Temperature modifies the acute effect of particulate air pollution on mortality in eight Chinese cities Original Research Article

Background Both temperature and particulate air pollution are associated with increased death risk. However, whether the effect of particulate air pollution on mortality is modified by temperature remains unsettled. Methods A stratified time-series analysis was conducted to examine whether the effects of particulate matter less than 10 μm in aerodynamic diameter (PM10) on mortality was modified by temperature in eight Chinese cities. Poisson regression models incorporating natural spline smoothing functions were used to adjust for long-term and seasonal trends of mortality, as well as other time-varying covariates. The bivariate response surface model was applied to visually examine the potential interacting effect. The associations between PM10 and mortality were stratified by temperature to examine effect modification. Results The averaged daily concentrations of PM10 in the eight Chinese cities ranged from 65 μg/m3 to 124 μg/m3, which were much higher than in Western countries. We found evidence that the effects of PM10 on mortality may depend on temperature. The eight-city combined analysis showed that on “normal” (5th–95th percentile) temperature days, a 10-μg/m3 increment in PM10 corresponded to a 0.54% (95% CI, 0.39 to 0.69) increase of total mortality, 0.56% (95% CI, 0.36 to 0.76) increase of cardiovascular mortality, and 0.80% (95% CI, 0.64 to 0.96) increase of respiratory mortality. On high temperature (> 95th percentile) days, the estimates increased to 1.35% (95% CI, 0.80 to 1.91) for total mortality, 1.57% (95% CI, 0.69 to 2.46) for cardiovascular mortality, and 1.79% (95% CI, 0.75 to 2.83) for respiratory mortality. We did not observe significant effect modification by extreme low temperature. Conclusions Extreme high temperature increased the associations of PM10 with daily mortality. These findings may have implication for the health impact associated with both air pollution and global climate change.