Differential Effects of Wildfire Smoke Fine Particulate Matter Exposure on Respiratory Disease Emergency Department Visits in the Western United States
Wenhao Wang, Linzi Li, Qingyang Zhu, Rohan R. D’Souza, Danlu Zhang, Haisu Zhang, Stefanie Ebelt, Howard H. Chang, Álvaro Alonso, Yang Liu
Abstract
Abstract Rationale Wildfires significantly affect air quality in the western United States. Although prior research has linked wildfire smoke fine particulate matter (i.e., aerodynamic diameter ≦2.5 μm [PM2.5]) to respiratory health outcomes, these studies typically have limited geographic and temporal coverage, lacking evidence from multiple states over extended periods. Objectives To examine the differential acute effects of wildfire smoke and nonsmoke PM2.5 exposure on respiratory disease emergency department visits in the western United States. Methods We obtained data on more than 6 million emergency department visits for respiratory diseases, including asthma, chronic obstructive pulmonary disease, upper respiratory infections (URIs), and bronchitis, from five states in the western United States during 2007–2018. Daily exposure to wildfire smoke and nonsmoke PM2.5 was estimated using a state-of-the-art model system. A time-stratified case cross-over design with conditional logistic regression models was used to assess the acute respiratory effects of smoke and nonsmoke PM2.5 exposure. Measurements and Main Results The odds ratios associated with a 1-μg/m³ increase in the 3-day average wildfire smoke PM2.5 were 1.016 (95% confidence interval, 1.015–1.016) for asthma, 1.004 (1.003–1.005) for chronic obstructive pulmonary disease, 1.001 (1.000–1.011) for URIs, and 1.004 (1.004–1.004) for bronchitis. Wildfire smoke PM2.5 had stronger estimated effects than nonsmoke PM2.5, particularly for asthma (nonsmoke PM2.5: odds ratio, 1.002; 95% confidence interval, 1.001–1.004). Stratified analyses showed greater vulnerability among women and adults. Sensitivity analyses confirmed robust associations across exposure windows, and concentration–response functions suggested no clear threshold for adverse effects. Conclusions Wildfire smoke PM2.5 was associated with increased risks of acute respiratory outcomes. Stronger effects were observed from smoke PM2.5 than nonsmoke PM2.5, particularly for asthma and URIs. These findings underscore the need for targeted public health interventions and further research into the unique toxicological properties of wildfire emissions.