Chemical characteristics of wintertime aerosol and cloud over the Sea of Japan based on aircraft and ground measurements

Chemical characteristics of aerosols and clouds from the boundary layer to the middle troposphere (0-5.2 km) were investigated over the Sea of Japan during winter seasons and were shown to be influenced by the Asian winter monsoon blowing from Siberia. The Na+/Cl- ratio of aerosols and clouds indicates that most Na+ and Cl- originated from sea salts. Positive correlations were found between sea spray aerosol production flux and (Na+ + Cl-) concentrations of boundary layer aerosols (R-2 = 0.53-0.71) or clouds (R-2 = 0.45-0.69), suggesting that strong winter monsoon winds intensified the production of primary sea salts and the associated clouds. The degree of Cl loss for aerosols near ground level was higher than that at high altitudes, which may be attributed to the distance from emission sources, whereas clouds were scarcely accompanied by Cl loss. The higher (NO3- + non-sea salt (nss)-SO42-)/(NH4+ + nss-Ca2+) ratio of aerosols in the boundary layer compared with the free troposphere may be attributed to the effect of relative humidity on acid gases (SO2, H2SO4, and HNO3) uptake to aerosols. The (NO3- + nss-SO42-)/(NH4+ + nss-Ca2+) ratio of clouds (0.67 on average) implies insufficient amounts of base ions to neutralize acid ions. The Se(VI)/Se(IV) ratios of aerosols in the boundary layer were mostly higher than those of the free troposphere, which may be attributed to the concentrations of oxidants for selenium in aerosol particles. The Se(IV)/Se(VI) ratios of clouds (1.34 +/- 0.62) were found to differ significantly from those of aerosols (0.50 +/- 0.32 for the boundary layer, 27.92 +/- 52.42 for the free troposphere), which strongly suggests that the oxidation state of Se in cloud indicates redox equilibrium.