Impacts of climate-driven vegetation changes on air quality over East Asia: Modulation of biogenic VOC emissions and secondary pollutants.

Climate change is reshaping terrestrial ecosystems across East Asia, driving substantial shifts in leaf area index (LAI) and vegetation productivity. These changes in vegetation activity directly affect biogenic volatile organic compound (BVOC) emissions, which in turn influence secondary air pollutants such as ozone (O3) and biogenic secondary organic aerosols (BSOA). We quantify the impact of LAI variability on regional air quality using the WRF-Chem model coupled with the MEGAN biogenic emissions module. We conducted two simulations for August 2024: a baseline case using default 2003 LAI fields and a sensitivity case incorporating updated satellite-derived LAI for 2024. Satellite observations reveal regionally heterogeneous greening trends across East Asia over the past two decades, driven by climatic and land-use changes. Model results show that LAI variations modulate BVOC emissions, and these emission changes propagate to BSOA and O3 responses depending on local chemical regimes. By combining model simulations with satellite-derived formaldehyde-to-nitrogen dioxide ratios, we find that the strongest BSOA and O3 responses occur in suburban transition zones where both vegetation changes and chemical conditions favor BVOC oxidation. In contrast, NOx-saturated megacities experience weaker responses due to suppressed chemical efficiency and smaller vegetation changes, whereas NOx-limited regions show muted changes despite substantial vegetation increases because insufficient NOx constrains O3 and aerosol production. These results highlight that dynamic vegetation processes significantly influence air quality in East Asia. Incorporating realistic vegetation conditions into emission inventories and chemical transport models will enhance predictability and support more effective air quality management under ongoing climate and ecosystem change.