Cross-border pollution from China to Chugoku district estimated by sulfur and oxygen isotopic ratios of rain sulfate

2020 Fiscal Year Final Research Report

• Project/Area Number: 17K05716
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Geochemistry/Cosmochemistry
• Research Institution: Okayama University
• Principal Investigator: Chiba Hitoshi 岡山大学, 自然科学研究科, 特命教授 (30144736)
• Project Period (FY): 2017-04-01 – 2021-03-31
• Keywords: 降水硫酸 / 越境汚染 / 硫黄同位体比 / 酸素同位体比

Outline of Final Research Achievements

Monthly precipitations are collected for 4 years at 5 sampling stations which are located north-south from Tottori Prefecture at The Sea of Japan side to Okayama Prefecture at The Seto Inland Sea side. Their major chemistry and sulfur and oxygen isotopic composition of sulfate ion are analyzed. Seasonal variation of sulfur isotopic ratio of non-seasalt sulfate is high at winter season and low at summer season and is the same as the results obtained in other area in Japan. Seasonal variation of oxygen isotope ratio of non-seasalt sulfate, which is first analyzed in this study, is high at spring season and low in autumn season and is clearly different from the seasonal variation of sulfur isotope ratio. These two different seasonal variations indicate that yellow sand carried to Japan mainly at spring season is one of the source material of rain sulfate, which is not considered as a source material of rain sulfate before this study.

Free Research Field

無機地球科学

Academic Significance and Societal Importance of the Research Achievements

降水硫酸の酸素同位体比を初めて測定した。結果は硫黄同位体比と異なる春期に高く秋期に低い季節変動を示した。硫黄同位体比の冬期に高く夏期に低い季節変動と合わせて考察することにより，降水中の硫酸イオンには，これまで硫黄同位体比のみを用いた研究では考慮されていなかった黄砂が降水硫酸の重要な起源物質の一つであることが明らかになった。本研究の成果は，降水硫酸の起源物質の研究のみならず，浮遊粒子状物質（PM2.5やSPM）の水溶性物質に含まれている硫酸イオンの起源推定にも酸素同位体比が重要な指標となることを示している。