Does the early haze warning policy in Beijing reflect the associated health risks, even for slight haze?

Abstract

Visibility can be used as a highly relevant visual indicator of the air pollution level. Published data on the correlations between visibility and health outcomes are very limited in China, and the health effects of slight haze on the human body have not been clarified. A semi-parametric generalized additive model (GAM) was used to assess the acute health effects of visibility on respiratory–cardiovascular mortality in Beijing, China. The correlation between visibility and PM2.5 as well as the contributions of PM2.5 to the health effects of visibility were analysed. Stratification model was employed to investigate the health effects of slight haze. The mortality risk of impaired visibility on the current exposure day peaked and was statistically significant for all the mortality outcomes. Every 1 km decrease in visibility corresponded to a 0.78% (95% CI: 0.62–0.95%) increase in total respiratory mortality and 0.54% (95% CI: 0.45–0.61%) increase in total cardiovascular mortality. Older people (age ≥65) were at a higher risk than the younger age group under impaired visibility. PM2.5 had a negative logarithmic relationship relative to visibility. After adjustment for PM2.5, the risk estimates for both respiratory and cardiovascular mortality reduced. Short-term exposure to low visibility was significantly associated with increased respiratory and cardiovascular mortality in Beijing. The health risk of impaired visibility was particularly high, even in slight haze. The hazardous effects of visibility can be partially attributed to the effects of PM2.5. These results can provide useful reference for relevant agencies to determine whether an adjustment to the haze warning level is warranted. Our findings indicate that visibility can be used as an alternative indicator for air quality assessments if air pollution data are insufficient or not available, particularly in developing countries.