Despite the growing evidence on the health effects of wildfire smoke in the western U.S., the nationwide mortality risk and burden attributable to wildfire smoke fine particles (PM2.5) remain unclear. This study aims to investigate the association between wildfire smoke PM2.5 and mortality from all causes, cardiovascular diseases, respiratory diseases, and mental disorders, and calculate the corresponding attributable mortality burden in all 3,108 counties in the contiguous U.S., from 2006 to 2016. Monthly county-level mortality counts were collected from National Center for Health Statistics. Wildfire smoke PM2.5 concentration was derived from a 10×10 km2 resolution spatiotemporal model. Controlling for non-smoke PM2.5, air temperature, and unmeasured spatial and temporal confounders, we found that a 1 μg/m3 increase in smoke PM2.5 was significantly associated with an increase of 0.14% (95% confidence interval [CI]: 0.11%, 0.17%) in all-cause mortality, 0.13% (95% CI: 0.08%, 0.18%) in cardiovascular mortality, 0.16% (95% CI: 0.07%, 0.25%) in respiratory mortality, and 1.08% (95% CI: 0.93%, 1.23%) in mental disorder mortality. Smoke PM2.5 contributed to approximately 1,141 all-cause deaths/year (95% CI: 893, 1,388) in the contiguous U.S., of which over three-fourths were from cardiovascular, respiratory, and mental causes. We found a higher vulnerability among males than females, people aged 0 to 64 years than those ≥65 years, and racial/ethnic minorities than non-Hispanic White people. Mild droughts were found to enhance the association between smoke PM2.5 and mortality. Our results indicate that wildfire smoke PM2.5 harms both physical and mental health, which suggests the need for more effective wildfire mitigation strategies and public health responses in the U.S.

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Background: The average concentration of fine particulate matter (PM2.5) has decreased in the U.S. in recent years. However, the health benefits of this improvement among different racial/ethnic groups are not known. This study aimed to estimate the associations between long-term exposure to ambient PM2.5 and cause-specific cardiovascular disease (CVD) mortality rate and assess the PM2.5-attributable CVD deaths in non-Hispanic White, non-Hispanic Black, and Hispanic people across all counties in the contiguous U.S. from 2001 to 2016. Methods: Using nationwide CVD mortality data for all ages obtained from National Center for Health Statistics, this study applied interactive fixed effects models to estimate the associations between 12-month moving average of PM2.5 concentrations and monthly age-adjusted CVD mortality rates by race/ethnicity, controlling for both measured and unmeasured spatiotemporal confounders. Mortality from major types of CVD (ischemic heart disease [IHD], myocardial infarction [MI], stroke, hypertensive disease, and hypertensive heart disease) was also studied. We then calculated the burden of PM2.5-attributable CVD deaths in different race/ethnicity groups and examined the magnitude of racial/ethnic disparity and its changes over time. Results: A total of 13,289,147 CVD deaths were included in the study. Each 1-μg/m3 increase in 12-month moving average of PM2.5 concentration was associated with increases of 7.16 (95% confidence interval [CI]: 3.81, 10.51) CVD deaths per 1,000,000 Black people per month, significantly higher than the estimates for non-Hispanic White people (P value: 0.002). The higher vulnerability in non-Hispanic Black people was also observed for mortality from IHD, MI, and stroke. Long-term PM2.5 exposure contributed to approximately 75.47 (95% CI: 40.14, 110.80) CVD deaths per 1,000,000 non-Hispanic Black people annually, over 3 times higher than the estimated rate in non-Hispanic White people (16.89, 95% CI:13.17, 20.62). From 2001 to 2016, the difference in attributable CVD mortality rate between Black and White people reduced by 44.04% (from 75.80 to 42.42 per 1,000,000 people), but the burden in Black people was still over 3 times higher compared to White people. Conclusions: Non-Hispanic Black people have the highest PM2.5-attributable CVD mortality burden. Although the racial/ethnic disparity in this burden was narrowed over time, the gap between racial/ethnic minorities and non-Hispanic White people remains substantial.