Wildfire Smoke PM2.5 and Mortality in Contiguous United States

Key Takeaways

• Annual wildfire-smoke PM2.5 exposure was associated with a substantial all-cause mortality burden across the contiguous United States.
• Mortality rates increased for all studied outcomes except transport accidents and falls, which served as negative outcome controls.
• All-cause mortality rose monotonically without evidence of a safe threshold, and neurological disease mortality showed the largest increase among cause-specific outcomes.

Across the contiguous United States from 2006 through 2020, annual wildfire-smoke PM2.5 exposure was estimated to be responsible for about 24,100 all-cause deaths per year. In Wildfire Smoke PM2.5 and Mortality in Contiguous United States, investigators examined whether chronic annual smoke exposure tracked with mortality across the country in a national ecological analysis. The estimate focused on annual wildfire-related fine particulate exposure across communities rather than on individual patients. The findings supported a chronic effect of wildfire-smoke PM2.5 on mortality across this nationwide population-level comparison.

Researchers evaluated annual wildfire-smoke PM2.5 exposure against all-cause and six cause-specific mortality outcomes in the contiguous United States during 2006 to 2020. The study used a doubly robust method with flexible generalized propensity score estimation, a framework central to its causal-modeling design. This approach allowed for potential nonlinearity and confounder interactions while relaxing the assumed distribution form for exposure. It estimated annual smoke exposure in relation to multiple mortality endpoints within one national framework. The analysis assessed population-level mortality associations across the contiguous United States in a national ecological comparison.

Mortality rates were higher for every studied outcome except transport accidents and falls, which served as negative outcome controls. That pattern was seen in the overall mortality measure and the six cause-specific outcomes included in the model. The two null outcomes provided an internal comparison against endpoints not expected to follow the same pattern. Among the six cause-specific outcomes, neurological disease mortality showed the largest increase per 0.1 μg/m3 increase in wildfire-smoke PM2.5 exposure. Overall, elevated mortality outcomes were reported alongside null results in the designated negative controls.

The all-cause curve in the wildfire-smoke PM2.5 exposure-response analysis rose monotonically as annual exposure increased. Investigators also found no evidence of a safe threshold for all-cause mortality within the observed exposure range. The authors said the study provided robust evidence for chronic effects of wildfire-smoke PM2.5 on mortality and underscored an urgent need for targeted measures to mitigate the burden of wildfires. Together, the estimated national mortality burden and monotonic curve described a persistent pattern across increasing annual wildfire-smoke PM2.5 levels.