Spatio-temporal Distribution Characteristics And Source Of Water-soluble Inorganic Ions In Marine Aerosols Over The Northwest Pacific Ocean And The Coastal Waters Of The East China Sea

With the rapid development of industry, massive sulfate and nitrate aerosols produced by human activity with dust aerosols are transported to the coastal waters and open ocean. Dust storm derived from northwest Asian and polluted aerosols came from East Asia had directly influenced on marine aerosol compositions over the northwest Pacific Ocean,which made this sea area a significant area on marine aerosol research. We collected marine aerosol samples over the northwestern Pacific Ocean in summer and autumn for two years, including the aerosol samples on two simultaneous cruises over the northwestern Pacific Ocean and the eastern China coastal waters in the same autumn in 2014.The 9 major water-soluble ions, Na+、Cl-、Mg2+、K+、NH4+、Ca2+、MSA、NO3-、SO₄^2- were analyzed for the samples. The results show that the sea-salt compositions（Na+、Cl- etc.） had a higher proportion of total water-soluble ions than the secondary aerosols(NO3-、nss-SO₄^2-、NH4+) over the northwestern Pacific Ocean. However, the seasonal differences of water-soluble ions between summer and autumn in this study was not significant, but secondary aerosols had a smaller proportion of total water-soluble ions in autumn than in summer. On the other hand, there were a significant variations of water-soluble ions constitute between northwestern Pacific Ocean and the eastern China coastal waters. Driven by the continental air mass, the concentration of secondary aerosols in eastern China coastal waters were higher than those of northwestern Pacific Ocean, leading to a higher proportion in total water-soluble ions.Moreover, the seasonal discrepancies of water-soluble ions source over northwestern Pacific Ocean was not obvious. In summer and autumn, Na+、Cl-、Mg2+ came mainly from the sea-salt, and K+、Ca2+、SO₄^2- were both derived from sea-salt and non-sea-salt source, which sea-salt was the major source for them. Polluted aerosol was the dominating origin of NH4+ and NO3-. Structure of water-soluble ions sources was obviously different between northwest Pacific Ocean and eastern China coastal waters. The result suggested that K+、Ca2+、SO₄^2- originated primarily from non-sea-salt source over eastern China coastal waters, which indicate that continental air mass had a great influence on marine aerosol in this sea area.The concentration of MSA were analyzed for all samples, and result showed that the concentrations of MSA in summer surpassed those in autumn. No obvious variations was observed in the MSA distribution. However, the contribution of biogenic-sulfate to total nss-sulfate had a remarkable spatial-temporal differences. The ratio of biogenic-sulfate to total non-sea-salt sulfate in summer and autumn over the northwest Pacific Ocean was 19.6% and 85.5% respectively, and 7.8% in autumn over the eastern China coastal waters. The ratio of biogenic-sulfate to the total non-sea-salt sulfate in autumn was higher than summer, and higher over northwestern Pacific Ocean than eastern coastal China.In this study, we also estimated the dry deposition fluxes of NH4+,NO3- and nss-SO₄^2-,which were 2.1、71.9、14.6 mg·m-2·month-1 in summer and 0.5、26.0、3.2 mg·m-2·month-1 in autumn over northwestern Pacific Ocean respectively and 7.0、225.3 、 31.0 mg·m-2·month-1 in autumn over eastern China coastal waters.The continental air masses had profound impacts on the dry deposition flux of nutrient aerosol.