Spatial Heterogeneity of the Respiratory Health Impacts of Wildfire Smoke PM_2.5 in California

Abstract

Wildfire smoke fine particles (PM2.5) are a growing public health threat as wildfire events become more common and intense under climate change, especially in the Western United States. Studies assessing the association between wildfire PM2.5 exposure and health typically summarize the effects over the study area. However, health responses to wildfire PM2.5 may vary spatially. We evaluated spatially‐varying respiratory acute care utilization risks associated with short‐term exposure to wildfire PM2.5 and explored community characteristics possibly driving spatial heterogeneity. Using ensemble‐modeled daily wildfire PM2.5, we defined a wildfire smoke day to have wildfire‐specific PM2.5 concentration ≥15 μg/m3. We included daily respiratory emergency department visits and unplanned hospitalizations in 1,396 California ZIP Code Tabulation Areas (ZCTAs) and 15 census‐derived community characteristics. Employing a case‐crossover design and conditional logistic regression, we observed increased odds of respiratory acute care utilization on wildfire smoke days at the state level (odds ratio [OR] = 1.06, 95% confidence interval [CI]: 1.05, 1.07). Across air basins, ORs ranged from 0.88 to 1.57, with the highest effect estimate in San Diego. A within‐community matching design and spatial Bayesian hierarchical model also revealed spatial heterogeneity in ZCTA‐level rate differences. For example, communities with a higher percentage of Black or Pacific Islander residents had stronger wildfire PM2.5‐outcome relationships, while more air conditioning and tree canopy attenuated associations. We found an important heterogeneity in wildfire smoke‐related health impacts across air basins, counties, and ZCTAs, and we identified characteristics of vulnerable communities, providing evidence to guide policy development and resource allocation.

Using syndromic surveillance to rapidly assess the impact of a June 2023 wildfire smoke event on respiratory-related emergency department visits, Massachusetts, United States

“…While McArdle et al [3] did not stratify by race/ethnicity, other recent studies reported stronger associations between wildfire smoke PM 2.5 and respiratory acute care utilization among certain groups. Duncan et al [5] reported stronger associations among Black/African American residents in western North Carolina, and Do et al [24] in California communities with higher percentages of Black or Pacific Islander residents. Effects on communities that have historically experienced disproportionate exposure to environmental hazards and related health impacts, including those who are Black/African American and Hispanic/Latino, should continue to be considered as climate change is projected to exacerbate existing inequities [25,26].…”