Wildfire smoke PM2.5 and mortality in the contiguous United States

Despite the substantial evidence on the health effects of short-term exposure to ambient fine particles (PM2.5), including increasing studies focusing on those from wildland fire smoke, the impacts of long-term wildland fire smoke PM2.5 exposure remain unclear. We investigated the association between long-term exposure to wildland fire smoke PM2.5 and non-accidental mortality and mortality from a wide range of specific causes in all 3,108 counties in the contiguous U.S., 2007-2020. Controlling for non-smoke PM2.5, air temperature, and unmeasured spatial and temporal confounders, we found a non-linear association between 12-month moving average concentration of smoke PM2.5 and monthly non-accidental mortality rate. Relative to a month with the long-term smoke PM2.5 exposure below 0.1 g/m3, non-accidental mortality increased by 0.16-0.63 and 2.11 deaths per 100,000 people per month when the 12-month moving average of PM2.5 concentration was of 0.1-5 and 5+ g/m3, 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 PM2.5 exposure. Smoke PM2.5 contributed to approximately 11,415 non-accidental deaths/year (95% CI: 6,754, 16,075) in the contiguous U.S. Higher smoke PM2.5-related increases in mortality rates were found for people aged 65 above. Positive interaction effects with extreme heat (monthly number of days with daily mean air temperature higher than the countys 90th percentile warm season air temperature) were also observed. Our study identified the detrimental effects of long-term exposure to wildland fire smoke PM2.5 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. Significance StatementThe area burned by wildland fire has greatly increased in the U.S. in recent decades. Short-term exposure to smoke pollutants emitted by wildland fires, particularly PM2.5, is associated with numerous adverse health effects. However, the impacts of long-term exposure to wildland fire smoke PM2.5 on health and specifically mortality remain unclear. Utilizing wildland fire smoke PM2.5 and mortality data in the contiguous U.S. during 2007-2020, we found positive associations between long-term smoke PM2.5 exposure and increased non-accidental, cardiovascular, ischemic heart disease, digestive, endocrine, diabetes, mental, and chronic kidney disease mortality rates. Each year, in addition to the well-recognized mortality burden from non-smoke PM2.5, smoke PM2.5 contributed to an estimated over 10 thousand non-accidental deaths in the U.S. This study demonstrates the detrimental effects of wildland fire smoke PM2.5 on a wide range of health outcomes, and calls for more effective public health actions and communications that span the health risks of both short- and long-term exposure.