Glossary

Acid Deposition

A comprehensive term for the various ways acidic compounds precipitate from the atmosphere and deposit onto surfaces. It can include 1) wet deposition by means of acid rain, fog and snow and 2) dry deposition of acidic particles (aerosols).

Acid Rain

Rain that is especially acidic (pH<5.2). Principal components of acid rain typically include nitric and sulfuric acid. These may be formed by the combination of nitrogen and sulfur oxides with water vapor in the atmosphere.

Acute Health Effect

An adverse health effect that occurs over a relatively short period of time (e.g. minutes or hours).

Add-On Control Device

An air pollution control device, such as a carbon absorber or incinerator, that reduces the pollution in exhaust gas. The control device usually does not affect the process being controlled and thus is "add-on" technology, as opposed to a scheme to control pollution through altering the basic process itself.

Adsorber

An emission control device that removes VOCs from a gas stream as a result of the gas attaching (adsorbing) onto a solid matrix, such as activated carbon.

Afterburner

An air pollution abatement device that removes undesirable organic gases through incineration.

Air

So-called 'pure' air is a mixture of gases containing about 78 percent nitrogen; 21 percent oxygen; less than one percent carbon dioxide, argon and other gases; and varying amounts of water vapor.

Air Basin

A land area with generally similar meteorological and geographic conditions throughout. To extend, possible boundaries are defined along political boundary lines and include both the source and receptor areas. California is currently divided into 15 air basins.

Air Pollutants

Amounts of foreign and/or natural substances occurring in the atmosphere that may result in adverse effects on humans, animals, vegetation and/or materials.

Air Quality Index (AQI)

A numerical index used for reporting severity of air pollution levels to the public. It replaces the formerly used Pollutant Standards Index (PSI). Like the PSI, the AQI incorporates five criteria pollutants - ozone, particulate matter, carbon monoxide, sulfur dioxide and nitrogen dioxide - into a single index. The new index also incorporates the eight-hour ozone standard and the 24-hour PM2.5 standard into the index calculation. AQI levels range from 0 (good air quality) to 500 (hazardous air quality). As a result, higher the index, higher the level of pollutants and greater the likelihood of health effects. The AQI incorporates an additional index category - unhealthy for sensitive groups - that ranges from 101 to 150. In addition, the AQI comes with more detailed cautions.

Air Quality Standard (AQS)

The prescribed level of a pollutant in the outside air that should not be exceeded during a specific time period to protect public health. It is established by both federal and state governments.

Air Toxics

A term referring to a harmful chemical or group of chemicals in the air. Substances that are especially harmful to health such as those considered under U.S. EPA's hazardous air pollutant program or California's AB 1807 and/or AB 2588 air toxics programs are considered to be air toxics. Technically, any compound that is in the air and has the potential to produce adverse health effects is defined as an air toxic.

Alternative Fuels

Fuels (e.g. methanol, ethanol, natural gas and liquid petroleum gas) that are cleaner burning and meet ARB's mobile and stationary emission standards. These fuels may be used in place of less clean fuels for powering motor vehicles.

Atmosphere

The mixture of gases surrounding the Earth. The Earth's atmosphere consists of about 79.1 percent nitrogen (by volume), 20.9 percent oxygen, 0.036 percent carbon dioxide and trace amounts of other gases. The atmosphere can be divided into a number of layers, according to its mixing or chemical characteristics, which are generally determined by temperature. The layer nearest the Earth is the troposphere, which reaches up to an altitude of about 8 km (about 5 miles) in the polar regions and up to 17 km (nearly 11 miles) above the equator. The stratosphere reaches to an altitude of about 50 km (31 miles) and lies above the troposphere. The mesosphere extends up to 80-90 km (about 50 to 56 miles) and is above the stratosphere. The thermosphere (or ionosphere) gradually diminishes and forms a fuzzy border with outer space. There is very little mixing of gases between layers.

Attainment Area

A geographic area, which is in compliance with the National and/or California Ambient Air Quality Standards (NAAQS OR CAAQS).

Attainment Plan

A plan that details the emission-reducing control measures and their implementation schedule necessary to attain air quality standards. In particular, the federal Clean Air Act requires attainment plans for non-attainment areas. These plans must meet several requirements including requirements related to enforceability and adoption deadlines.

Bay Area Air Quality Management District (BAAQMD)

BAAQMD is the regional government agency that regulates sources of air pollution within the nine San Francisco Bay Area Counties. The Air District's jurisdiction includes Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, southwestern Solano and southern Sonoma counties.

