A time-stratified case-crossover study of fine particulate matter air pollution and mortality in Guangzhou, China

Few studies in China investigate health impact of fine particulate matter (PM2.5) due to lack of monitoring data and the findings are controversial. The aim of this study is to examine the short-association between PM2.5 and daily mortality in Guangzhou, the economic center of south China. In Guangzhou, we measured daily PM2.5 concentrations between 2007 and 2008 and conducted a time-stratified case-crossover analysis to explore the association between PM2.5 and daily mortality, and examine potential effect modifiers including age, sex, and education. The averaged PM2.5 concentration in 2007-2008 was 70.1 mu g/m(3) in Guangzhou, which was approximately seven times higher than the WHO Air Quality Guidelines for PM2.5 (annual average: 10 mu g/m(3)). Regression analysis showed that ambient PM2.5 was associated with mortality from all causes and cardiorespiratory diseases. An increase of 10 mu g/m(3) in 2-day moving average (lag01) concentration of PM2.5 corresponds to 0.90% [95% confidence interval (CI): 0.55, 1.26%] increase of total mortality, 1.22% (95% CI: 0.63, 1.68%) increase of cardiovascular mortality, and 0.97% (95% CI: 0.16, 1.79%) increase of respiratory mortality. The associations were stronger in the elderly (aged 65 years or more), in females, and in those with low education level, but the differences were statistically insignificant. After adjustment for nitrogen dioxide (NO2), however, the effects of PM2.5 decreased and became statistically insignificant. Our findings provided new information for the adverse health effects of PM2.5 in China, and may have some implications for environmental policy making and standard setting in Guangzhou.