The Effects of Components of Fine Particulate Air Pollution on Mortality in California: Results from CALFINE

Abstract

Objective

Several epidemiologic studies provide evidence of an association between daily mortality and particulate matter < 2.5 μm in diameter (PM _2.5). Little is known, however, about the relative effects of PM _2.5 constituents. We examined associations between 19 PM _2.5 components and daily mortality in six California counties.

Design

We obtained daily data from 2000 to 2003 on mortality and PM _2.5 mass and components, including elemental and organic carbon (EC and OC), nitrates, sulfates, and various metals. We examined associations of PM _2.5 and its constituents with daily counts of several mortality categories: all-cause, cardiovascular, respiratory, and mortality age > 65 years. Poisson regressions incorporating natural splines were used to control for time-varying covariates. Effect estimates were determined for each component in each county and then combined using a random-effects model.

Results

PM _2.5 mass and several constituents were associated with multiple mortality categories, especially cardiovascular deaths. For example, for a 3-day lag, the latter increased by 1.6, 2.1, 1.6, and 1.5% for PM _2.5, EC, OC, and nitrates based on interquartile ranges of 14.6, 0.8, 4.6, and 5.5 μg/m ³, respectively. Stronger associations were observed between mortality and additional pollutants, including sulfates and several metals, during the cool season.

Conclusion

This multicounty analysis adds to the growing body of evidence linking PM _2.5 with mortality and indicates that excess risks may vary among specific PM _2.5 components. Therefore, the use of regression coefficients based on PM _2.5 mass may underestimate associations with some PM _2.5 components. Also, our findings support the hypothesis that combustion-associated pollutants are particularly important in California.