Monitoring Pollutant Concentration in the Ambient Air

FigureThe 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.

One way to protect and assess air quality is through the development of an Ambient Air Monitoring Program. Currently the air quality monitoring networks in the United States focus on the criteria pollutants, as well as the relevant ambient air pollution information for visibility impairment and acid rain. Although there is currently no national air toxic monitoring network, there are approximately 300 monitoring sites currently producing ambient data on some of the 188 hazardous air pollutants (HAPs). EPA is working together with state, tribal, and local monitoring agencies to build upon the existing monitoring sites to develop a national air toxic monitoring network.

The EPA's ambient air quality monitoring program is carried out by state, tribal, 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). An additional fourth category of monitoring stations, Photochemical Assessment Monitoring Station (PAMS), was added by requirement of the CAA 1990 Amendments.

The SLAMS were established to allow state or local governments to develop monitoring networks tailored more to their immediate ambient air monitoring needs related with the State implementation plans (SIPs).

Figure: The NAMS network consists of 1,080 stations with emphasis being given to urban and multi-source areas.

The SLAMS consist of a network of approximately 4,000 monitoring stations. The NAMS are a subset of the SLAMS network with emphasis being given to urban and multi-source areas. There are nearly 1,080 NAMS stations across the nation. SPMS are stations used by state and local agencies to fulfill specific short-term monitoring goals. The SPMS are not permanently established and can be adjusted easily to accommodate changing needs and priorities. A PAMS network is required for more extensive monitoring of ozone and its precursors in areas with high ozone levels. As of 2002, there were 22 PAMS operating networks sites.

Air monitoring sites can sample the air continuously, daily, or periodically to assess both peak concentrations and overall trends, and are reported in the Air Quality Subsystem (AQS) database.

Figure: Interagency Monitoring of Protected Visual Environments (IMPROVE) network collects data to characterize visibility at national parks and protected areas.

Figure: A PAMS network is required in each ozone nonattainment area that is designated serious, severe, or extreme.

More information on air pollution monitoring can be found at http://www.epa.gov/oar/oaqps/montring.html

A Continuous Emissions Monitoring System (CEMS)
is the total equipment necessary for the determination of a gas or particulate matter concentration or emission rate using pollutant analyzer measurements and a conversion equation, graph, or computer program to produce results in units of the applicable emission limitation or standard. CEMS are required under some of the EPA regulations for either continual compliance determinations or determination of exceedances of the standards. The individual subparts of the EPA rules specify the reference methods that are used to substantiate the accuracy and precision of the CEMS.