Short-term exposure to fine particulate matter constituents and mortality: case-crossover evidence from 32 counties in China.

A growing number of studies associated increased mortality with exposures to specific fine particulate (PM _2.5 ) constituents, while great heterogeneity exists between locations. In China, evidence linking PM _2.5 constituents and mortality was extensively sparse. This study primarily aimed to quantify short-term associations between PM _2.5 constituents and non-accidental mortality among the Chinese population. We collected daily mortality records from 32 counties in China between January 1, 2011, and December 31, 2013. Daily concentrations of main PM _2.5 constituents (organic carbon (OC), elemental carbon (EC), nitrate (NO ₃ ^- ), sulfate (SO ₄ ^2- ), and ammonium (NH ₄ ⁺ )) were estimated using the modified Community Multiscale Air Quality model. Time-stratified case-crossover design with conditional logistic regression models was adopted to estimate mortality risks associated with short-term exposures to PM _2.5 mass and its constituents. Stratification analyses were done by sex, age, and season. A total of 116,959 non-accidental deaths were investigated. PM _2.5 concentrations on the day of death were averaged at 75.7 µg m ^-3 (control day: 75.6 µg m ^-3 ), with an interquartile range (IQR) of 65.2 µg m ^-3 . Per IQR rise in PM _2.5 , EC, OC, NO ₃ ^- , SO ₄ ^2- , and NH ₄ ⁺ at lag-04 day was associated with an increase in non-accidental mortality of 2.4% (95% confidence interval, (1.0-3.7), 1.7% (0.8-2.7), 2.9% (1.6-4.3), 2.1% (0.4-3.9), 1.0% (0.2-1.9), and 1.6% (0.3-2.9), respectively. Both PM _2.5 mass and its constituents were strongly associated with elevated cardiovascular mortality risks, but only PM _2.5 , EC, and OC were positively associated with respiratory mortality at lag-3 day. PM _2.5 mass and its constituents associated effects on mortality varied among sex- and age-specific subpopulations. Differences in the seasonal pattern of associations exist among PM _2.5 constituents, with stronger effects related to EC and NO ₃ ^- in warm months but SO ₄ ^2- and NH ₄ ⁺ in cold months. Short-term exposures to PM _2.5 compositions were positively associated with increased risks of mortality, particularly those constituents from combustion-related sources.
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