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Air Quality Planning and Standards

Air Pollution Emissions

The Office of Air Quality Planning and Standards strives to assess the impacts of air pollution emissions and the results of efforts to curb these emissions. The following are some of the topics associated with air pollution emissions:

Air Pollution Models and Estimation Tools

The Clearinghouse for Inventories and Emission Factors (CHIEF) web site includes several tools to help local, state, and federal agencies, environmental consultants, and others who require emission factor information.

The Support Center for Regulatory Air Models (SCRAM) site provides information about mathematical models used to predict the dispersion of air pollution.

The CHIEF Web site makes available other models such as:

  • Water9, which estimates air emissions of individual waste constituents in wastewater collection, storage, treatment, and disposal facilities as well as a database listing many of the organic compounds; and procedures for obtaining reports of constituent fates, including air emissions and treatment effectiveness
  • BEIS, which estimates hourly emissions of biogenic volatile organic compound and soil nitrogen oxide emissions for any county in the contiguous United States
  • ASAP (Area Source Analysis Program)
  • PMCALC, which calculates controlled emissions for filterable PM2.5 and filterable PM10 for point sources

Air Toxics Website (ATW)

Toxic air pollutants are also referred to as air toxics or hazardous air pollutants (HAPs). They are generally defined as those pollutants that are known or suspected to cause serious health problems. "Routine" toxic air pollutants are emitted by a variety of industrial sources and motor vehicles. In addition to routine releases, sudden accidental air releases of toxics potentially threaten many Americans. The Air Toxics Website (ATW) is a central clearinghouse and repository for air toxics information from many different Federal, State, Tribal and Local Agencies performing work in the air toxics arena.

Clearinghouse for Inventories and Emission Factors (CHIEF)

The Clearinghouse for Inventories and Emission Factors (CHIEF Web site) provides access to tools for estimating emissions of air pollutants and preparing air emission inventories. CHIEF serves as EPA's central clearinghouse for the latest information on air emission inventories and emission factors. Emission estimation data bases, newsletters, announcements, and guidance on performing inventories are included in CHIEF.

Compliance and Enforcement

The 1990 Amendments to the Clean Air Act require EPA to develop and enforce rules and regulations for industries and other entities that emit toxic substances into the air. EPA's Compliance and Enforcement program works to satisfy this mandate, with a goal to create a climate for voluntary compliance to succeed. Some of the critical elements of EPA's attempt to create this climate are:

  • Advocate clear enforceable rules
  • Promote coordination and cooperation at all levels of government, regulated industries, and the public
  • Initiate formal enforcement actions at sources posing the most risk of deteriorating the quality of life
  • Promote pollution prevention as a decision of first choice for pollution control and in the design of the regulatory scheme
  • Establish and maintain a highly motivated work force of well trained professionals (Local, State, Federal and Industry)
  • Establish an evaluation system to effectively measure the success of the regulatory scheme and the reduction of risk

Clean Air Technology Center

The Clean Air Technology Center (CATC) serves as a resource on all areas of emerging and existing air pollution prevention and control technologies, and provides public access to data and information on their use, effectiveness and cost. In addition, the CATC will provide technical support, including access to EPA's knowledge base, to government agencies and others, as resources allow, related to the technical and economic feasibility, operation and maintenance of these technologies.

Emission Factors

An emission factor is a representative value that attempts to relate the quantity of a pollutant released into the atmosphere to an activity associated with the release of that pollutant. Such factors may be used in equations to estimate emissions from a process where more specific data is not available. Our Introduction to Emission Factors page contains a more detailed discussion.

The CHIEF web site includes emission factors for both point and area sources, and contains software tools to help people use the factors. The Compilation Of Air Pollutant Emission Factors (AP-42) document series is the principal means by which EPA documents its emission factors. Other tools which use AP-42 factors include the Factor Information Retrieval (FIRE) database, and the Air CHIEF CD-ROM, which includes AP-42 and other estimation tools on one CD-ROM disc.

Emission Inventories

The Clean Air Act Amendments of 1990 recognized that many areas across the United States were in violation of the National Ambient Air Quality Standards (NAAQS). One of the first activities for developing an air quality control strategy for these areas is to prepare an inventory of the emissions of interest.

Ozone, for example, is photochemically produced in the atmosphere when certain "precursor pollutants" (VOC and NOx) are mixed together in the presence of sunlight. To develop an effective ozone control strategy, an air pollution control agency must compile information on the important sources (plants, businesses, etc.) that emit these precursor pollutants. This compilation -- the emission inventory -- identifies the source types present in an area, the amount of each pollutant emitted, the types of processes and control devices employed, and other information.

