Seasonal variation in the acute effect of particulate air pollution on mortality in the China Air Pollution and Health Effects Study (CAPES)

Epidemiological findings concerning the seasonal variation in the acute effect of particulate matter (PM) are inconsistent. We investigated the seasonality in the association between PM with an aerodynamic diameter of less than 10μm (PM₁₀) and daily mortality in 17 Chinese cities. We fitted the "main" time-series model after adjustment for time-varying confounders using smooth functions with natural splines. We established a "seasonal" model to obtain the season-specific effect estimates of PM₁₀, and a "harmonic" model to show the seasonal pattern that allows PM₁₀ effects to vary smoothly with the day in a year. At the national level, a 10μg/m³ increase in the two-day moving average concentrations (lag 01) of PM₁₀ was associated with 0.45% [95% posterior interval (PI), 0.15% to 0.76%], 0.17% (95% PI, -0.09% to 0.43%), 0.55% (95% PI, 0.15% to 0.96%) and 0.25% (95%PI, -0.05% to 0.56%) increases in total mortality for winter, spring, summer and fall, respectively. For the smoothly-varying plots of seasonality, we identified a two-peak pattern in winter and summer. The observed seasonal pattern was generally insensitive to model specifications. Our analyses suggest that the acute effect of particulate air pollution could vary by seasons with the largest effect in winter and summer in China. To our knowledge, this is the first multicity study in developing countries to analyze the seasonal variations of PM-related health effects.