The Ambient Air Monitoring Program

Between the years 1900 and 1970, the emission of six principal pollutants increased significantly. These six pollutants, also called criteria pollutants, are: particulate matter, sulfur dioxide, carbon monoxide, nitrogen dioxide, ozone, and lead. In 1970, the Clean Air Act (CAA) was signed into law. The CAA and its amendments provides the framework for all pertinent organizations to protect air quality. EPA's principal responsibilities under the CAA, as amended in 1990 include:

• setting National Air Quality Standards (NAAQS) for pollutants considered harmful to the public health and environment
• ensuring the air quality standards are met or attained (in cooperation with the States) through national standards and strategies to control air emission standards from sources
• ensuring the sources of toxic air pollutants are well controlled
• monitoring the effectiveness of the program.

• To judge compliance with and/or progress made towards meeting ambient air quality standards.
• To activate emergency control procedures that prevent or alleviate air pollution episodes.
• To observe pollution trends throughout the region, including non-urban areas.
• To provide a data base for research evaluation of effects: urban, land-use, and transportation planning; development and evaluation of abatement strategies; and development and validation of diffusion models.

1. To determine highest concentrations expected to occur in the area covered by the network;
2. to determine representative concentrations in areas of high population density;
3. to determine the impact on ambient pollution levels of significant sources or source categories; and
4. to determine general background concentration levels.

The EPA's ambient air quality monitoring program is carried out by State and local agencies and consists of three major categories of monitoring stations, State and Local Air Monitoring Stations (SLAMS), National Air Monitoring Stations (NAMS), and Special Purpose Monitoring Stations (SPMS), that measure the criteria pollutants. Additionally, a fourth category of a monitoring station, the Photochemical Assessment Monitoring Stations (PAMS), which measures ozone precursors (approximately 60 volatile hydrocarbons and carbonyl) has been required by the 1990 Amendments to the Clean Air Act.

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The SLAMS consist of a network of ~ 4,000 monitoring stations whose size and distribution is largely determined by the needs of State and local air pollution control agencies to meet their respective State implementation plan (SIP) requirements.

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The NAMS (1,080 stations) are a subset of the SLAMS network with emphasis being given to urban and multi-source areas. In effect, they are key sites under SLAMS, with emphasis on areas of maximum concentrations and high population density.

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Special Purpose Monitoring Stations provide for special studies needed by the State and local agencies to support State implementation plans and other air program activities. The SPMS are not permanently established and, can be adjusted easily to accommodate changing needs and priorities. The SPMS are used to supplement the fixed monitoring network as circumstances require and resources permit. If the data from SPMS are used for SIP purposes, they must meet all QA and methodology requirements for SLAMS monitoring.

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A PAMS network is required in each ozone nonattainment area that is designated serious, severe, or extreme. The required networks will have from two to five sites, depending on the population of the area. There will be a phase-in period of one site per year starting in 1994. The ultimate PAMS network could exceed 90 sites at the end of the 5-year phase-in period.

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