PM2.5
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There are two federal primary standards for PM2.5 (fine particulate matter) - an annual average standard of 9.0 ug/m3 and a 24-hour average standard of 35 ug/m3. There are two federal secondary standards - an annual standard of 15 ug/m3 and a 24-hour standard of 35 ug/m3 (the same as the primary). Detailed information regarding the federal particulate matter (PM) standards can be found on the U.S. EPA website.
In February 2024, U.S. EPA lowered the federal primary PM2.5 annual standard to 9.0 ug/m3 from the 12.0 ug/m3 standard set in 2012. The secondary annual standard remains at 15.0 ug/m3. States and Tribal Authorities will submit initial recommendations of areas that do not attain this standard (i.e., nonattainment areas) to U.S. EPA by February 2025, and U.S. EPA will finalize area designations by February 2026. The steps in this process can be found in the 2024 9.0 ug/m3 Annual PM2.5 Standard section below.
Annual Standard. In February 2024, U.S. EPA lowered the federal primary PM2.5 annual standard from 12.0 ug/m3 to 9.0 ug/m3; the secondary annual standard remained at 15 ug/m3. Current area designation information can be found on U.S. EPA's website.
24-Hour Standard. In December 2006, U.S. EPA lowered the federal 24-hour PM2.5 standard from 65 ug/m3 to 35 ug/m3; the secondary 24-hour standard is the same as the primary. Current area designation information can be found on U.S. EPA's website.
Maps of current area designations for the 2012 annual and 2006 24-hour standards can be found through the Resources tab on the left. These maps will be updated to include the 2024 9.0 ug/m3 annual PM2.5 standard when these designations have been finalized in early 2026. Information about specific PM2.5 nonattainment areas and the efforts to bring them into attainment of the federal PM2.5 standards can be found on the California State Implementation Plan (SIP) webpage.
2024 9.0 ug/m3 Annual PM2.5 Standard
- November 2027 - Moderate Area State Implementation Plans (SIPs) due for areas designated as nonattainment
- CARB supporting website: SIPs for the 9 ug/m3 PM2.5 Standard
- February 2026 - U.S. EPA will issue final area designations
- February 2025 - CARB will submit initial recommendations for area designations
- December 2024/January 2025 - CARB will hold a public hearing to consider initial area designation recommendations
- Fall 2024 - CARB will hold public workshops on the area designation process and the initial area designation recommendations
- February 2024 - U.S. EPA issued final revised PM2.5 NAAQS (effective May 6, 2024)
- Federal Register Notice (89 FR 16202)
2012 12.0 ug/m3 Annual PM2.5 Standard
- January 2015 - U.S. EPA issued final area designations (effective April 15, 2015)
- August 2014 - U.S. EPA responded to CARB area designations recommendations
- Letter and Response (issued August 19, 2014)
- November 2013 - CARB submitted initial recommendations for area designations
- Letter to U.S. EPA (November 25, 2013)
- Enclosure - Staff Report: PM2.5 Area Recommendations for the Revised Federal PM2.5 Annual Standard
- November 2013 - CARB held a public hearing (November 21, 2013) to consider the proposed recommendations
2006 35 ug/m3 24-Hour PM2.5 Standard
- July 2018 - U.S. EPA redesignated the Chico Planning Area to attainment (for further information, see the Butte County Air Quality Management Plans page on CARB's website)
- December 2014 - U.S. EPA redesignated the Yuba City-Marysville Planning Area to attainment (for further information, see the Feather River Air Quality Management Plans page on CARB's website)
- February 2011 - U.S. EPA issued revised area designations
- November 2009 - U.S. EPA issued final area designations (effective December 14, 2009)
- Federal Register Notice
- Map showing 24-hour PM2.5 Nonattainment Areas (located on U.S. EPA website)
- October 2008 - CARB submitted additional analysis for area designation recommendations
- Letter (signed October 15, 2008)
- Enclosure 1 - Technical Support - PM2.5 Designations Recommendations
- Letter (signed October 15, 2008)
- August 2008 - U.S. EPA responded to CARB area designation recommendations
- Letter and Response (issued August 18, 2008)
- December 2007 - CARB submitted initial recommendations for area designations
- Letter (issued December 17, 2007)
- Enclosure 1 - Initial Recommendations for Area Designations Under the Revised Federal PM2.5 Standard
- Enclosure 2 - Staff Report: Nonattainment Area Designation for the Revised Federal PM2.5 Standard
- Enclosure 3 - Information to Support Recommendations for Federal PM2.5 Nonattainment Area Boundaries
- Enclosure 4 - Boundary Descriptions for Recommended Nonattainment Areas under the Federal PM2.5 Standard
- Enclosure 5 - PM2.5 Monitoring Data Summary, 2004-2006
- December 2007 - CARB held a public hearing (December 6-7, 2007)
- Hearing Notice
- Staff Report
- Potential Exceptional Events: U.S. EPA guidance allows for the exclusion from regulatory determinations of air quality data affected by exceptional events. Since U.S. EPA based their final nonattainment area designations on 2005-2007 PM2.5 air quality monitoring data, CARB submitted 2007 calendar year exceptional events documentation. This document addresses monitoring days which may have been impacted by wildfires late in 2007 for areas in which the data may affect their designation status.
1997 65 ug/m3 24-Hour PM2.5 Standard and 15 ug/m3 Annual PM2.5 Standard
- April 2005 - U.S. EPA finalized PM2.5 area designations
- Based on 2002-2004 PM2.5 air quality monitoring data, the South Coast Air Basin and the San Joaquin Valley Air Basin were designated nonattainment for both the 24-hour and annual PM2.5 standards.
- February 2004 - CARB submitted recommendations for PM2.5 area designations
- Letter (issued February 11, 2004)
- Enclosure 1 - Initial Recommendations for Area Designations under the Federal PM2.5 Standard
- Enclosure 2 - Information to Support Recommendations for Federal PM2.5 Nonattainment Area Boundaries
- Enclosure 3 - Boundary Descriptions for Recommended Nonattainment Areas under the Federal PM2.5 Standard
- Enclosure 4 - PM2.5 Monitoring Data Summary (2000-2002)