2022 Fiscal Year Final Research Report

New developments in environmental geochemistry, pioneered by isotopic fractionation associated with the evaporation of elements of different volatilities.

Research Project

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Project/Area Number	18H04134
Research Category	Grant-in-Aid for Scientific Research (A)
Allocation Type	Single-year Grants
Section	一般
Review Section	Medium-sized Section 63:Environmental analyses and evaluation and related fields
Research Institution	The University of Tokyo
Principal Investigator	Takahashi Yoshio 東京大学, 大学院理学系研究科(理学部), 教授 (10304396)
Co-Investigator(Kenkyū-buntansha)	板井啓明東京大学, 大学院理学系研究科(理学部), 准教授 (60554467) 足立光司気象庁気象研究所, 全球大気海洋研究部, 主任研究官 (90630814)
Project Period (FY)	2018-04-01 – 2022-03-31
Keywords	XAFS / TEM / 同位体分別 / エアロゾル / 放射線セシウム / Fe / 酸化チタン微粒子
Outline of Final Research Achievements	In this study, systematic understanding of degree of isotope fractionation during evaporation processes for Fe, Zn, and Cd isotopes in aerosol samples was obtained due to the difference in their volatilities. We have also obtained their chemical species to obtain information of their sources and chemical processes. In particular, Fe isotope ratio was fractionated to a largest degree due to its low evaporation rate, by which we can estimate anthropogenic emission component of Fe in aerosols based on the degree of the Fe isotope fractionation. Its application to marine aerosols revealed that 20-50% of soluble Fe in the marine aerosols in the North Pacific is of anthropogenic origin. Similar studies were extended to Fe and Zn in volcanic aerosols, which also exhibited lighter isotope ratios compared with the crustal values, which infer the volcanic origin of these elements especially in the pre-industrial era with much lower ratio of anthropogenic evaporated components in the atmosphere.
Free Research Field	地球化学、環境化学、大気化学、エアロゾル化学
Academic Significance and Societal Importance of the Research Achievements	同位体比を用いたエアロゾル中の人為起源鉄の割合推定から、人為起源鉄が海洋の植物プランクトンの活動をより活発化させ、その結果、大気中CO2濃度の増加が実際の値より少なくとも数％は抑制されていることが示され、これは確度の高い地球温暖化予測において重要である。Zn同位体比と化学種の解析から、大気中のZnがガソリン起源、石炭起源、天然起源の3成分の混合で説明可能であることが分かり、その結果、石炭起源成分のZnの割合が2003年以降減少傾向にあることが分かった。また産業革命以前であれば、FeとZnの同位体比から火山起源成分の割合が推定可能であることが分かった。