Short-term effects of fine and coarse particles on deaths in Hong Kong elderly population: An analysis of mortality displacement.

Background: While numerous studies worldwide have evaluated the short-term associations of fine and coarse particulate matter (PM) air pollution with mortality and morbidity, these studies may be susceptible to short-term harvesting effect. We aimed to investigate the short-term association between mortality and PM with aerodynamic diameter less than 2.5 μm (PM) and those between 2.5 and 10 μm (PMc) within a month prior to death, and assess the mortality displacement by PM and PMc among elderly population in Hong Kong.

Methods: We obtained air pollution data from January 2011 to December 2015 from Environmental Protection Department, and daily cause-specific mortality data from Census and Statistical Department of Hong Kong. We performed generalized additive distributed lag model to examine the acute, delayed and long-lasting effects of PM and PMc within one month on mortality.

Results: We observed a statistically significant association of PM and PMc exposure over lags 0-6 days with all natural mortality and cardio-respiratory mortality. The overall cumulative effect of PM over 0-30 lag days was 3.44% (95% CI: 0.30-6.67%) increase in all natural mortality and 6.90% (95% CI: 0.58-13.61%) increase of circulatory mortality, which suggested the absence of mortality displacement by PM. On the other hand, no significant cumulative association with mortality was found for PMc over 0-30 lag exposure window, and thus mortality displacement by PMc cannot be ruled out. Findings remained robust in various sensitivity analyses.

Conclusions: We found adverse effect of both PM and PMc exposure within one week prior to death. While there was no evidence of mortality displacement in the association of PM exposure over one month prior with all natural and circulatory mortality, mortality displacement by PMc cannot be ruled out. PM may contribute more to the longer term effect of particulate matter than PMc.