The Interaction between Ambient PM and NO₂ on Mortality in Guangzhou, China.

Air pollution is now a significant environmental issue in China. To better understand the health impacts of ambient air pollution, this study investigated the potential interaction between PM and NO₂ on mortality in Guangzhou, China. Time series data of daily non-accidental mortality and concentrations of PM and NO₂ from 2006 to 2010 were collected. Based on generalized additive model, we developed two models (bivariate model and stratified model) to explore the interaction both qualitatively and quantitatively. At lag of 0-2 days, greater interactive effects between PM and NO₂ were presented in the graphs. Positive modified effects were also found between the two pollutants on total non-accidental death and cardiovascular death. When the NO₂ concentration was at a high level (>76.14 μg/m³), PM showed the greatest excess relative risk percentage (ERR%) for total non-accidental mortality (0.46, 95% CI: 0.13-0.79) and cardiovascular disease mortality (0.61, 95% CI: 0.06-1.16) for each 10 μg/m³ increase. During the period of high PM concentration (>89.82 μg/m³), NO₂ demonstrated its strongest effect for total non-accidental mortality (ERR%: 0.92, 95% CI: 0.42-1.42) and cardiovascular disease mortality (ERR%: 1.20, 95% CI: 0.38-2.03). Our results suggest a positive interaction between PM and NO₂ on non-accidental mortality in Guangzhou.