PM2.5 Monitoring Network Design for California

This page last reviewed January 15, 2009

The California Air Resources Board (ARB), in partnership with California's air quality management districts, has developed a PM2.5 monitoring network to implement the PM2.5 California and National Ambient Air Quality Standards (CAAQS and NAAQS). The term PM2.5 applies to airborne particles with aerodynamic diameters less than 2.5 microns.

Particulate Matter Monitoring Network Descriptions

The ARB submitted the 2002 California PM2.5 Monitoring Network Description to the U.S. EPA Region IX for approval. This report provides an overview of the network and outlines plans for expanding and improving the PM2.5 monitoring network in California through June 2004.

The 2002 Network Description is the fifth PM2.5 network description in California. The four previously submitted network descriptions are for  199819992000 and  2001.

Program Goal and Objectives:

The goal of the PM2.5 monitoring program is to provide ambient data that support the State and national air quality programs. These data include mass measurements and chemically resolved, or speciated data. Mass measurements are used principally for comparison to the PM2.5 CAAQS and NAAQS. These comparisons identify areas that do or do not meet the PM2.5 standards, thereby allowing areas to be designated as attainment or nonattainment. Speciated data support the development of emission mitigation strategies intended to reduce ambient PM2.5 levels. The data are used to evaluate emissions inventory and air quality models, analyze source attribution, and track the success of emission control programs.

The PM2.5 network is designed to enable the air quality management community in California to collect ambient PM2.5 data as required by Title 40 of the Code of Federal Regulations (40 CFR), Parts 50, 53, and 58 published in the Federal Register on July 18, 1997. (Refer to the U.S. EPA for the specific rules.)

PM2.5 Monitoring Network in California

During 1998, the first year of the PM2.5 monitoring program, the ARB and the air districts proposed establishing 78 Federal Reference Method (FRM) monitoring sites around the state. Since then, the PM2.5 monitoring network has been expanded to include three additional sites with FRM samplers and a limited number of continuous samplers and speciation samplers. By the end of 2002, continuous PM2.5 mass monitors were deployed to 33 sites, and filter-based speciation samplers were deployed to 17 sites. By June of 2004, we plan to add continuous PM2.5 mass monitors to 11 sites.

Monitoring Planning Areas and Monitoring Sites

The ARB and the air districts established 18 Monitoring Planning Areas in the state. These MPAs have been used for locating the PM2.5 monitoring sites throughout California.


Please send questions or comments to ARB's Air Quality Data Program.


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