Independent and combined associations between exposure to ambient air pollutants and mortality: a case-crossover study.

Introduction: Previous studies suggest that short‑term exposure to air pollution is associated with an increased risk of mortality. However, understanding of the combined effects of exposure to various air pollutants on mortality is limited.

Objectives: This study aimed to quantify a short‑term association between exposure to various air pollutants and death risk in the Qingpu District of Shanghai, and to evaluate the modifying effect of ambient temperature on this association.

Patients and methods: We collected daily death records from 2013 to 2019 in the Qingpu District of Shanghai. A time‑stratified case crossover design and conditional logistic regression modeling were employed to estimate death risk associated with exposure to air pollutants. Additionally, we utilized weighted quantile sum regression to identify the predominant air pollutants influencing death risk.

Results: For per 10 μg/m3‑increase in particulate matter less than or equal to 2.5 μm in diameter (PM2.5), 8‑hour moving average concentrations for ozone (O3‑8h), SO2, and NO2 concentrations, the odds ratio (95% CI) of nonaccidental death increased by a maximum of 1.009 (1.002-1.017), 1.017 (1.008-1.027), 1.051 (1.015-1.089), and 1.027 (1.010-1.045), respectively. A majority of air pollutants (excluding CO) were strongly associated with an elevated respiratory death risk, but only O3‑8h and SO2 were positively associated with cardiovascular death at lag‑2 day. There was a significant positive association between the exposure to mixtures of air pollutants and both nonaccidental and respiratory death, with PM2.5 and SO2 identified as major contributors, respectively. Furthermore, the detrimental effects of O3‑8h significantly intensified as temperatures rose.

Conclusions: Environmental exposure to ambient air pollutants was associated with increased death risk, especially at high temperature.