Best Available Control Technology (BACT)

BACT is the most up-to-date methods, systems, techniques and production processes available to achieve the greatest feasible emission reductions for given regulated pollutants and processes. BACT is a requirement of NSR (New Source Review) and PSD (Prevention of Significant Deterioration). BACT, as used in federal law under PSD, is defined as an emission limitation based on the maximum degree of emissions reductions allowable taking into account energy, environmental and economic impacts and other costs. [(CAA Section 169(3)]. BACT, as used in state law, means an emission limitation that will achieve the Lowest Achievable Emission Rates (LAER). This means it is the most demanding of either the most stringent emission limits contained in the SIP for the class or category of source (unless it is demonstrated that one limitation is not achievable) or the most stringent emission limit achieved in practice by that class or category of source. BACT, under state law, is more stringent than federal BACT and is equivalent to federal LAER, which applies to NSR permit actions.

Biological Contaminants

Agents derived from or are living organisms (e.g. viruses, bacteria, fungi and mammal and bird antigens) that can be inhaled and cause many types of health effects including allergic reactions, respiratory disorders, hypersensitivity diseases and infectious diseases. Also referred to as 'microbiologicals' or 'microbials.'

Building-Related Illness (BRI)

Diagnosable illness whose symptoms can be identified and its cause can be directly attributed to airborne building pollutants (e.g. Legionnaire's disease, hypersensitivity, and pneumonitis). Also, can be defined as a discrete identifiable disease or illness that can be traced to a specific pollutant or source within a building.

California Air Resources Board (ARB)

The State's lead air quality agency consisting of a nine-member Governor-appointed board. It is responsible for the attainment and maintenance of 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 Ambient Air Quality Standards (CAAQS)

Standards set by the State of California for the maximum levels of air pollutants that can exist in the outdoor air without unacceptable effects on human health or the public welfare. These are more stringent than NAAQS.

California Environmental Protection Agency (Cal/EPA)

The mission of Cal/EPA is to improve environmental quality, in order to protect public health, the welfare of our citizens and California's natural resources. Cal/EPA aims to achieve its mission in an equitable, efficient and cost-effective manner.

Carl Moyer Fund

A multi-million dollar incentive grant program designed to encourage the reduction of emissions from heavy-duty engines. The grants cover the additional cost of cleaner technologies for on-road, off-road, marine locomotive and agricultural pump engines, as well as, forklifts and airport ground support equipment.

Catalytic Converter

A motor vehicle pollution control device designed to reduce emissions, such as various nitrogen oxides, hydrocarbons, and carbon monoxide. Catalytic converters have been required equipment on all new motor vehicles sold in California since 1979.

Chemical Sensitization

Evidence suggests that some people may develop health problems characterized by effects, such as dizziness, eye and throat irritation, chest tightness and nasal congestion, which appear whenever they are exposed to certain chemicals. People may react to even trace amounts of chemicals to which they have become 'sensitized.'

Chronic Health Effect

An adverse health effect, which occurs over a relatively long period of time (e.g. months or years).

Clean Air Act Federal (CAA)

A federal law passed in 1970 and amended in 1977 and 1990, which forms the basis for the national air pollution control effort. Basic elements of the act include national ambient air quality standards for major air pollutants, air toxics standards, acid rain control measures and enforcement provisions.

Climate

The average weather (usually taken over a 30-year period) for a particular region and time period. Climate is not the same as weather but rather it is the average pattern of weather for a particular region. Weather describes the short-term state of the atmosphere. Climatic elements include precipitation, temperature humidity, sunshine, wind velocity phenomena (e.g. fog frost and hail storms) and other measures of weather.

Conformity

A demonstration of whether a federally-supported activity is consistent with the State Implementation Plan (SIP) - per Section 176 (c) of the Clean Air Act. Transportation conformity refers to the plans, programs and projects approved or funded by the Federal Highway Administration or the Federal Transit Administration. General conformity refers to the projects approved or funded by other federal agencies.

Diesel Engine

A type of internal combustion engine that uses low-volatility petroleum fuel and fuel injectors and initiates combustion using compression ignition (as opposed to spark ignition that is used with gasoline engines).

Electric Vehicle (EV)

A motor vehicle that uses an electric motor as the basis of its operation. EVs emit virtually no air pollutants.

Emission Inventory

An estimate of the amount of pollutants emitted into the atmosphere from mobile and stationary sources over a specific period of time (e.g. day or a year).

Emission Offset (also known as an emission trade-off)

A rule-making concept whereby approval of a new or modified stationary source of air pollution is conditional on the reduction of emissions from other existing stationary sources of air pollution. These reductions are required, in addition, to the reductions required by BACT.

