Environment/Climate Change
Wildfire smoke PM2.5 and mortality rate in the contiguous United States: a causal modeling study Yaguang Wei* Yaguang Wei Min Zhang Edgar Castro Alexandra Shtein Adjani A. Peralta Mahdieh Danesh Yazdi Xiao Wu Joel D. Schwartz
Background: Smoke PM2.5 has emerged as a significant environmental hazard in the US, driven by increasing wildfire activities due to climate change. However, the causal relationship between chronic exposure to smoke PM2.5 and mortality remains particularly scarce.
Methods: The annual all-cause mortality for 3068 counties in the contiguous US, along with cause-specific death records for circulatory diseases, nervous diseases, neoplasms, respiratory diseases, endocrine, nutritional and metabolic diseases, and mental and behavioral disorders, were collected from US Centers for Disease Control and Prevention from 2006 to 2020. Concentrations of smoke PM2.5 were estimated using spatio-temporal models at a 10 km2 resolution. We used a doubly robust method, incorporating flexible generalized propensity score estimation strategies while relaxing the distributional assumption for exposure, to estimate additive effects of annual exposure to smoke PM2.5 on mortality. Transport accident mortality was used as a negative outcome control to test the assumption of no unmeasured confounding.
Results: Each 0.1-unit increase in smoke PM2.5 was associated with increased all-cause mortality rate (rate difference: 1.904, 95% CI: 1.620 to 2.188 per 100,000 persons) and increased mortality for all cause-specific outcomes, with nervous diseases being most susceptible. This translated to approximately 5,594 attributable all-cause deaths per year. The exposure-response curve for all-cause mortality showed no evidence of “safe” threshold. There was no evidence of the association between smoke PM2.5 and the negative outcome control. Effects were greater in communities with a higher percentage of population under 65 years old, in more rural areas, and during periods of lower temperatures in summer and winter.
Conclusions: Our study provided robust evidence for the chronic effect of smoke PM2.5 on mortality, underscoring the urgent need to mitigate the escalating burden of wildfires.
