Study on the measurement of deposition of small-sized droplets in the atmosphere

2002 Fiscal Year Final Research Report Summary

• Project/Area Number: 12680530
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Environmental dynamic analysis
• Research Institution: Toyo University
• Principal Investigator: IZUMI Katsuyuki Toyo University, Faculty of Engineering, Associate Professor, 工学部, 助教授 (70132842)
• Co-Investigator(Kenkyū-buntansha): FUKUYAMA Tsutomu PM2.5DEPResearch Project, National Inst. Environ. Studies, Research Team Leader, PM2・ 5・DEP研究プロジェクト・エアロゾル測定研究チーム, 総合研究官 (90011642) ; UTIYAMA Masahiro Atmospheric Environment Div., National Inst. Environ. Studies, Senior Researcher, 大気圏環境領域, 主任研究員 (20160294)
• Project Period (FY): 2000 – 2002
• Keywords: occult deposition / fog / deposition flux / super absorbent polymer / large-scale long vertical shaft

Research Abstract

It is known that fogs are more polluted and acidic than rain due to human activities, affecting ecosystems such as forest environments. However the amount of pollutants transported to forest trees associated with the deposition of fog droplets has been indirectly estimated through the measurement of 'through fall' and 'stem fall', caused by deposition of fog droplets, and there has been no direct measurement on this amount. In this study, we developed a method for the measurement of the deposition flux of fog water, Fw, with a polymeric water absorbent, by conducting basic experiments in a large-scale long vertical shaft in Kamaishi Mine, which afforded a steady fog. The deposition flux of a component, Fi, can be calculated through Fi=FwCi, where Ci is the concentration of the component in the droplet-phase. Based on this idea, we made field observations at Mt. Akagi in central Japan in the summer of 2002, to measure Fw and determine the concentrations of ionic species in collected fog water. In these experiments, artificial leaves imitating coniferous and deciduous leaves were prepared by cutting a sheet of a super absorbent polymer and exposed to fogs by hanging to trees around the site and a plastic coniferous tree imitating a Christmas tree. As a result, Fw values of the imitation leaves found to be larger at the windward side than the leeward side. Similar Fw values were obtained from the coniferous and deciduous leaves, hung to the shades of the trees. This suggests that the deposition flux is independent of the shape of leaves. On the other hand, the acidity of collected fog water was high, attaining pH=2.7. Dominant ionic species were H+, NH4+, SO42- and NO3-. However, H+ was not an important component when pH exceeded 4. The amounts of total deposition due to fog were 0.22, 0.07, 0.06 and 0.04 meq/m2 in a day, for H+, NH4+, SO42- and NO3- in September 5, when the concentrations of the aqueous species were highest. To evaluate the role of fogs in total deposition, long term observations are needed, in which the measurement of the deposition amount of acidic components associated with not only fogs but also rain is included.