Actual Emissions – the emissions produced by a facility or operation based on its normal operating conditions. This may be derived from actual measurements or emissions testing, or historical records of activities which can be used to estimate emissions.

Agricultural Source of Air Pollution – a source or a group of sources of air pollution created by or used in the production of crops, or the raising of fowl or animals located on contiguous property under common ownership or control. Under SB700, there are four categories of emissions: confined animal facilities; internal combustion engines (including portable and off-road engines); sources subject to Federal Title V requirements; and sources subject to local district regulation as allowed by the Health & Safety Code.

Air Pollution Control District (APCD)/Air Quality Management District (AQMD) – a governmental entity often aligned with county government with responsibilities for developing and administering air pollution control programs on a local or regional level. Some regional AQMD’s are specifically authorized in California statutes; other agencies not specifically identified may be unified among several adjacent counties to more effectively and efficiently administer the local air pollution programs within a common air basin. Every APCD and AQMD has a governing board.

Attainment/Nonattainment – (attainment) any area that meets the ambient air quality standards for a pollutant as determined by the Environmental Protection Agency (for national standards) and the California Air Resources Board (for state standards). Nonattainment is designated for any area that does not meet such standards.

Best Available Control Measures (BACM) – the application of methods and techniques to operations and activities not applicable for "best available control technology," which achieve the maximum degree of reduction of a pollutant subject to regulation, taking into account energy, environmental, economic impacts, and other costs, as applicable to the specific activity or operation. Examples of activities to which BACM apply include generation of fugitive dust; agricultural burning; dairy ammonia.

Best Available Control Technology (BACT) – the application of pollution controls, such as production processes, methods, techniques, and systems, which achieve the maximum degree of reduction of a pollutant subject to regulation, and which (1) takes into account energy, environmental, economic impacts, and other costs, as applicable to a facility or operation; or (2) has been achieved in practice at other similar sources. In no event can the application of such controls result in emissions which exceed specified emissions limits. Examples of processes to which BACT apply include internal combustion and fuel dispensing. BACT applies to new facilities or operations, and to major modifications of existing facilities or operations.

Best Available Retrofit Control Technology (BARCT) – similar to the definition of BACT, except that the pollution controls apply to the retrofitting of existing equipment.

California Air Pollution Control Officers Association (CAPCOA) – a non-profit association of the air pollution control officers from all 35 local air quality agencies throughout California.

California Air Resources Board (CARB) – the state agency with the responsibility of administering the air pollution control efforts throughout the state. This includes oversight of local air district programs and primary responsibility for the control of certain pollution sources, including mobile sources (not otherwise pre-empted by federal authority) and consumer products.

California Clean Air Act (CCAA)– California legislation signed into law in 1988 which delineates, in statutes, California’s air quality goals, planning mechanisms, regulatory strategies, and standards of progress. Among other things, the CCAA requires attainment of the State’s ambient air quality standards at the earliest practical date.

California Health & Safety Code – that portion of state law which contains the requirements for air pollution control activities in California. SB700, for example, is contained within the California Health & Safety Code.

Confined Animal Facilities (CAFs) – any type of confinement for animals or fowl that restricts them to a certain area, and involves feeding the animals by any method other than grazing. This includes, but not limited to, barns, pens, corrals, and coops.

Cost Effectiveness – the cost of a particular air pollution control or control measure expressed per unit of emissions reduced; for example, "$1,000 per ton of NOx reduced."

DeMinimis Emissions – a level of emissions below which is considered not to be significant or meaningful.

Emission Offsets – an amount of emissions required to be reduced from other facilities in order for a facility or operation to be granted increases in emissions as a result of federal New Source Review requirements. Generally, such offsets are gained via Emission Reduction Credits generated by other facilities.

Emission Reduction Credits (ERCs)– Emission reductions from a facility which are verified to be over and above the emissions reductions required by a federal, state, or district rule, and which are demonstrated to be real, permanent, quantifiable, enforceable, and surplus. ERCs can be "sold" to facilities or operations in need of emission offsets.

Environmental Protection Agency (USEPA) – the federal agency responsible for the oversight of programs to improve the environment. Simply stated, the USEPA has oversight authority over state and local air pollution control programs, assures timely progress toward attainment of national ambient air quality standards, promulgates regulations, has enforcement authority, and carries out the directives specified in the Federal Clean Air Act.

Federal Clean Air Act (FCAA)– the federal legislation which enables a multitude of programs and requirements to clean the air. The original FCAA was signed into law in 1963, but the key enabling provisions occurred with the reauthorization of the FCAA in 1970. Subsequent amendments have occurred in 1975, 1977, and most recently, 1990. The FCAA as amended in 1990 includes five key parts (or "Titles"): (1) Air Pollution Prevention and Control; (2) National Emissions Standards Act; (3) General Provisions; (4) Acid Deposition Control; and (5) Federal Permits.

Fugitive Emissions – those emissions that cannot reasonably pass through a stack, chimney, vent, or other functionally equivalent opening. Examples might include dust from tilling and harvesting; or ammonia from dairy manure piles.

