Environment/Climate Change
Long-term exposure to wildfire smoke and mortality: differences in effects by exposure metric and vulnerable populations Lara Schwarz* Lara Schwarz Chen Chen Timothy B. Frankland Sara Y. Tartof Gina S. Lee Yuqian M. Gu Elizabeth Rose Mayeda David González Tarik Benmarhnia Joan A. Casey
Wildfire smoke was once a rare event but has become a repeated exposure globally. Evidence to demonstrate the acute health effects of wildfire particulate matter (PM2.5) is growing, yet little is known about its long-term effects. Using a cohort of Kaiser Permanente Southern California (KPSC) members aged ≥60, we estimate the association between three-year exposure to five different census tract-level wildfire smoke metrics (mean daily wildfire-specific PM2.5, mean daily wildfire-specific PM2.5 during the peak wildfire week, number of days with daily wildfire-specific PM2.5 above zero, number of weeks with average wildfire-specific PM2.5 above five, and number of smoke wave days) and all-cause mortality, and evaluate differences by individual and community-level socio-demographics. We apply a discrete-time approach with a pooled logistic regression, adjusting for age, sex, race and ethnicity, marital status, smoking status, calendar year, requiring an interpreter and census tract-level poverty and population density. Of the 1,250,083 KPSC members aged ≥60 included in the study population, 53% were women, and most identified as non-Hispanic White (49%) or Hispanic (26%). When comparing those highly exposed (95th percentile) to those minimally exposed (5th percentile), we find an increased odds of mortality for those highly exposed across all five wildfire smoke metrics. Results suggest that mean daily wildfire PM2.5 may be the most harmful smoke metric [odds ratio (OR): 1.073, 95% CI: 1.052, 1.093]. Those aged 60 to 65, those who identified in the Black or Other race or ethnic group or those who lived in a census tract with higher poverty appear to be more vulnerable to the long-term effects of smoke. Understanding what long-term wildfire smoke exposure is most harmful and what populations are most at risk will help us understand biological mechanisms and inform effective adaptation strategies to limit exposure and protect population health and health equity.
