Airborne Fine Particulate Matter and Short-Term Mortality: Exploring the California Experience,2007-2010.
The U.S. Environmental Protection Agency regulates ambient airborne fine particulate matter (PM2.5) on the basis that it is causally associated with short-term mortality — i.e., daily increases in PM2.5 cause increases in daily deaths. This is the first epidemiologic study to test that hypothesis on a systematic basis, i.e., using all the relevant and available data from a large contiguous geographic area. Based on a comparison of air quality data from the California Air Resources Board and death certificate data for 854,109 deaths from the California Department of Public Health for the years 2007-2010, no correlation was identified between changes in ambient PM2.5 and daily deaths, including when the analysis was limited to the deaths among the elderly, heart and/or lung deaths only, and heart and/or lung deaths among the elderly. Although this is only an epidemiologic or statistical study that cannot absolutely exclude the possibility that PM2.5 actually affects mortality in some small and as yet unknown way, these results also illustrate that it would be virtually impossible to demonstrate through epidemiologic study that such an effect actually exists. Notwithstanding the limits of the epidemiologic method, if a significant causal relationship between PM2.5 and mortality existed, that relationship should have been visible in this study. But it was not.