Long-term exposure to smoke PM2.5 and COPD caused mortality for elderly people in the contiguous United States

Wildfire events in the US are becoming more frequent and more intensive due to climate change. Fire smoke can significantly contribute to ambient PM_2.5 (PM_2.5, particles smaller than 2.5 µm in diameter) levels and alter its chemical composition. An emerging body of literature has linked COPD mortality and episodic wildfire smoke exposure, but studies on the effect of long-term fire smoke exposure is lacking. We aimed to evaluate how long-term exposure to smoke PM_2.5 can affect COPD mortality among elderly people and to explore the spatial variability in this effect. We investigated all elderly people aged 65-100 years in the contiguous United States using Medicare and National Death Index data from 2008 to 2016. We identified three subregions based on wildfire smoke risk to indicate spatial differences in smoke exposure. We used time-varying Cox Proportional Hazards Models to explore the effect of smoke PM_2.5 on COPD mortality. We found that smoke PM_2.5 is strongly associated with COPD mortality. An increase of 1 µg/m³ in smoke PM_2.5 was associated with a 9.2 % increase in COPD mortality among elderly people (95 % CI: 8.8 %-9.7 %). Specifically, A 1 µg/m³ increase in smoke PM_2.5 may increase deaths by 40.4 %, 9.6 % and 3.9 % in low, moderate, and high wildfire risk areas, respectively. Our study reveals that long-term exposure to smoke PM_2.5 significantly contributes to COPD mortality among elderly people. Notably, those living in regions with relatively lower wildfire risk appear vulnerable. Therefore, wildfire prevention should be emphasized in areas that are not typically wildfire active.