Impact of air pollution waves on the burden of stroke in a megacity in China

Air pollution is associated with stroke, but few previous studies have explored the impact of exposure to a sustained high air pollution level (which we define as an air pollution wave) on stroke. We decomposed the effect estimates of air pollution waves into a main effect estimate and an added effect estimate. The main effect estimate was due to the absolute daily level of air pollution, and the added effect estimate was due to the duration of high-level air pollution. PM10, SO2, NO2 and the Air Pollution Index (API) were chosen as indictors to explore the comprehensive evaluation indictor. The generalized additive model was used to evaluate the impact of air pollution wave on years of life lost (YLLs) due to stroke in Tianjin, China, from 2006 to 2011. Finally, we adopted different air pollution wave definitions to explore features of the association. When using the API as an indicator of air pollution, the association between the air pollution wave and stroke YLLs were significantly increased. When the duration of persistent pollution became longer, the main effect estimate did not change much, but the added effect estimate continued to increase. When the duration was 3 days, the added effect estimate was a maximum of 36.47 years (95% CI: 6.46, 66.48), while the main effect estimate was only 27.87 years (95% CI: 7.62, 48.11). For the other air pollution indicators, the added effect estimate of PM10 were not statistically significant, whereas that of SO2 was significant. The mortality risk associated with the different indicators showed a similar pattern. The comparison results between different indicators suggest that API can better reflect impacts of air pollution waves. Sustained exposure to air pollution had main and added impacts on stroke. The government and public should attach importance to air pollution wave and take individual protection to reduce exposure to pollutants.