Effects of Multiple Wildfire Smoke Pollutants (PM _2.5 , PM ₁₀ , and Ozone) on Respiratory and Cardiovascular Hospitalizations in California (2006–2019)

The intensity and frequency of wildfire events in the United States are increasing, with wildfire emissions serving as a major contributor to air pollution, particularly through airborne particulate matter and ground-level ozone (O₃). Wildfire smoke detrimentally impacts human health, and evidence has shown that wildfire fine particulate matter (PM_2.5) might be more harmful than other sources of PM_2.5 for respiratory conditions. Epidemiological research on health effects of wildfire smoke has mainly focused on PM_2.5 and there is limited evidence on the impacts of particulate matter less than or equal to 10 μm in aerodynamic diameter (PM₁₀) and O₃. PM_2.5, PM₁₀, and O₃ might have differential effects on human health based on the source of emissions (smoke vs. non-smoke air pollution). Here, we first quantified the contribution of wildfires to PM₁₀ and O₃ concentrations in California, USA for years 2006-2019, using a statistical modeling framework. <i>R</i> ² for our PM₁₀ predictive model ranged between 0.68 and 0.78 for prediction using testing and all monitoring sites involved, respectively. Similarly, <i>R</i> ² values for our ozone predictive model ranged between 0.78 (hold-out sites) and 0.89 (all sites). Second, we quantified the short-term impacts of wildfire-specific PM₁₀ and O₃ concentrations, along with wildfire-specific PM_2.5, on hospital admissions for respiratory and cardiovascular illnesses during three different time periods and at various spatial extents (all California ZIP codes and regional analyses). We found heterogeneous effects of wildfire smoke pollutants on different health outcomes and across different regions and periods considered in our study.