Air pollution and daily mortality in the Multi-country Multi-city study: single and joint effect with heat

Abstract

Background and Aim: The relationship between air pollution and daily mortality remains to be determined at a global scale. Moreover, few studies reported the interaction between air pollution and heat on mortality. Methods: We collected daily air pollution, temperature, and mortality data from the Multi-country Multi-city (MCC) network. The air pollutants included particulate matter (PM) with aerodynamic diameter <= 10 μm (PM10) and <= 2.5 μm (PM2.5), ozone (O3), carbon monoxide (CO), nitrogen dioxide (NO2), and sulfur dioxide (SO2). We applied a two-stage time-series analysis, with over-dispersed generalized linear models and multilevel meta-analysis. The joint effect between air temperature and pollutants was analyzed in the warm season, with product terms between non-linear air temperature and linear air pollutants. Results: We observed significant associations of air pollution with daily mortality. For instance, 10 μg/m3 increase in the 2-day moving average of PM2.5 and O3 concentrations were associated with increases of 0.44% (95% confidence interval [CI], 0.39 to 0.50) and 0.18% (95%CI, 0.12 to 0.24) in daily all-cause mortality, respectively. We also found evidence of interaction between heat and air pollution. For example, an increase in mean temperature from 75th to 99th percentile was associated with 9.0% (95%CI: 7.1%, 11.0%), 10.4% (95%CI: 8.4%, 12.4%), and 13.6% (95%CI: 10.6%, 16.6%) increases in mortality when PM10 was equal to 5th, 50th and 95th percentiles. Similarly, 10 μg/m3 increment in PM10 was associated with a 0.24% (95%CI: 0.02%, 0.46%), 0.46% (95%CI: 0.34%, 0.59%), and 0.76% (95%CI: 0.42%, 1.11%) increases in mortality when air temperature was at 5th, 50th and 95th percentiles, respectively. Conclusions: We found robust evidence on the short-term effects of air pollution on daily mortality. We also found evidence of effect modification between air temperature and air pollutants on mortality during the warm period. Keywords: Mortality, Short-term Exposure, Temperature, Air pollution, Effect modification