Ozone exists in the upper atmosphere ozone layer (stratospheric ozone) as well as at the Earth's surface in the troposphere (ozone). Ozone in the troposphere causes numerous harmful health effects and is a criteria air pollutant.

Ozone Depletion: The reduction in the stratospheric ozone layer. Stratospheric ozone shields the Earth from ultraviolet radiation. The breakdown of certain chlorine and/or bromine-containing compounds that destroy ozone molecules in the stratosphere can cause a reduction in the ozone layer.

Ozone Precursors: Chemicals such as non-methane hydrocarbons and oxides of nitrogen, occurring either naturally or as a result of human activities, which contribute to the formation of ozone, a major component of smog.

P

Particulate Matter (PM): Any solid material, except pure water, that is suspended or carried in the air. The size of particulate matter can vary from coarse, wind-blown dust particles to fine particle combustion products.

Permit: Written authorization from a government agency (e.g., an air quality management district) that allows for the construction and/or operation of an emissions generating facility or its equipment within certain specified limits.

PM2.5: Includes tiny particles with an aerodynamic diameter less than or equal to a nominal 2.5 microns. This fraction of particulate matter penetrates most deeply into the lungs.

PM10 (Particulate Matter): A criteria air pollutant consisting of small particles less than 1/7 the width of a single human hair. Their small size allows them to make their way to the air sacs deep within the lungs where they cause harmful health effects. PM10 also causes visibility reduction.

Pollution Prevention: The use of materials, processes, or practices to reduce, minimize, or eliminate the creation of pollutants or wastes.

Public Workshop: A workshop held by a public agency for the purpose of informing the public and getting its input on the development of a regulatory action, or a development that may add to the air pollution levels.

R

Regional Haze: The haze produced by many different sources and activities that release fine particles across a large area.

S

Smog: A combination of smoke and other particulates, ozone, hydrocarbons, nitrogen oxides, and other chemically reactive compounds. Under certain weather conditions they may produce a murky brown haze that causes harmful health effects. The primary source of smog in California is motor vehicles.

Smoke: A form of air pollution made up mostly of particulate matter. Other components of smoke include gaseous air pollutants such as hydrocarbons, oxides of nitrogen, and carbon monoxide.

Soot: Very fine carbon particles that have a black appearance when released into the air.

Source: Any place or object from which air pollutants are released. Sources that are fixed in space are stationary sources and sources that move are mobile sources.

State Implementation Plan (SIP): A plan prepared by states and sent to U.S. EPA describing how each area will attain and maintain national ambient air quality standards.

Stationary Sources: Non-mobile sources such as power plants, refineries, and manufacturing facilities which release air pollutants.

Sulfur Dioxide (SO2): A strong smelling, colorless gas that is formed by the burning of fossil fuels. Power plants, which may use coal or oil high in sulfur content, can be major sources of SO2. SO2 and other sulfur oxides contribute to the problem of acid deposition. SO2 is a criteria air pollutant.

T

Toxic Air Contaminant (TAC): An air pollutant that may cause or contribute to an increase in deaths or in serious illness, or it may pose a present or potential hazard to human health.

Toxic Hot Spot: A location where emissions from specific sources may expose people to higher risks of harmful health effects -- including but not only cancer.

U

United States Environmental Protection Agency (U.S. EPA): The federal agency charged with setting policy and guidelines, and carrying out legal mandates for the protection of national interests in environmental resources.

V

Variance: Permission granted for a limited time (under stated conditions) for a person or company to operate outside the air pollution limits stated in a regulation.

Visibility: The ability to see and identify objects at different distances. Visibility reduction from air pollution is often due to the presence of sulfur and nitrogen oxides, as well as particulate matter.

Volatile Organic Compounds (VOCs): Carbon-containing compounds that evaporate into the air. VOCs contribute to the making of smog and may be toxic. VOCs often have an odor, and some examples include gasoline, alcohol, and the solvents used in paints.