Emission Standard

The maximum amount of a pollutant that is allowed to be discharged from a polluting source such as an automobile or smoke stack.

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 a disproportionate share of negative environmental and economic impacts resulting from the execution of environmental programs.

Ethanol

Ethyl-alcohol is a volatile alcohol containing two carbon groups (CH3CH2OH). For fuel use, ethanol is produced by fermentation of corn or other plant products.

Evaporative Emissions

Emissions from evaporating gasoline, which can occur during vehicle refueling, vehicle operation and even when the vehicle is parked. Evaporative emissions can account for two-thirds of the hydrocarbon emissions from gasoline-fueled vehicles on hot summer days.

Exceedence

A measured level of an air pollutant higher than the national or state ambient air quality standards.

Externality

Defined in economics, as the cost or benefit attributable to an economic activity that is not reflected in the price of the goods or services being produced. Thus, damage to the environment may not be counted as a cost (or environmental protection as a benefit) in production. In the aim of the "Polluter Pays Principle," polluters are required to meet the cost of avoiding pollution or remedying its effects to internalize the externalities.

Federal Implementation Plan (FIP)

In the absence of an approved State Implementation Plan (SIP), a plan prepared by the EPA provides measures that non-attainment areas are required to follow the Federal Clean Air Act.

Fuel Cell

An electrochemical cell which captures the electrical energy of the chemical reaction between fuels (e.g. liquid hydrogen and liquid oxygen) and converts it directly and continuously into the energy of a direct electrical current.

Global Warming

An increase in the temperature of the Earth's troposphere. Global warming has occurred in the past as a result of natural influences but the term is most often used to refer to the warming predicted by computer models to occur 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. Greenhouse gases allow incoming solar radiation to pass through the Earth's atmosphere but prevent most of the outgoing infrared radiation from the surface and lower atmosphere from escaping into outer space. This process occurs naturally and has kept the Earth's temperature about 60 degrees Fahrenheit warmer than it would otherwise be. Current life on Earth could not be sustained without the natural greenhouse effect. A number of scientists believe that the emission of CO₂ 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 oxides, ozone and water vapor, that slow the passage of re-radiated heat through the Earth's atmosphere by absorbing infrared radiation.

Hybrid Electric Vehicles (HEV)

HEVs operate using both electric and gasoline-powered motors. Emissions from HEVs are also substantially lower than conventional powered motor vehicles.

Hydrocarbons

Compounds containing various combinations of hydrogen and carbon atoms. They may be emitted into the air by natural sources (e.g. trees) and as a result of fossil and vegetative fuel combustion, fuel volatilization and solvent use. Hydrocarbons are a major contributor to smog.

Individual Cancer Risk (ICR)

The probability expressed as chances in a million that a person experiencing 70 years of continuous area-wide outdoor exposure to a toxic air contaminant will develop cancer.

Indoor Air Pollution

Air pollutants that occur within buildings or other enclosed spaces as opposed to those occurring in outdoor or ambient air. Examples of indoor air pollutants are nitrogen oxides, smoke, dust fibers, mists, bioaerosols, asbestos, formaldehyde and carbon monoxide.

Inert Gas

A gas that does not react with the substances coming in contact with it.

Inspection and Maintenance Program

A motor vehicle inspection program implemented by the California Bureau of Automotive Repair. The purpose of the program is to reduce emissions by assuring that cars are running properly. It is designed to identify vehicles in need of maintenance and to assure the effectiveness of their emission control systems on a biennial basis. Enacted in 1979 and strengthened in 1990. (Also known as the 'Smog Check' program).

Internal Combustion Engine

An engine in which both the heat energy and the ensuing mechanical energy are produced inside the engine. Examples of this are gas turbines, spark ignitions, gas and compression ignitions, and diesel engines.

Inversion Layer

A layer of warm air in the atmosphere that prevents the rise of cooling air and traps pollutants beneath it.

Lead

A gray-white metal that is soft, malleable, ductile and resistant to corrosion. Sources of lead, resulting in concentrations in the air, include industrial sources, crustal weathering of soils and fugitive dust emissions. Health effects from exposure to lead include brain and kidney damage and learning disabilities. Lead is the only substance which is currently listed as both a criteria air pollutant and a toxic air contaminant.

Mobile Sources

Sources of air pollution from automobiles, motorcycles, trucks, off-road vehicles, boats and airplanes.

Morbidity

Rate of disease incidence.

Multimedia Exposure

Exposure to a toxic substance from multiple pathways such as air, water, soil, food and breast milk.

