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Abstract 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 O₃and SOA, noticeable changes are predicted in the Sichuan Basin (5 ppb and 4 µg m⁻³for O₃and SOA, respectively). This investigation is the first modeling study to investigate the impacts of isoprene drought response on air quality in China. 

Abstract. Biogenic volatile organic compounds (BVOCs) are important components of the atmosphere due to their contribution to atmospheric chemistry and biogeochemical cycles. Tropical forests are the largest source of the dominant BVOC emissions (e.g. isoprene and monoterpenes). In this study, we report isoprene and total monoterpene flux measurements with a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) using the eddy covariance (EC) method at the Tapajós National Forest (2.857∘ S, 54.959∘ W), a primary rainforest in eastern Amazonia. Measurements were carried out from 1 to 16 June 2014, during the wet-to-dry transition season. During the measurement period, the measured daytime (06:00–18:00 LT) average isoprene mixing ratios and fluxes were 1.15±0.60 ppb and 0.55±0.71 mg C m−2 h−1, respectively, whereas the measured daytime average total monoterpene mixing ratios and fluxes were 0.14±0.10 ppb and 0.20±0.25 mg C m−2 h−1, respectively. Midday (10:00–14:00 LT) average isoprene and total monoterpene mixing ratios were 1.70±0.49 and 0.24±0.05 ppb, respectively, whereas midday average isoprene and monoterpene fluxes were 1.24±0.68 and 0.46±0.22 mg C m−2 h−1, respectively. Isoprene and total monoterpene emissions in Tapajós were correlated with ambient temperature and solar radiation. Significant correlation with sensible heat flux, SHF (r2=0.77), was also observed. Measured isoprene and monoterpene fluxes were strongly correlated with each other (r2=0.93). The MEGAN2.1 (Model of Emissions of Gases and Aerosols from Nature version 2.1) model could simulate most of the observed diurnal variations (r2=0.7 to 0.8) but declined a little later in the evening for both isoprene and total monoterpene fluxes. The results also demonstrate the importance of site-specific vegetation emission factors (EFs) for accurately simulating BVOC fluxes in regional and global BVOC emission models.