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

TLDR

Epidemiologic studies link daily mortality to PM2.5, yet the relative effects of its constituents are poorly understood, with stronger associations observed for sulfates and metals during cool seasons. The study aimed to evaluate how 19 PM2.5 components influence daily all‑cause, cardiovascular, respiratory, and older‑age mortality in six California counties. Daily mortality and PM2.5 component data from 2000‑2003 were analyzed with Poisson regression incorporating natural splines to adjust for time‑varying covariates. Random‑effects analysis revealed that PM2.5 mass and several constituents, especially cardiovascular deaths, were associated with mortality; for a 3‑day lag, PM2.5, EC, OC, and nitrates increased deaths by 1.6–2.1%, and combustion‑associated pollutants like sulfates and metals had stronger effects in cool seasons, suggesting mass‑based coefficients may underestimate component risks.

Abstract

Several epidemiologic studies provide evidence of an association between daily mortality and particulate matter < 2.5 pm in diameter (PM2.5). Little is known, however, about the relative effects of PM2.5 constituents. We examined associations between 19 PM2.5 components and daily mortality in six California counties.We obtained daily data from 2000 to 2003 on mortality and PM2.5 mass and components, including elemental and organic carbon (EC and OC), nitrates, sulfates, and various metals. We examined associations of PM2.5 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.PM2.5 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 PM2.5, EC, OC, and nitrates based on interquartile ranges of 14.6, 0.8, 4.6, and 5.5 pg/m(3), respectively. Stronger associations were observed between mortality and additional pollutants, including sulfates and several metals, during the cool season.This multicounty analysis adds to the growing body of evidence linking PM2.5 with mortality and indicates that excess risks may vary among specific PM2.5 components. Therefore, the use of regression coefficients based on PM2.5 mass may underestimate associations with some PM2.5 components. Also, our findings support the hypothesis that combustion-associated pollutants are particularly important in California.