Differential Effects of Wildfire Smoke Pm2.5 Exposure on Respiratory Disease Emergency Department Visits in the Western United States

Background: Wildfires significantly affect air quality in the Western United States. Although prior research has linked wildfire smoke PM2.5 to respiratory health outcomes, these studies typically have limited geographic and temporal coverage, lacking evidence from multiple states over extended periods. Methods: We obtained data on over 6 million emergency department (ED) visits for respiratory diseases, including asthma, chronic obstructive pulmonary disease (COPD), upper respiratory infections (URI), and bronchitis, from five states in the Western US during 2007-2018. Daily exposure to wildfire smoke and non-smoke PM2.5 was estimated using a state-of-the-art model system. A time-stratified case-crossover design with conditional logistic regression models was used to assess the acute respiratory effects of smoke and non-smoke PM2.5 exposure. Findings: The odds ratios associated with a 1 µg/m3 increase in the 3-day average wildfire smoke PM2.5 were 1.016 (1.015-1.016) for asthma, 1.004 (1.003–1.005) for COPD, 1.001 (1.000–1.011) for upper respiratory infections (URI), and 1.004 (1.004–1.004) for bronchitis. Wildfire smoke PM2.5 had stronger estimated effects than non-smoke PM2.5, particularly for asthma (non-smoke PM2.5: OR 1.002, 1.001–1.004). Stratified analyses showed greater vulnerability among women and adults. Sensitivity analyses confirmed robust associations across exposure windows, while concentration-response functions suggested no clear threshold for adverse effects. Conclusion: Wildfire smoke PM2.5 was associated with elevated risks of acute respiratory outcomes. Stronger effects were observed from smoke PM2.5 than non-smoke PM2.5, particularly for asthma and upper respiratory infections. These findings underscore the need for targeted public health interventions and further research into the unique toxicological properties of wildfire emissions.