High temperatures enhanced acute mortality effects of ambient particle pollution in the "oven" city of Wuhan, China

BACKGROUND: We investigated whether the effect of air pollution on daily mortality is enhanced by high temperatures in Wuhan, China, using data from 2001 to 2004. Wuhan has been called an "oven" city because of its hot summers. Approximately 4.5 million permanent residents live in the 201-km(2) core area of the city. METHOD: We used a generalized additive model to analyze pollution, mortality, and covariate data. The estimates of the interaction between high temperature and air pollution were obtained from the main effects and pollutant-temperature interaction models. RESULTS: We observed effects of consistently and statistically significant interactions between particulate matter < or = 10 microm (PM(10)) and temperature on daily nonaccidental (p = 0.014), cardiovascular (p = 0.007), and cardiopulmonary (p = 0.014) mortality. The PM(10) effects were strongest on extremely high-temperature days (daily average temperature, 33.1 degrees C), less strong on extremely low-temperature days (2.2 degrees C), and weakest on normal-temperature days (18.0 degrees C). The estimates of the mean percentage of change in daily mortality per 10-mug/m(3) increase in PM(10) concentrations at the average of lags 0 and 1 day during hot temperature were 2.20% (95% confidence interval), 0.74-3.68) for nonaccidental, 3.28% (1.24-5.37) for cardiovascular, 2.35% (-0.03 to 4.78) for stroke, 3.31% (-0.22 to 6.97) for cardiac, 1.15% (-3.54% to 6.07) for respiratory, and 3.02% (1.03-5.04) for cardiopulmonary mortality. CONCLUSIONS: We found synergistic effects of PM(10) and high temperatures on daily nonaccidental, cardiovascular, and cardiopulmonary mortality in Wuhan.