Modeling Biogenic Volatile Organic Compounds Emissions and Subsequent Impacts on Ozone Air Quality in the Sichuan Basin, Southwestern China

Biogenic volatile organic compounds (BVOCs) impact atmospheric oxidation capacity and regional air quality through various biogeochemistry processes. Accurate estimation of BVOC emissions is crucial for modeling the fate and transport of air pollutants in chemical transport models. Previous modeling characterizes the spatial variability of BVOCs while estimated BVOC emissions show large uncertainties, and the impacts of BVOC emissions on ozone (O-3) air quality are not well understood. In this study, we estimate the BVOC emissions by model of emissions of gases and aerosols from nature (MEGAN) v2.1 and MEGAN v3.1 over the Sichuan Basin (SCB) situated in southwestern China for 2017. Further, the critical role of BVOC emissions on regional O-3 pollution is illustrated with a CMAQ modeled O-3 episode in summer 2017. Annual BVOC emissions over the SCB in 2017 are estimated to be 1.8 x 10(6) tons with isoprene emissions as high as 7.3 x 10(5) tons. Abundant BVOC emissions are depicted over the southern and southeastern SCB, in contrast to the relatively low emissions of BVOC over the Chengdu Plain and northeastern SCB. CMAQ simulations depict a strong influence of BVOC on ambient O-3 formation over densely forested regions including southern SCB and Chongqing city, accounting for 10% of daily maximum hourly O-3 concentration (DM1h O-3) and 6% of daily maximum 8-h average O-3 (MDA8h O-3) concentrations in July 2017. Over the severe O-3 episode in summer 2017, sensitivity experiments indicate that enhanced BVOC emissions contribute substantially to basin-wide O-3 concentrations and elevate peak O-3 levels by 36.5 and 31.2 mu g/m(3) for the southern SCB and Chengdu Plain, respectively. This work identifies robustly important effects of BVOC emissions on O-3 exceedance events over the SCB and contributes insight into pursuing an O-3 abatement strategy with full consideration of potential contributions from BVOC emissions.