Climate-pollution compound extremes drive PM2.5 beyond WHO air quality guidelines

Air pollution, heatwaves, droughts, and wildfires are increasingly interacting to create compound extremes that amplify risks to ecosystems, human health, and societal resilience. Yet, their global prevalence, intensity, and cascading impacts remain poorly quantified. Here, we provide a global assessment (2003–2022) of compound climate–pollution events, benchmarking outcomes against the World Health Organization (WHO) Air Quality Guideline (AQG) for fine particulate matter (PM2.5). Using a harmonized framework at 0.75° x 0.75° spatial resolution that integrates ERA5 reanalysis, CAMS PM2.5, and MODIS fire radiative power, we define compound events as the simultaneous co-occurrence of two or more hazards within the same grid-cell and day, map hotspots defined as grid-cells exceeding the 90 th percentile of yearly compound event frequency, quantify their frequencies, and evaluate the effect of compound events on fire intensity and pollution. We find that the co-occurrence of pollution with heatwaves, droughts, and fires is widespread, particularly across South America, Africa, Asia, boreal regions, and parts of Europe and Australia. During fire seasons, daily PM2.5 concentrations on compound heat–drought–fire–pollution (PHDF) days exceed pollution-only levels by more than 200% on average and up to 800% at the upper tail. These extremes consistently push air quality far beyond the WHO AQG, revealing a pronounced climate burden on clean air. Our findings highlight the global reach and intensity of compound climate–pollution events, emphasizing the urgent need for integrated strategies that jointly address air quality, wildfire risk, and adaptation to safeguard public health in a warming climate.