Assessing the impact of shipping emissions on ozone concentrations in East Asia: Insights from KORUS-AQ and SIJAQ 2021 campaign periods

This study analyzed the impact of shipping emissions on ozone (O3) concentrations in East Asia during the KoreaUnited States Air Quality (KORUS-AQ) and the Satellite Integrated Joint monitoring for Air Quality (SIJAQ) 2021 campaign period. Numerical simulations were performed during the KORUS-AQ (May 2016, the KORUS case) and the SIJAQ 2021 (October-November 2021, the SIJAQ case) using Community Multi-scale Air Quality (CMAQ), the three-dimensional chemical transport model. We additionally simulated an experiment without shipping emissions to compare the impact with and without shipping emissions. Using the validated simulation results, the average O3 concentrations in inland regions were found to be 35.63 ppb and 20.62 ppb in the KORUS and SIJAQ cases, respectively. The average O3 concentrations were higher in the KORUS case owing to the difference in weather conditions between the two cases in various seasons. The results of examining the impact of shipping emissions on O3 concentrations in the ocean area indicate that both the KORUS and SIJAQ cases resulted in a decrease in O3 concentrations in the Yellow Sea region, while the O3 concentrations increased in the East Sea and North Pacific regions. In particular, in the Yellow Sea and East China Sea, where the O3 concentrations decreased in the KORUS case, O3 sensitivity results showed volatile organic compounds (VOC)-sensitive regime when the shipping emissions were removed but changed to nitrogen oxide (NOx)-sensitive regime when the shipping emissions were added. Meanwhile, in the inland regions, the SIJAQ case decreased O3 concentrations in most areas, whereas the KORUS case showed an increase in O3 concentrations in the Korean Peninsula and Japan. Analysis of O3 sensitivity revealed that the regions of the Korean Peninsula and Japan, where O3 concentrations increased, exhibited a NOx-sensitive regime. Particularly, in the case of the Korean Peninsula, the initial transport of shipping emissions in the western part led to a decrease in O3 concentrations. However, as shipping emissions were further transported from west to east, they became more diluted, and additional NOx generated by O3 titration reactions was also transported, gradually increasing O3 concentrations. Furthermore, we found that during seasons with abundant BVOC emissions, the transport of shipping emissions could contribute to additional O3 production. These results confirmed that shipping emissions in East Asia primarily reduce O3 concentrations, however, differences in seasonal and regional O3 sensitivity and transportation patterns can contribute to O3 production.