Isoprene Emissions Response to Drought and the Impacts on Ozone and SOA in China

Among the various environmental factors that affect isoprene emissions, drought has only been given limited attention. Four different drought response (DR) schemes were implemented in the Model of Emissions of Gases and Aerosols from Nature (MEGAN, version 2.1), and the Community Multiscale Air Quality (CMAQ) model was applied to investigate the drought impacts on air quality during both drought and normal years in China. Generally, all DR schemes decrease isoprene emissions except for mild drought conditions. The significant decrease and even termination of isoprene emissions are predicted in South China under severe drought conditions. During the drought period, the DR scheme considering both mild and severe drought (SMD) improves the model performance especially in severe drought-hit regions when compared with the Ozone Monitoring Instrument (OMI) averaged formaldehyde vertical column density (HCHO VCD). The results show that most of the DR schemes decrease simulated ozone (O₃) and secondary organic aerosols (SOA) levels. For both O₃ and SOA, noticeable changes are predicted in the Sichuan Basin (5 ppb and 4 µg m⁻³ for O₃ and SOA, respectively). This investigation is the first modeling study to investigate the impacts of isoprene drought response on air quality in China.