National Ambient Air Quality Standards (NAAQS)

Standards set by the federal EPA for the maximum levels of air pollutants that can exist in the outdoor air without unacceptable effects on human health or the public welfare.

Nitrogen Oxides (Oxides of Nitrogen NOx)

A general term pertaining to compounds of nitric acid (NO), nitrogen dioxide (NO₂) and other oxides of nitrogen. Nitrogen oxides are typically created during combustion processes and are major contributors to smog formation and acid deposition. NO₂ is a criteria air pollutant and may result in numerous adverse health effects. NO₂ absorbs blue light resulting in a brownish-red cast to the atmosphere and reduced visibility.

Non-Attainment Area

A geographic area identified by the EPA and/or ARB as not meeting either NAAQS or CAAQS standards for a given pollutant.

Non-Point Sources

Diffuse pollution sources that are not recognized to have a single point of origin.

Office of Environmental Health Hazard Assessment (OEHHA)

The mission of OEHHA is to protect and enhance public health and the environment through objective scientific evaluation of risks posed by hazardous substances. While OEHHA does not promulgate environmental regulations directly, it is responsible for developing and providing risk managers in state and local government agencies with toxicological and medical information relevant to decisions involving public health.

Onboard Diagnostics

Devices incorporated into the computer systems of new motor vehicles to monitor components and systems that affect emissions when malfunctioning. If a problem is detected, the OBD system illuminates a warning lamp on the vehicle instrument panel to alert the driver. This warning lamp typically contains the phrase Check Engine or Service Engine Soon. The system also stores important information about the detected malfunction so that a repair technician can accurately find and fix the problem.

Onboard Vapor Recovery

Devices placed on vehicles to capture gasoline vapor during refueling and then route the vapors to the engine when the vehicle is started so that they can be efficiently burned.

Ozone

A strong smelling, pale blue, reactive toxic chemical gas consisting of three oxygen atoms. It is a product of the photochemical process involving the Sun's energy. Ozone exists in the upper atmosphere ozone layer as well as at the Earth's surface. Ozone at the Earth's surface causes numerous adverse health effects and is a criteria air pollutant. It is a major component of smog.

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 catalytically destroy ozone molecules in the stratosphere can cause a reduction in the ozone layer.

Ozone Layer

A layer of ozone in the lower portion of the stratosphere (12-15 miles above the Earth's surface) that helps to filter out harmful ultraviolet rays from the Sun. It can be contrasted with the harmful ozone component of photochemical smog near the Earth's surface.

Ozone Precursors

Chemicals, such as hydrocarbons and oxides of nitrogen, that occur either naturally or as a result of human activities and contribute to the formation of ozone - a major component of smog.

Particulate Matter (PM)

Solid or liquid particles of soot dust, smoke fumes, and aerosols.

Particulate Matter equal or less than 2.5 microns (PM2.5)

Ultra-fine particles or PM2.5 pose an increased health risk compared to PM10 because PM2.5 can deposit deep in the lung and contain substances that are particularly harmful to human health. The EPA promulgated national PM2.5 standards in 1997.

Particulate Matter less than 10 microns (PM10)

A major air pollutant consisting of tiny solid or liquid particles of soot dust, smoke fumes and aerosols. The size of the particles (10 microns or smaller - about 0.0004 inches or less) allows them to easily enter the air sacs in the lungs where they may be deposited and result in adverse health effects. PM10 also causes visibility reduction and is a criteria air pollutant.

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.

Point Sources

Specific points of origin where pollutants are emitted into the atmosphere such as factory smokestacks.

Pollution Prevention

The use of materials, processes or practices to reduce minimize or eliminate the creation of pollutants or wastes. It includes practices that reduce the use of toxic or hazardous materials, energy, water and/or other resources.

Prevention of Significant Deterioration (PSD)

A program used in the development of permits for new or modified industrial facilities in an area that is already in attainment. The intent of PSD is to prevent an attainment area from becoming a non-attainment area. The program, like NSR, can require BACT and if an AAQS is projected to be exceeded, Emission Offsets.

Proposition 65

Also known as the Safe Drinking and Toxic Enforcement Act of 1986. The Act is codified in the California Health and Safety Code Section 25249.5 et seq. It states that no person in the course of doing business shall knowingly discharge or release a chemical known to the state to cause cancer or reproductive toxicity into water or into land where such chemical passes or probably will pass into any source of drinking water without first giving clear and reasonable warning to such individual.

