2008 Northern California Wildfires

This page last reviewed January 27, 2014

satellite view of California Wildfire 2008

Event Description

During the summer of 2008, extreme fuel conditions in Northern and Central California and an unusually intensive outbreak of lightning strikes from a series of dry thunderstorms combined for an unprecedented summer fire season. All of Northern California, and much of Central California, was affected, with smoke and haze lingering over the region for much of the summer.

Numerous monitoring sites, comprising both Federal Reference Method (FRM) and Federal Equivalent Method (FEM) monitors, recorded almost daily elevated particulate matter (PM) concentration levels, with many days above the National Ambient Air Quality Standards (NAAQS) for both PM2.5 and PM10, an unusual occurrence in the summer. In addition, although summer is a traditionally high ozone season, ozone monitors throughout the region showed the additional impact of the wildfires, with many monitors exceeding the NAAQS.

ARB requested exclusion of PM data from over 30 monitoring sites in 15 Air Districts where smoke caused levels to exceed those historically seen during the summer low particulate season. Exclusion of ozone data was also requested for sites in the Sacramento Metropolitan region.

Regulatory Background

The Code of Federal Regulations (CFR) provides the definition and criteria for determining whether air quality data is impacted by an exceptional event. The 40 CFR 50.1 (j)1 definition states that “exceptional event means an event that affects air quality, is not reasonably controllable or preventable, is an event caused by human activity that is unlikely to recur at a particular location or a natural event, and is determined by the Administrator in accordance with 40 CFR 50.14 to be an exceptional event.” The demonstration to justify data exclusion as outlined in 40 CFR 50.14 specifies that evidence must be provided to show that:

  1. The event meets the definition of an exceptional event;
  2. There is a clear causal relationship between the measurement under consideration and the event that is claimed to have affected air quality in the area;
  3. The event is associated with a measured concentration in excess of normal historical fluctuations, including background; and,
  4. There would have been no exceedance or violation but for the event.

Official PM2.5 and PM10 Exceptional Events Documentation Submitted to U.S. EPA 

Official Ozone Exceptional Events Documentation Submitted to U.S. EPA March 30, 2011


Additional Web-based Information regarding the 2008 Northern California Wildfires (not part of official documentation)