瀬戸内海沿岸部における大気エアロゾル中の有機態窒素

抄録

Chemical compositions and particle number densities of atmospheric aerosols were measured continuously in the coastal area of Seto Inland Sea during the spring of 2015. The mean concentrations of NH₄⁺, NO₃^-, and water soluble organic nitrogen (ON_ws) were 1.6, 0.85, and 0.28 μg N m^-3, respectively in total sampling mode. NO₃^- existed in both fine and coarse modes, while NH₄⁺ and ON_ws existed primarily in fine mode. On the days of normal atmospheric conditions, the amount of ON_ws contributing to the total nitrogen was about 14% N in both fine and coarse sampling modes. This ratio was equivalent to the amount of NO₃^- content in fine mode and NH₄⁺ in coarse mode. On the days with polluted atmospheric conditions, the amount of ON_ws contributing to total nitrogen was about 9.3% N in fine mode and about 5.0% N in coarse mode. This ratio was equivalent to the contributions of NO₃^- in fine mode and NH₄⁺ in coarse mode. Dry deposition fluxes of particulate NH₄⁺, NO₃^-, and ON_WS in the area were 280, 660, and 83 μg N m^-2 day^-1, respectively. The flux of NO₃^- was more effective than any other nitrogen compounds, since the deposition rate depends upon a size distribution. The dry deposition of ON_ws accounted for about 8.1% of the total nitrogen dry deposition. Thus, ON_WS cannot be ignored when considering the nitrogen budget and cycles in this area.