Seasonal variation in health impacts associated with visibility in Beijing, China

Visibility has been continuously and stably observed for more than half a century, while particulate matter with an aerodynamic diameter ≤ 2.5 μm (PM_2.5) was not introduced to the national monitoring system in China until 2013. It is a scientific issue as to whether visibility can be used as an alternative to assess the health risks of air pollution in periods and areas without pollutant monitoring data. A generalized additive model (GAM) was adopted to estimate the impacts of seasonal changes in visibility on mortality in Beijing, China. Moreover, we estimated the contributions of particulate matter in the health effects of visibility by adjusting for dry extinction coefficient (β_dryext) and PM_2.5 in the model, respectively. We found that the acute health impacts of visibility varied by season, with the highest risks in winter. For respiratory mortality, the effect estimates per 1 km decrease in visibility were 0.40% (95% CI: 0.17-0.62%) in spring, 0.10% (95% CI: -0.14-0.34%) in summer, 0.27% (95% CI: 0.09-0.45%) in autumn, and 0.62% (95% CI: 0.38-0.85%) in winter. For cardiovascular mortality, the effect estimates per 1 km decrease in visibility were 0.20% (95% CI: 0.08-0.31%) in spring, 0.16% (95% CI: 0.04-0.27%) in summer, 0.25% (95% CI: 0.13-0.37%) in autumn, and 0.24% (95% CI: 0.13-0.35%) in winter. The seasonal pattern of health impacts related to visibility reflected the seasonal variations in the characteristics of air pollution emission sources and meteorological conditions that are unfavorable for pollutant dispersion. Particulate matter, particularly PM_2.5, made significant contributions to the health impacts of visibility. The results indicated that controlling pollutant emissions in winter would be of significant importance to improve air quality and mitigate the health hazard of air pollution in Beijing. Our study also provides further evidence on the feasibility of using visibility to assess the health impacts of particulate matter pollution.