Effects of stress factors on biogenic isoprene emissions and their contribution to ozone and secondary organic aerosols in China.

Isoprene serves an important part in plant defense against biotic and abiotic stresses, while also exerting a crucial influence on atmospheric photochemical processes and global climate change. The regional climate-chemistry-ecosystem model (RegCM-Chem-YIBs) was employed in the following study to estimate the biogenic isoprene emissions (BISP) in China during 2018-2020. The model explored the relative contributions of various stress factors such as drought, carbon dioxide (CO2), and surface ozone (O3) to isoprene emissions. Furthermore, the potential effects of stress factors on surface O3 and secondary organic aerosol (SOA) were also assessed quantitatively. Investigations revealed that the three-year average BISP in China ranged between 15.38 and 22.23 Tg while considering different stress factors. BISP exhibited obvious seasonal variations, showing higher levels in summer and lower levels in winter, accounting for 55.4 % and 3.2 % of the annual total emissions, respectively. The effects of O3 damage and CO2 inhibition on BISP were found to be more significant as compared to drought stress. The CO2 suppression effect caused annual BISP across China to decrease about 10 %, whereas the largest reduction (-3 mg C m-2 d-1) appeared in southeastern China and eastern Sichuan. BISP in China decreased by about 16.3 % (6.8 %) at high (low) O3 damage sensitivity during 2018-2020. Variations in monthly emissions differed, with the largest decline in summer. If no stressors are considered, BISP leads to a maximum increase of 13 ppb in daily maximum 1 h (MDA1) O3 and 1.5 μg m-3 in SOA in summer. Under the combined effects of multiple factors (drought, CO2, and O3), the relative differences in O3 are over 50 % in central and eastern China, while the SOA formed by isoprene reduced by ~0.15 μgm-3 in China. The outcomes of this work emphasize the significance of multiple stressors on BISP and the resulting air quality.