Impact of Transported Wildfire Emissions on Urban PM _2.5 and O ₃ in Queensland, Australia

Abstract

Wildfires degrade urban air quality by transporting fine particulate matter () and ozone () precursors. Such impacts are seldom quantified in the Southern Hemisphere. This study quantified contributions of wildfire emissions to ambient and ( and ) across 22 urban monitoring sites in Queensland, Australia, in 2008–2023, using a counterfactual machine learning model. Wildfire‐impacted hours during fire‐active seasons (July–December) were approximately three times more frequent in 2018–2023 than 2008–2017. During wildfire‐impacted periods of the fire‐active seasons, the relative enhancement of and due to wildfire emissions reached 160.5% and 33.2% at maximum, respectively. The was controlled by the wildfire intensities and their atmospheric transport time. ‐ ratio was used to indicate the interaction between wildfire emissions and local emissions. Daytime increased monotonically with higher ‐ ratios, indicating a stronger influence of wildfire emissions.