Chemical characteristics of cloud water over the Japan Sea and the Northwestern Pacific Ocean near the central part of Japan: airborne measurements

Cloud water was collected by aircraft over the Japan Sea and the Northwestern Pacific Ocean during the winter and early spring seasons. The concentrations of major ions in the cloud water were higher at cloud bases than at cloud tops. The equivalents based ratio of Na+/nssSO42− and NO3−/nssSO42− at cloud bases was higher than that at cloud tops, whereas the nssCa2+/nssSO42− ratio was higher at cloud tops. The concentrations of nssSO42− were higher than those of NO3− over the Japan Sea. The ratio of NO3−/nssSO42− in the cloud water over the Pacific Ocean was higher than that over the Japan Sea. Especially, when the winter monsoon wind pressure pattern collapsed, the concentrations of NO3− were much higher than those of nssSO42−. The concentrations of peroxides in the cloud water ranged from below the detection limit to 6.2 μM, and were much lower than those in the fog water near the summit of Mt. Norikura during the summer season. Most of the samples showed the condition (NH4++nssCa2+)<(NO3−+nssSO42−), which implies insufficient amounts of bases to neutralize the acids. Chloride loss in the cloud water was observed, and this may be caused by the deposition of HCl gas to the sea surface.