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 <10μm (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 ≥75μg/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 ≥75μg/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 (2.40days), South Korea (6.96days), and China (42.26days) 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.