Attributing Airborne Fungal Spore Increases to Wildfire in Southern California, USA

Abstract

Bioaerosols, particularly pollen and fungal spores, can trigger allergies, asthma, and other respiratory conditions. While warm, dry, and windy weather promotes their dispersal year-round, wildfires are an emerging and significant source of airborne bioaerosols. The intensity of wildfires, the dynamics of smoke plumes, soil disturbance during and after fires, and strong winds can increase the release and long-range transport of microorganisms. Recent studies show wildfire smoke contains higher concentrations and taxonomic diversity of viable microbes compared to non-smoke air. Understanding how wildfire smoke and wind-driven transport influence bioaerosol levels is critical to explaining the heightened toxicity of wildfire particulate matter. We use a novel two-stage interrupted time series analysis to quantify airborne fungal spore concentrations attributable to multiple wildfires using the Southern California firestorm during October 2007 as a case study. Our results suggest that elevated fungal spore counts during wildfire events are driven by both direct emissions and long-range transport via smoke plumes and winds, potentially spreading spores far beyond the burned areas. This mechanism may increase respiratory health risks in downwind communities that might otherwise have limited exposure to bioaerosols.