Marine Aerosol Composition And Its Potential Effect On CCN In The Southern Ocean

Marine aerosols have significant effects on global atmospheric physical and chemical processes.In the background of global warming,it is of great significance to investigate the composition,source and environmental behavior of Marine aerosols in the Southern Ocean.In this paper,the Marine aerosol in the Southern Ocean is taken as the research object.Based on China’s 34th Antarctic scientific expedition,the high resolution aerosol navigation observation technology is adopted,and the biological environmental factors such as wind speed,temperature,sea ice,colored dissolved organic matter（CDOM）and chlorophyll a（Chl-a）are combined.The high resolution distribution characteristics and influencing factors of biogenic aerosols and sea salt aerosols in the Southern Ocean were analyzed,and the transport effect of cyclones in the Southern Ocean on sea salt aerosols was explored.The nucleation characteristics of sea salt aerosol in different mixed states were analyzed by laboratory simulation experiments,and the effect of MSA on the nucleation of sea salt particles was studied.The main research conclusions are as follows:（1）The spatial distribution of Na⁺concentration in the 34th Antarctic expedition was consistent with that of the total aerosol,and there was a strong positive correlation between Na⁺and K⁺,Mg²⁺,Ca²⁺,Cl^-and SO₄^2-,indicating that sea salt particles dominated the aerosol in the Southern Ocean.（2）During the period of observation,spatial distributions of concentrations of dimethylsulfide（DMS）in the Southern Ocean differed greatly.Besides sea ice and precipitation,wind speed and Chl-a were positively correlated with DMS.However,there was no significant correlation between Chl-a and MSA,which may be due to the lag in the transformation relationship between Chl-a and MSA.There is a certain correlation between temperature and MSA,because low temperature can promote the conversion of DMS to MSA.It is worth noting that there is a good positive correlation between MSA and CDOM in the study.CDOM can strongly promote the photochemical oxidation of dissolved organic sulfur（DOS）in water and increase the production of MSA in the atmosphere.（3）Low wind speed（WS<7 m/s;Under the condition of 7≤WS<10 m/s）,there was almost no correlation between Na⁺concentration and temperature.But high wind speed（10≤WS<13 m/s;Under WS≥13 m/s）,Na⁺concentration showed a good correlation with temperature,which may be due to the fact that sea salt particles generated under high wind speed condition had larger particle size and strong gravity settlement compared with low wind speed condition.High temperature will accelerate the evaporation of water in sea salt particles and reduce gravity sedimentation,thus increasing the measured sea salt aerosol concentration.In addition,it is difficult for sea salt aerosols to absorb moisture under low relative humidity（RH<60%）,and sea salt particles generated under negative sea-temperature difference（SST-T<0）will have lower temperature and higher density than the surrounding air,so they tend to settle back to the sea surface.Both of these conditions are not conducive to the emission of sea salt aerosol.By comparing the changes of Na⁺concentration and particle size spectrum between cyclonic and non-cyclonic periods in the Southern Ocean,it was found that although the wind speed was stronger during cyclonic periods,the concentration of sea salt particles in the near-surface atmosphere did not rise significantly,which was mainly due to the low pressure caused by cyclones that might transport part of SSA upward.By comparing the difference of wind stress and sea salt flux between cyclonic and non-cyclonic periods,it is estimated that at least 27%of sea salt aerosols are transported to the sky during cyclonic periods.（4）Laboratory simulation results show that Na NO₃ has the highest nucleation efficiency,followed by Na₂SO₄,at a mass concentration of 10μg/m³ and 25μg/m³（particle size centered around 0.331μm）.The nucleation efficiency of Na Cl was the highest when the mass concentration was 1 mg/m³ and 2.5 mg/m³（particle size centered around 1.612μm）,while Na NO₃ and Na₂SO₄ had little change compared with before.Notably,nucleation efficiency of Na₂SO₄was about three times higher when mixed with MSA（10μg/m³,25μg/m³）.After mixing more MSA,the nucleation efficiency of Na₂SO₄was lower than before,but it was still higher than that of pure MSA particles and pure Na₂SO₄ particles.However,the nucleation efficiency of Na Cl and Na NO₃decreased after the addition of MSA.The results show that MSA can promote the nucleation of Na₂SO₄.Therefore,attention should be paid to the role of Na₂SO₄ in the nucleation of sea salt particles in the polar regions,especially the Antarctic region.