What is particulate matter?

Particulate matter (PM) is a mixture of solid particles and liquid droplets in the air. The size of PM is directly linked to potential health problems. EPA has set federal standards for PM10 (PM that is 10 microns or less in diameter) and PM2.5 (PM that 2.5 microns or less in diameter. Health research has also documented health effects of ultrafine particles, or particles that are 0.1 microns or smaller.

The chemical composition of PM is also a factor in the type and severity of health impacts. PM can be emitted directly into the atmosphere, or it can form in the atmosphere through the photochemical reactions of precursors. There are several PM species, or chemical compounds, including organic carbon, elemental carbon, geologic material, trace metals, secondary organic aerosols, ammonium nitrate, and ammonium sulfate. More information is available on EPA’s website.

Adopted PM Plans

• 2012 PM2.5 Plan
  The District adopted the 2012 PM2.5 Plan in December 2012. This plan addresses EPA’s 24-hour PM2.5 standard of 35 µg/m^³, which was established by EPA in 2006.
  
  
• 2008 PM2.5 Plan
  The District adopted the 2008 PM2.5 Plan in April 2008. This plan addresses EPA’s annual PM2.5 standard of 15 µg/m^³, which was established by EPA in 1997.
  
  
• 2007 PM10 Maintenance Plan
  The District adopted the 2007 PM10 Maintenance Plan in September 2007 to assure the San Joaquin Valley’s continued attainment of EPA’s PM10 standard. EPA designated the Valley as an attainment/maintenance area for PM10.