The joint associations of ambient air pollutants and weather factors with mortality: Evidence from a national time-stratified case-crossover study in China

Abstract

BackgroundPeople in daily life are usually exposed to multiple environmental factors, but few studies have evaluated the joint health impacts of ambient air pollutants and weather factors. ObjectivesTo investigate the joint associations of short-term exposures to ambient air pollutants and weather factors with mortality and estimate the mortality burden attributable to these multiple environmental exposures in China. MethodsWe collected individual death information from six provinces (Guangdong, Yunnan, Hunan, Zhejiang, Tibet and Jilin) in China during 2013 to 2018, and applied a time-stratified case-crossover study design to estimate the joint associations of air pollutants [PM2.5 (particulate matter with an aerodynamic diameter ≤2.5 μm), O3 (ozone), NO2 (nitrogen dioxide), SO2 (sulfur dioxide), and CO (carbon monoxide)] and weather factors (temperature and relative humidity) with mortality. Air pollutant concentrations on the case day and control days were assessed using a random forest model, and the corresponding temperature and relative humidity data were assessed using a thin plate smoothing model. Excess risks (ER) of exposure to air pollutants and weather factors were estimated using Cox proportional regression models and the attributable fraction (AF) was calculated. ResultsA total of 6,685,146 deaths were enrolled in this study. The overall AF of total mortality attributed to air pollutants (lag03 days) and weather factors (lag021 days) was 16.65 % (95%CI: 16.43 %, 16.87 %), in which the joint AFs attributable to air pollutants and weather factors were 5.31 % (95%CI: 5.08 %, 5.53 %) and 11.34 % (95%CI: 11.12 %, 11.56 %) respectively, and temperature contributed 56 % in the joint effects. Stratified analyses showed greater AFs in females (21.32 %) than in males (14.61 %), and in the elderly (>100 years, 42.34 %) than in young people (21–30 years, 7.67 %). The AFs of mortality from cardiovascular diseases, respiratory diseases, and pneumonia attributed to the joint exposures were 22.72 %, 24.82 % and 33.03 %, respectively. DiscussionThis study provides the joint associations of short-term exposures to both air pollutants and weather factors with mortality risk in China, which has important implications in comprehensively assessing the health impacts of environmental exposures, and taking actions to protect human health.