Radon (Rn) (and Radon Decay Products)

Radon is a radioactive gas formed in the decay of uranium. The radon decay products (also called radon daughters or progency) can be breathed into the lung where they continue to release radiation as they further decay.

Reactive Organic Gas (ROG)

A photochemically reactive chemical gas composed of non-methane hydrocarbons that may contribute to the formation of smog. Also, sometimes referred to as Non-Methane Organic Gases (NMOGs).

SCAQMD (South Coast Air Quality Management District)

The air pollution control agency for the four-county region including Los Angeles and Orange counties and parts of Riverside and San Bernardino counties. This area of 12000 square miles is home to more than 14 million people, which is about half the population of the State of California. It is the second most populous urban area in the United States. Because this area's smog problem is so severe, SCAQMD often finds itself at the forefront of the nation's efforts to reduce air pollution. SCAQMD, by law, is required to achieve and maintain healthful air quality for its residents. This is accomplished through a comprehensive program of planning, regulation, compliance, assistance, enforcement, monitoring, technology advancement and public education.

Scrubber

An air pollution control device that uses a high energy liquid spray to remove aerosol and gaseous pollutants from an air stream. The gases are removed either by absorption or chemical reaction.

Secondary Particle

Particles that are formed in the atmosphere. Secondary particles are products of the chemical reaction between gases, such as nitrates sulfur oxides, ammonia and organic products.

Smog

A combination of smoke and other particulates, ozone, hydrocarbons, nitrogen oxides and other chemically reactive compounds which under certain conditions of weather and sunlight may result in a murky brown haze that causes adverse health effects. The primary source of smog in California is motor vehicles. A major portion of smog comes from the burning of petroleum-based fuels such as gasoline. Other smog-formers include VOCs, which are found in products such as paints and solvents. Smog can harm health, damage the environment and cause poor visibility. Major smog occurrences are often linked to heavy motor vehicle traffic, sunshine, high temperatures and calm winds or temperature inversion (a weather condition in which warm air is trapped close to the ground instead of rising). Smog is often worse away from the source of the smog-forming chemicals since the chemical reactions that result in smog occur in the sky while the reacting chemicals are being blown away from their sources by winds.

Smog Check Program

(See Inspection and Maintenance Program).

SO2 (Sulfur Dioxide)

A strong smelling, colorless gas that is formed by the combustion 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 pollutant.

Soot

Very fine carbon particles that have a black appearance when emitted into the air.

State Implementation Plan (SIP)

A document, prepared by each state, describing existing air quality conditions and measures, which will be taken to attain and maintain national ambient air quality standards (see AQMP).

Stationary Sources

Non-mobile sources, such as power plants, refineries and manufacturing facilities, which emit air pollutants.

Toxic Air Contaminant (TAC)

TACs are substances identified in state regulations by the ARB. In 1993, the ARB expanded the TAC list to almost 200 substances and to include the hazardous air pollutants identified in the federal Clean Air Act Amendments (1990). The additional substances will be evaluated for potential health effects and prioritized for control measure development.

Toxic Hot Spot

A location where emissions from specific sources may expose individuals and population groups to elevated risks of adverse health effects, which iinclude but are not limited to cancer. These areas also contribute to the cumulative health risks of emissions from other sources nearby.

Transportation Control Measure (TCM)

Any control measure to reduce vehicle trips, vehicle use, vehicle miles traveled, vehicle idling or traffic congestion for the purpose of reducing motor vehicle emissions. TCMs can include encouraging the use of carpools and mass transit.

United States Environmental Protection Agency (EPA)

The federal agency charged with setting policies/guidelines and carrying out legal mandates for the protection of national interests in environmental resources.

Vehicle Miles Traveled (VMT)

The miles traveled by motor vehicles over a specified length of time (e.g. daily, monthly, or yearly) or over a specified road or transportation corridor.

Visibility

The distance that atmospheric conditions allow a person to see at a given time and location. Visibility reduction from air pollution is often due to the presence of sulfur and nitrogen oxides, as well as, particulate matter.

Volatile

Any substance that evaporates readily.

Volatile Organic Compounds (VOCs)

Hydrocarbon compounds that exist in the ambient air. VOCs contribute to the formation of smog and/or may themselves be toxic. VOCs often have an odor. Some examples include gasoline, alcohol and the solvents used in paints.

Zero-Emission Vehicle (ZEV)

Vehicles that produce no emissions from their on-board source of power (e.g. an electric vehicle). Under California's ZEV program, auto manufacturers are required, beginning in 2003, to produce a modest percentage of ZEVs. The ZEV program is promoting the development of battery-electric hybrid and fuel cell cars.