AQ Monitoring Results:
Fresno: Fine Particulate Matter
This page last reviewed October 13, 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 PM2.5 are routinely monitored at approximately 81 sites in the California ambient air quality measurement network. The statewide average concentration of PM2.5 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 Fresno
County region was 31% higher for the same time period, averaging 21.7 ug/m3. Note that the data for the routine PM2.5 sites are based on a 24-hour filter monitoring method, while the data for Fremont School are based on an hourly method known as BAM2.5. A daily average was computed for BAM2.5 data to compare with the filter data.
The ambient monitoring results at Fremont School are provided here:
- A graph comparing the monthly summaries of PM2.5 at the community with historical statewide and regional levels.
- A table of summary statistics
- Raw data in Excel format