Associations between mortality and prolonged exposure to elevated particulate matter concentrations in East Asia

Previous epidemiological studies regarding mortality and particulate matter with an aerodynamic diameter of < 10 μm (PM10) have considered only absolute concentrations of PM10 as a risk factor. However, none have evaluated the durational effect of multi-day periods with high PM10 concentrations. To evaluate the durational effect (i.e., number of days) of high PM10 concentrations on mortality, we collected data regarding 3,662,749 deaths from 28 cities in Japan, South Korea, and China (1993-2009). Exposure was defined as consecutive days with daily PM10 concentrations ≥ 75 μg/m3. A Poisson model was used with duration as the variable of interest, while controlling for daily PM10 concentrations, meteorological variables, seasonal trends, and day of the week. The increase in mortality risk for each additional consecutive day with PM10 concentrations ≥ 75 μg/m3 was 0.68% in Japan (95% confidence interval [CI]: 0.35-1.01%), 0.48% in South Korea (95% CI: 0.30-0.66%), and 0.24% in China (95% CI: 0.14-0.33%). The annual average maximum number of consecutive days with high PM10 in Japan (2.40 days), South Korea (6.96 days), and China (42.26 days) was associated with non-accidental death increases of 1.64% (95% CI: 1.31-1.98%), 3.37% (95% CI: 3.19-3.56%), and 10.43% (95% CI: 10.33-10.54%), respectively. These findings may facilitate the planning of public health interventions to minimize the health burden of air pollution.