Dry deposition outweighs BVOC chemistry in shaping vegetation-driven surface ozone responses across East Asia and the Indochina Peninsula.

Vegetation influences surface ozone (O3) through competing pathways, including biogenic volatile organic compound (BVOC)-related chemistry and dry-deposition removal. However, because BVOC-related chemistry and dry deposition respond simultaneously to vegetation change and can exert competing effects on O3, their relative contributions to the net surface O3 response remain insufficiently resolved across contrasting regional environments. Here, we assess leaf area index (LAI)-driven surface O3 responses across East Asia and the Indochina Peninsula during summer 2020, defined as June-August, when vegetation activity and biosphere-atmosphere exchange processes are generally most pronounced. We used the Community Multiscale Air Quality (CMAQ) model with default climatological LAI and satellite-derived LAI representative of 2020 conditions to evaluate the effects of updated vegetation information on surface O3. Component-specific sensitivity experiments were used to separate dry-deposition and BVOC-related responses, while additional stomatal sensitivity and reaction-rate diagnostics were used to resolve deposition and chemical-loss mechanisms. Updating LAI resulted in regional-mean surface O3 changes ranging from -1.23 to +1.29 ppb, with substantial country- and subdomain-level variability. In the northern part of the modeling domain, particularly North China, North Korea, and Mongolia, LAI increased by 19.85-46.55%, and surface O3 generally decreased, indicating that enhanced dry deposition dominated the comparatively small and regionally variable BVOC-related responses. In contrast, over the Indochina Peninsula, where LAI declined by 15.98-35.45%, surface O3 increased because of weakened depositional removal and reduced BVOC-related chemical O3 loss; the latter effect was most pronounced at night, with TERP-O3 reactions accounting for 74.61-84.86% of the summed contributions from the analyzed VOC-O3 loss reactions. Sensitivity-based attribution showed that surface O3 responses were controlled primarily by dry deposition, which accounted for 57.93-97.25% of the response, whereas BVOC-related processes contributed 2.75-42.07%. These results demonstrate that vegetation-driven O3 responses cannot be inferred from LAI changes or BVOC emission changes alone, but instead emerge from the balance among depositional removal, BVOC-mediated chemistry, and their region- and time-dependent responses. The process-resolved framework developed here highlights the need to account for these competing pathways when evaluating the air-quality consequences of vegetation change and vegetation-management strategies.