Long-term exposure to wildland fire smoke PM and mortality in the contiguous United States.

Despite the substantial evidence on the health effects of short-term exposure to ambient fine particles (PM), including increasing studies focusing on those from wildland fire smoke, the impacts of long-term wildland fire smoke PM exposure remain unclear. We investigated the association between long-term exposure to wildland fire smoke PM and nonaccidental mortality and mortality from a wide range of specific causes in all 3,108 counties in the contiguous United States, 2007 to 2020. Controlling for nonsmoke PM, air temperature, and unmeasured spatial and temporal confounders, we found a nonlinear association between 12-mo moving average concentration of smoke PM and monthly nonaccidental mortality rate. Relative to a month with the long-term smoke PM exposure below 0.1 μg/m, nonaccidental mortality increased by 0.16 to 0.63 and 2.11 deaths per 100,000 people per month when the 12-mo moving average of PM concentration was of 0.1 to 5 and 5+ μg/m, respectively. Cardiovascular, ischemic heart disease, digestive, endocrine, diabetes, mental, and chronic kidney disease mortality were all found to be associated with long-term wildland fire smoke PM exposure. Smoke PM contributed to approximately 11,415 nonaccidental deaths/y (95% CI: 6,754, 16,075) in the contiguous United States. Higher smoke PM-related increases in mortality rates were found for people aged 65 and above. Positive interaction effects with extreme heat were also observed. Our study identified the detrimental effects of long-term exposure to wildland fire smoke PM on a wide range of mortality outcomes, underscoring the need for public health actions and communications that span the health risks of both short- and long-term exposure.