Chemical characterization of sub-micron aerosols over the East Sea (Sea of Japan).

Studies of the land-sea-air interactions of aerosol are scarce considering their significant role in global environmental changes. Here, we investigated potential sources of sub-micron aerosols over the East Sea (Sea of Japan), which is strongly influenced by continental and marine aerosols. A high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was used to measure the size-resolved chemical compositions of sub-micron aerosols during the period March 10-15, 2020. Concentrations of all AMS species, black carbon (BC), PM (particulate matter <10 μm) and PM (particulate matter <2.5 μm) were higher when cruising in industrialized coastal areas compared to the offshore region. A positive matrix factorization (PMF) model identified five distinct sources, i.e., hydrocarbon-like organic aerosol, semi-volatile and low-volatile oxygenated aerosols, methanesulfonic acid (MSA), and dimethyl sulfide (DMS; CHS) oxidation, which accounted for 5.98 %, 21.6 %, 28.3 %, 34.5 %, and 9.64 % of the total organic mass, respectively. The spatiotemporal variation of MSA, as well as the MSA to sulfate ratio (MSA:SO) over the East Sea, was determined for the first time. The mass concentrations of MSA displayed a similar time series distribution pattern to those of DMS. The time series distributions of the MSA:SO ratio displayed distinct differences, with higher ratios downwind of the ocean (0.216 ± 0.083 μg·m) than land (0.089 ± 0.030 μg·m). The growth of ultrafine particles (10-35 nm) was observed during two of the elevated MSA:SO ratio events, suggesting a potential role of MSA in new particle formation.