Ozone and daily mortality in Shanghai, China

BACKGROUND: Controversy remains regarding the relationship between ambient ozone and mortality worldwide. In mainland China, the largest developing country, there has been no prior study investigating the acute effect of O-3 on death risk. Given the changes in types of air pollution from conventional coal combustion to the mixed coal combustion/motor vehicle emissions in China's large cities, it is worthwhile to investigate the acute effect of O-3 on mortality outcomes in the country. OBJECTIVES: We conducted a time-series study to investigate the relation between O-3 and daily mortality in Shanghai using 4 years of daily data (2001-2004). METHODS: We used the generalized additive model with penalized splines to analyze mortality, O-3 pollution, and covariate data in warm and cold seasons. We considered daily counts of all-cause mortality and several causc-specific subcategories (respiratory and cardiovascular). We also examined these associations among several subpopulations based on age and sex. RESULTS: O-3 was significantly associated with total and cardiovascular mortality in the cold season but not in the warm season. In the whole-year analysis, an increase of 10 pg/m(3) of 2-day average (lag01) O-3 corresponds to 0.45% [95% confidence interval (CI), 0.16-0.73%], 0.53% (95% CI, 0.10-0.96%), and 0.35% (95% CI, -0.40 to 1.09%) increase of total nonaccidental, cardiovascular, and respiratory mortality, respectively. In the cold season, the estimates increased to 1.38% (95% CI , 0.68-2.07%), 1.53% (95% CI ,0.54-2.52%), and 0.95% (95% CI, -0.71 to 2.60%), respectively. In the warm season, we did not observe significant associations for both total and causespecific mortality. The results were generally insensitive to model specifications such as lag structure of O-3 concentrations and degree of freedom for time trend. Multipoflutant models indicate that the effect of O-3 was not confounded by particulate matter <= 10 mu m in diameter (PM10) or by sulfur dioxide; however, after adding nitrogen dioxide into the model, the association of O-3 with total and cardiovascular mortality became statistically insignificant. CONCLUSIONS: O-3 pollution has stronger health effects in the cold than in the warm season in Shanghai. Our analyses also.strengthen the rationale for further limiting levels of O-3 pollution in outdoor air in the city.