Undesirable Effects of Biogenic Emissions From Urban Green Spaces on Air Quality Are Counteracted by Their Transpiration and Dry Deposition

Urban green spaces (UGSs) are recognized beneficial for thermal comfort, yet its potential effects on air quality due to biogenic volatile organic compounds (BVOCs) emissions have received concerns. UGSs affect air quality through multiple pathways, some of which were generally missing in existing literature. Here we assess the impacts of UGSs on regional climate and air quality in the Pearl River Delta (PRD) with a more comprehensive framework. We consider the impacts of BVOCs emissions, dry deposition, radiative effects of produced aerosols, and transpiration effects. UGSs tend to elevate fine particulate matter (PM_2.5) concentrations by 5.11 μg/m³, dominated by evapotranspiration (4.62 μg/m³) that lowers mixing height and offset by additional dry deposition surfaces (−1.24 μg/m³). Although emitted BVOCs enhance ozone, evapotranspiration and dry deposition counterbalance the adverse effect by ∼87%. When considering the aerosol radiative effect, our findings indicate that both BVOC emissions and evapotranspiration contribute to mitigating the urban heat island effect between 14:00 and 16:00. Our results suggest that the air quality degradation will not be serious for cities with low aerosol concentrations if vegetations with less VOCs are planned. Additionally, UGSs can further help to alleviate urban warming.