A model assessment of the relationship between urban greening and ozone air quality in China: a study of three metropolitan regions.

The impact of biogenic emissions on ozone (O) has significant implications for air quality management. We analyze biogenic volatile organic compound (BVOC) emissions resulting from urban greening in three major Chinese cities, and impacts on tropospheric ozone. Urban greening BVOCs contributed 1.9 ppb (2.5%), 1.9 ppb (3.3%), and 3.6 ppb (5.9%) to O formation in Beijing, Shanghai, and Guangzhou, respectively. Temperature-driven enhancement in urban BVOCs produces significantly enhanced O on hot days. Guangzhou shows the highest summer temperatures, and the impact of the BVOC isoprene on O is more significant. The urban BVOC contribution to O is concentrated downwind of each city, due to transport processes. Estimated O-related mortality in the cities was 900-2000 people during summertime, with 6-14% of the O-related deaths attributable to urban BVOC emissions. The potential contribution of urban isoprene-emitting vegetation to air quality should be considered alongside the potential benefits of urban greening in future policy-making decisions.