PM2.5 Monitoring Sites in California

This page last reviewed August 26, 2003

The PM2.5 monitoring network includes multiple elements with different, yet overlapping objectives. The two main elements of the network are the mass and chemical speciation networks.

The type of monitor used to measure PM2.5 mass concentrations depends on the monitoring objective. Federal Reference Method (FRM) gravimetric filter-based samplers are the only samplers currently approved to provide data for determining the attainment status for an area. Continuous mass monitors are used to collect data for understanding diurnal and episodic behavior of fine particles, transport assessment, and for use by health scientists investigating exposure patterns.

The major objectives for the chemical speciation program are to develop emission control strategies, track trends of selected PM2.5 constituents over time, and assist in health studies and other ambient aerosol research. The chemical speciation network uses multiple instruments, from traditional filter-based to chemical-specific continuous instruments, to measure concentrations of significant PM2.5 constituents, including trace elements, sulfate, nitrate, sodium, potassium, ammonium, and carbon.

The table below outlines the major network elements.

PM2.5 Network Elements

Network Element Target Species Sampling Frequency Site Deployment Status
Mass Concentration
FRM Mass Mass Everyday,
one-in-3 day,
or one-in-6 day
81 deployed
Continuous Mass Mass Continuous 33 deployed,
11 planned
Filter Based Speciation
NAMS Elements, Ions, Carbonaceous Aerosols One-in-3 day 7 deployed
SLAMS Elements, Ions, Carbonaceous Aerosols One-in-3 day
or one-in-6 day
10 deployed
IMPROVE Elements, Ions, Carbonaceous Aerosols One-in-6 day 17 deployed,
1 planned

Detailed listings of the PM2.5 monitoring sites, types of monitors deployed at each site, and a summary of PM2.5 mass data collected at each FRM site are available to download in the following three documents:

  • Appendix A (30K PDF), which provides a table of FRM sites in California along with the operating agency, type of monitor, date of first valid sample, sampling schedule, and supporting lab.
  • Appendix B (36K PDF), which includes a table of existing and planned PM2.5 monitoring sites in California along with types of PM2.5 mass and speciation samplers operating at each site.
  • Appendix C (88K PDF), which includes a summary of PM2.5 FRM mass data at each monitoring site.

The 2002 California PM2.5 Monitoring Network Description also includes a map showing the locations of the 81 FRM sites and a map showing the locations of the continuous mass monitoring sites.


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


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