The mechanism of the formation of high sulfate concentrations over the Yellow Sea during the KORUS-AQ period: The effect of transport/atmospheric chemistry and ocean emissions

Abstract

This study investigates the chemical properties of high-concentration sulfate (SO42−) that appeared on the surface of the Yellow Sea during the KORUS-AQ period (April–June 2016). For quantitative analysis, we carry out numerical simulation using the Community Multi-scale Air Quality (CMAQ) model for the KORUS-AQ period (the BASE case) and another simulation of ocean emissions (the OCEAN case) that determines the effect of including ocean emissions on the results of the analysis. CMAQ-simulated (the BASE case) sulfate (SO42−), nitrate (NO3−), ammonium (NH4+), elemental carbon (EC), and organic carbon (OC) show high concentrations of these constituents centering around eastern China, the Liaodong Peninsula, and the western inland area of the Korean Peninsula. SO42−, unlike the other particulate matter constituents, shows high concentrations (up to 14.44 μg/m3) at the surface of the Yellow Sea. Results of the Integrated Process Rate (IPR) analysis show that the chemical production of SO42− over the Yellow Sea can primarily be attributed to the “aerosol process”, which is mainly dependent on weather conditions (e.g., temperature and wind speed) and concentrations of precursors such as SO2 and OH. The results of the analysis of the mechanism of SO42− formation using the Sulfur Tracking Model (STM) show that most chemical SO42− production (79.12%) on the surface of the Yellow Sea is the result of the aqueous-phase chemical reactions following the SO2 oxidation reaction (OH + SO2 → H2SO4 + HO2). Comparing the results of the OCEAN and BASE cases, we find that the primary mechanism of SO42− formation over the Yellow Sea shows no significant change with regard to ocean emissions. These results also confirm that increases in SO42− concentrations (up to 4.79 μg/m3) on the surface of the sea are not proportional to the distribution and amounts of ocean emissions, and in some areas, concentrations could decrease (up to −2.65 μg/m3) as a result of complex non-linear chemical reactions.