AQ Monitoring Results:
Crockett: Fine Particulate Matter

This page last reviewed September 27, 2010


PM2.5, particles 2.5 microns or smaller, are a subset of PM10 (please refer to the PM10 web page for this monitoring site). They pose an increased health risk because they can deposit deep in the lung and contain substances that are particularly harmful to human health.

Both national and state standards have been established for PM2.5. The standards are levels above which PM2.5 is known to cause adverse health in humans. The current standards are:

Averaging Time California Standards National Standards
24-hour No Separate State Standard 65 ug/m3
Annual Mean 12 ug/m3 15 ug/m3

Currently many Californians are breathing air that violates the federal PM2.5 standards.

Similar to PM10, PM2.5 can be directly emitted or can be formed in the atmosphere when gaseous pollutants such as sulfur dioxide (SO2) and nitrogen dioxide (NO2) undergo chemical reactions in the atmosphere to form secondary PM constituents. On an annual average basis, about half of the PM2.5 is from secondary PM. Major sources of PM2.5 in California include:

  • motor vehicles (i.e. trucks, passenger cars, and off-road equipment); diesel vehicles are a significant source of PM2.5 (including elemental carbon)
  • area wide sources: particles from dust sources tend to fall into the coarse range (PM10) (i.e. windblown dust from open lands; dust from construction, landfills and agriculture); in general, combustion processes form fine particles (PM2.5) (i.e. wood burning stoves and fireplaces; wildfires and brush/waste burning)
  • industrial sources

Ambient Monitoring Results

Ambient levels of PM 2.5 are routinely monitored at approximately 81 sites in the California ambient air quality measurement network. The statewide average concentration of PM 2.5 during 1999-2001 was 16.5 ug/m3 (micrograms per cubic meter). Relative to the statewide average concentration of the daily average 24-hour measurements, the Contra Costa County region was 32% lower for the same time period, averaging 11.2 ug/m3.

The vast majority of PM2.5 BAM data at the John Swett site have been invalidated and so it would not be meaningful to use limited data to summarize the information.