Major Source – any stationary source or group of stationary sources within a contiguous area and under common control that emits or has the potential to emit, considering controls, in the aggregate, levels which exceed those specified by the severity of pollution in an attainment or nonattainment area; [Note: NOx, VOC, and PM10 major source thresholds are listed by county in Appendix C]; or which emits 10 tons or more per year of any hazardous air pollutant, or 25 tons per year or more of any combination of hazardous air pollutants.

Mitigation Clearinghouse – a listing of Best Available Control Technologies, Best Available Retrofit Control Technologies, Best Available Control Measures, and Reasonably Available Control Measures as applicable to agricultural sources, including operations that create fugitive dust (including, but not limited to, disking, tilling, material handling and storage, travel on unpaved roads); confined animal facilities; internal combustion engines used in agricultural operations; and other equipment, operations, or activities that emit, or cause to be emitted, any regulated air pollutant or pollutant precursor. This clearinghouse is under the responsibility of CAPCOA.

Modification – any physical change in, or change in the method of operation, of a stationary source which results in an increase in the amount of any pollutant emitted by such source or which results in the emission of any air pollutant not previously emitted.

National Ambient Air Quality Standards (NAAQS) – the definition of "clean air." More specifically, a standard establishes the concentration above which the pollutant is known to cause adverse health effects to sensitive groups within the population, such as children and the elderly, and allows for an adequate margin of safety. Health-based standards have been established for the "criteria pollutants," including ozone, PM10, PM2.5, nitrogen dioxide, carbon monoxide, sulfur dioxide, and lead.

New Source – any stationary source, the construction or modification of which commenced after the publication or adoption of regulations prescribing a standard of performance applicable to that specific source.

New Source Review (NSR) – a program to assure that new sources do not adversely contribute to an area’s ability to attain National Ambient Air Quality Standards. There are very strict federal requirements regarding this program.

Oxides of Nitrogen – a class of pollutants which are formed primarily through combustion processes. Some oxides of nitrogen are harmful to humans; others are not. These pollutants are precursors to the formation of two of the most harmful pollutants: ozone and fine particulate matter.

Ozone – a pollutant, comprised of three oxygen atoms, which has been shown to cause respiratory diseases in humans and affect the growth of crops, and for which the Environmental Protection Agency and the California Air Resources Board have set health-protective standards. Ozone is one of the most pervasive pollutants in California, but is not directly emitted. It is formed in the atmosphere from chemical reactions between oxides of nitrogen and hydrocarbons when exposed to sunlight.

Particulate Matter – solid or liquid particles which are small enough to be suspended in the air. Health-based standards have been set by both the Environmental Protection Agency and the California Air Resources Board for particulate matter less than 10 microns in size (PM10 - about 1/7th the thickness of a human hair) which are inhalable into the human lungs; and for particulate matter less than 2.5 microns in size (PM2.5 – one-fourth the size of PM10) which can penetrate deeply into the lungs.

Potential to Emit – the maximum level that a facility or operation can emit based on physical and enforceable limitations. Facilities which can operate around the clock, for example, would have a potential-to-emit based on maximum operation occurring 24 hours a day, 365 days a year.

Precursor Emissions – emissions of pollutants which then react in the atmosphere to form other pollutants for which health-based standards have been established. Key precursors include oxides of nitrogen (forming ozone and particulate matter); volatile organic compounds (forming ozone and particulate matter); and ammonia (forming particulate matter).

Prohibitory Rule – an air pollution control rule which prohibits an activity, operation, or condition in order to prevent or limit pollutant emissions. (This type of rule contrasts with source-specific rules which generally prescribe conditions under which facilities may operate and be granted operating permits.) An example of a prohibitory rule is: "No person shall allow any operation which results in visible emissions exceeding 20% opacity."

Reasonably Available Control Measures (RACM) - the application of methods and techniques to operations and activities, similar to "best available control measures," which achieve a reasonable level of control of a pollutant subject to regulation, taking into account energy, environmental, economic impacts, and other costs, as applicable to the specific activity or operation. In general, RACM are of less stringency than BACM, but for some applications, RACM and BACM may be equivalent.

Sources of Air Pollution – any sources which emit or may emit any air pollutant.

Standard of Performance – a standard for emissions of air pollutants which reflects the degree of emission limitation achievable through the application of the best emission reduction system, accounting for energy, environmental, and cost factors, and which have been adequately demonstrated.

State Implementation Plan (SIP) – documents prepared by states, in cooperation with local air districts, and subject to USEPA approval that identify the actions and programs to be undertaken to control emissions within their boundaries.

Title I – that portion of the Federal Clean Air Act which specifies conditions and requirements for air pollution prevention and control. This is the portion of the FCAA that contains the requirements for New Source Review and need for local permits.

Title V – that portion of the Federal Clean Air Act which specifies the conditions and requirements for federally-required permits which can, under prescribed circumstances, be issued and administered by state or local agencies.

Variance – an authorized allowance for a facility or operation to exceed air pollution control limits, usually for a temporary period of time. Such authorization may be granted by air pollution control agency Hearing Boards, only after making certain findings as specified in state law. An example might be additional time needed by a facility or operation, due to technical issues, to meet limits of a new rule by a specified date.