Vegetation‐Atmosphere Feedbacks Exacerbate Ozone Pollution During Compound Heatwave and Drought in the Northern Hemisphere

Abstract Abnormally elevated ozone (O 3 ) is observed during compound heatwave and drought (CHWD), posing severe environmental and socioeconomic threats. Response of O 3 to CHWD is complicated by the vegetation‐atmosphere feedbacks through influencing biogenic emissions and stomatal deposition. Here, we employed a regional meteorology‐chemistry‐vegetation coupled model, integrated with optimized drought emission algorithm and interactive dry deposition scheme, to investigate the vegetation‐atmosphere feedbacks and their effects on O 3 pollution during CHWD. Analysis shows that CHWD have intensified in the northern hemisphere, with more frequent occurrence, stronger intensity and longer duration compared to the average climatology. Unusually elevated O 3 levels and exceedance frequency by more than 20% compared to normal conditions were observed during CHWD in the United States, western Europe and China. Model results indicate that heatwaves and droughts jointly lead to 10%–24% increase of summertime biogenic volatile organic compound emissions in vegetated regions, except in the severely drought‐affected areas. Furthermore, extremely hot and dry conditions induce stomatal closure and suppress plant growth, inhibiting O 3 stomatal removal by water‐stressed vegetation. It is estimated that such intricate vegetation‐atmosphere feedbacks substantially exacerbate O 3 pollution during CHWD, with equal importance to that of increased photochemical rates. Our findings offer a novel perspective on the interactions between climate, vegetation, and chemistry regarding compound extreme weather events.