Emission inventories can serve many purposes. They are used in ambient dispersion modeling and analysis, control strategy development, and in screening sources for compliance investigations. Together with ambient monitoring data, inventory emission estimates have been used as a direct indicator of annual changes in air quality.

OAQPS maintains an inventory called the National EPA Emission Trends (NET) database, composed of ozone period, county-level estimates of point, area, and mobile source emissions. Used with modeling programs, NET data helps EPA to verify the attainment/nonattainment status of areas, analyze regulatory policy, and assess the potential impact of any changes in the NAAQS.

OAQPS also provides various air pollution models and estimation tools which can be used in emission inventory development.

Emissions Measurement Center

The Emissions Measurement Center (EMC) is the EPA's focal point for planning and conducting field test programs to provide quality data in support of regulatory development, producing validated emission test methods, and providing expert technical assistance for EPA, State, and local enforcement officials and industrial representatives involved in emission testing

Emissions Trends Report

National emissions are estimated annually by the EPA based on statistical information about each source category, emission factor, and control efficiency. The estimates are made for over 450 individual source categories that include all major sources of anthropogenic emissions for the years 1900 through 1984. Starting with 1985, the estimates are based on the National EPA Emission Trends (NET) inventory.

The National Air Pollutant Emission Trends report presents the latest estimates of national and regional emissions for criteria air pollutants. Estimates are presented for the years 1900 to 1996, with greater detail in more recent years.

Our Emissions Trends site presents the entire report broken up by chapter in PDF format for downloading and viewing using the Adobe Acrobat viewer.

New Source Review (NSR)

The New Source Review Group manages the development and implementation of requirements under the new source review (NSR) and prevention of significant deterioration (PSD) provisions of the Clean Air Act. These provisions strive to ensure that potential new sources of air pollution (new plants or facilities, or additions to existing ones) take proper steps to minimize pollution levels. The goals of the NSR program are:

  • To ensure that an increase in emissions due to a new source or modification to an existing source does not significantly deteriorate air quality.
  • To ensure that source emissions are consistent with applicable State attainment plans.
  • To ensure that air quality related values are not negatively impacted in areas that have greater pollution problems.
  • To establish control technology requirements that maximize productive capacity while minimizing impacts on air quality.

The NSR website provides material and information pertaining to NSR and PSD issues.


Established by the 1990 amendments to the Clean Air Act, the goal of the Operating Permits Program is to assure that source operators know what air pollution control requirements apply, improve compliance, and resolve applicability questions. The Operating Permits Program Web page provides information about the program and related permit regulations, plus links to the status of state, local, and territorial operating permits programs.

RACT/BACT/LAER Clearinghouse (RBLC)

The RACT (Reasonably Available Control Technology)/BACT (Best Available Control Technology)/LAER (Lowest Achievable Emission Rate) Clearinghouse (RBLC) is designed to provide information about current methods available to industries to try to decrease or minimize pollution. The RBLC was established by OAQPS in 1982 to support the New Source Review program by providing a mechanism for state and local agencies to share their control technology determinations. The RBLC goal is to provide for state and public access to pollution prevention and control technology information and support permitting activities and decision-making by providing timely, current and comprehensive information on alternative technologies.

Support Center For Regulatory Air Models (SCRAM)

The Support Center For Regulatory Air Models (SCRAM) site provides information about mathematical models used to predict the dispersion of air pollution. The site includes computer codes, meteorological input data, documentation and guidance on usage. Its primary purpose is to provide air pollution control agencies with air quality models and related information that support selected requirements of the Clean Air Act.

State Implementation Plans

Section 110 of the Clean Air Act requires each state containing nonattainment areas to develop a written plan for cleaning the air in those areas. This plan, called the State Implementation Plan (SIP), sets forth the state's strategy for getting its air quality within NAAQS standards and keeping it there.

OAQPS' primary role in State Implementation Plans is to:
  • Provide guidance, tools, and assistance to State and local air pollution agencies for developing and implementing the plans
  • Work with the EPA Regional Offices on review and approval of the plans
  • Work with the EPA Regional Offices to ensure that the State/local agencies meet the SIP-related requirements of the Clean Air Act in moving towards attainment of the National Ambient Air Quality Standards.

Emission estimation tools such as AP-42 (Compilation of Air Pollutant Emission Factors) and Regional Oxidant Modeling (ROM) are examples of tools and assistance that OAQPS provides to the State/local agencies for developing their SIPs.



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