California Report Bumps Up Estimates of Premature Deaths from Particle Pollution
A draft report from the California Air Resources Board (CARB) has estimated that 14,000 to 24,000 premature deaths each year are attributable to fine particle air pollution (PM2.5). The report reevaluated all the relevant scientific literature to develop an updated relative risk factor for PM2.5 exposures. Earlier CARB and U.S. EPA estimates had relied on the results from the American Cancer Society cohort study (Pope et al. 1995, 2002)) to estimate premature deaths. New epidemiological studies have reported a stronger relationship between PM2.5 and premature death. These include the analysis by Jerrett et al. (2005) of the Los Angeles region, and the extended follow up of the Harvard Six Cities study by Laden et al. (2006). In addition, the report considered an expert elicitation conducted by EPA to characterize the range of the concentration-response function and uncertainty around that range. The concentration-response function relates changes in exposure to ambient concentrations of PM to changes in an adverse effect, in this case, mortality. Based on this review, the report recommends a new relative risk factor of a 10 percent increase in premature death per 10 microgram per cubic meter increase in PM2.5 exposures, with an uncertainty interval of 3 percent to 20 percent.
Next, the report used a systematic approach for deriving a cutpoint, that is, the lowest level of PM2.5 that can be assumed to be associated with premature death in risk or benefits analyses. There is no evidence for a threshold (the level below which no increased risk occurs) in the current scientific studies, so various assumptions are often made about cutpoints. This report examines several possible cutpoint levels. 2.5 micrograms per cubic meter is the natural background level of fine particles in California. 7 micrograms per cubic meter is the lowest concentration observed in the American Cancer Society cohort study. So the report recommends that estimates be based on a range of cutpoints from 2.5 to 7 micrograms per cubic meter.
Using this approach PM2.5 air pollution is associated with about 14,000 to 24,000 premature deaths annually in California. Taking into account the uncertainty interval, estimates could range from 4,300 to 41,000 deaths.
The draft report is available online. It will be subject to public comment and review. For more information, click here:
California Environmental Protection Agency, Air Resources Board. Methodology for Estimating Premature Deaths Associated with Long-term Exposures to Fine Airborne Particulate Matter in California. Draft Staff Report May 22, 2008.
