Smog episodes, fine particulate pollution and mortality in China

Starting from early January 2013, northern China was hit by multiple prolonged and severe smog events which were characterized by extremely high-level concentrations of ambient fine particulate matter (PM2.5) with hourly peaks of PM2.5 over 800 µg/m3. However, the consequences of this severe air pollution are largely unknown. This study investigates the acute effect of the smog episodes and PM2.5 on mortality for both urban and rural areas in northern China. We collected PM2.5, mortality, and meteorological data for 5 urban city districts and 2 rural counties in Beijing, Tianjin and Hebei Province of China from January 1, 2013 through December 31, 2013. We employed the generalized additive models to estimate the associations between smog episodes or PM2.5 and daily mortality for each district/county. Without any meteorological control, the smog episodes are positively and statistically significantly associated with mortality in 5 out of 7 districts/counties. However, the findings are sensitive to the meteorological factors. After controlling for temperature, humidity, dew point and wind, the statistical significance disappears in all urban districts. In contrast, the smog episodes are consistently and statistically significantly associated with higher total mortality and mortality from cardiovascular/respiratory diseases in the two rural counties. In Ji County, a smog episode is associated with 6.94% (95% Confidence Interval, −0.20 to 14.58) increase in overall mortality, and in Ci County it is associated with a 19.26% (95% CI, 6.66–33.34) increase in overall mortality. The smog episodes kill people primarily through its impact on cardiovascular and respiratory diseases. On average, a smog episode is associated with 11.66% (95% CI, 3.12–20.90) increase in cardiovascular and respiratory mortality in Ji County, and it is associated with a 22.23% (95% CI, 8.11–38.20) increase in cardiovascular and respiratory mortality in Ci County. A 10 μg/m3 increase in PM2.5 concentration is associated with 0.88% (95% CI, 0.3–1.46) increase in overall mortality and 1.2% (95% CI, 0.55–1.85) in Ji County. A 10 μg/m3 increase in PM2.5 concentration is associated with 0.55% (95% CI, −0.02 to 1.13) increase in overall mortality in Ci County. The findings suggest that the smog episodes and fine particulate have bigger and more detrimental impacts on rural residents, especially for those living close to big and polluted cities. The smog episodes and PM2.5 are statistically associated with mortality in rural areas of China. The associations for urban areas are not statistically significant.