中部山岳地域の降雪に含まれる化学成分濃度の空間分布

抄録

 The Japanese Alps region is one of the heaviest snowy regions in Japan. The aim of this study is to clarify the spatial distribution of chemical components in fresh snow, as well as the relationship between weather conditions and chemical characteristics of fresh snow in the Japanese Alps region. We conducted a snow pit study immediately after a snowfall on the route inland from Itoigawa city (N1) and Joetsu city (N2). We collected only fresh snow samples during the 2011/2012 winter season. The samples were melted and pH, electric conductivity, and major ions (Na⁺, K⁺, Mg²⁺, Ca²⁺, Cl^-, NO₃^-, and SO₄^2-) were analyzed in a clean room. The pH of all samples was below 5.62. Na⁺ concentration correlates well with Cl^- concentration. These ions are considered to be sea-salt components. These ions indicate the absence of chlorine loss. On the other hand, SO₄^2- concentrations included non-sea-salt components. Na⁺ and SO₄^2- concentrations decreased rapidly inland from the coastal area. The Na+ concentration of the N2 route was higher than that of the N1 route. It is considered that geomorphological features such as valley width and altitude differences influenced the transportation of chemical components. The chemical characteristics of the fresh snow layer changed with differences in weather conditions. Concentrations of sea-salt components were high in fresh snow when the vicinity of Japan was under the strong winter monsoon pattern. On the other hand, concentrations of sea-salt components were very low with snowfalls of plain snow. As a result of extracting the characteristic layer of Na⁺ concentration, changes in the vertical profiles of Na⁺ concentration became similar from the coast to the inland study sites. At the inland study sites, most SO₄^2- was of non-sea salt origin. We compared the depositions of Na⁺ and SO₄^2- in the fresh snow layer. Whereas there were large depositions of Na⁺ at the sampling sites near the sea, depositions of SO₄^2- increased inland. This is because non-sea salt components were carried inland more than sea salt components. At the inland sites, there was a layer of high NO₃^-/nssSO₄^2- component in the fresh snow. It is thought that the generation of NO₃^- by human activities near the site had an influence.