Nitrate sources and formation of rainwater constrained by dual isotopes in Southeast Asia : example from Singapore
Emission of reactive nitrogen species has a major impact on atmospheric chemistry, ecosystem and human health. The origin and formation mechanisms of wet-deposited nitrate are not well understood in Southeast Asia (SEA). In this study, we measured stable isotopes of nitrate (δ15N and δ18O) and chemi...
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sg-ntu-dr.10356-1519232021-07-07T02:01:26Z Nitrate sources and formation of rainwater constrained by dual isotopes in Southeast Asia : example from Singapore Li, Cai Li, Si-Liang Yue, Fu-Jun He, Shaoneng Shi, Zong-Bo Di, Chong-Li Liu, Cong-Qiang Earth Observatory of Singapore Science::Geology Stable Isotopes Nitrate Formation Emission of reactive nitrogen species has a major impact on atmospheric chemistry, ecosystem and human health. The origin and formation mechanisms of wet-deposited nitrate are not well understood in Southeast Asia (SEA). In this study, we measured stable isotopes of nitrate (δ15N and δ18O) and chemical compositions of daily rainwater from May 2015 to July 2017 in Singapore. Our results showed that δ15N-NO3- and δ18O-NO3- varied seasonally with higher values during the Inter-monsoon period (April-May and October-November) than during Northeast (December-March) and Southwest monsoon (June-September). Bayesian mixing modeling, which took account of the isotope fractionation, indicated that traffic emission (47 ± 32%) and lightning (19 ± 20%) contributed the most to NO3- with increased traffic contribution (55 ± 37%) in the Northeast monsoon and lightning (24 ± 23%) during the Inter-monsoon period. Biomass burning and coal combustion, likely from transboundary transport, contributed ∼25% of nitrate in the rainwater. Monte Carlo simulation of δ18O-NO3- indicated that oxidation process by hydroxyl radical contributed 65 ± 14% of NO3-, with the rest from hydrolysis of N2O5. Wind speed had large effect on δ18O-NO3- variations in the atmosphere with more involvement of hydroxyl radical reactions when wind speed increased. Our study highlights the key role of isotopic fractionation in nitrate source apportionment, and the influence of meteorological conditions on nitrate formation processes in SEA. Ministry of Education (MOE) National Research Foundation (NRF) This work is financially supported by National Natural Science Foundation of China (Grant Nos. 41571130072 and 41861144026), National Key R&D Program of China (Grant No. 2016YFA0601002) and also the IAEA Coordinated Research Project (No. 2279/R0) as well as the National Research Foundation Singapore and the Singapore Ministry of Education under the Research Centres of Excellence initiative, which comprises Earth Observatory of Singapore contribution No.231. 2021-07-07T02:01:25Z 2021-07-07T02:01:25Z 2019 Journal Article Li, C., Li, S., Yue, F., He, S., Shi, Z., Di, C. & Liu, C. (2019). Nitrate sources and formation of rainwater constrained by dual isotopes in Southeast Asia : example from Singapore. Chemosphere, 241, 125024-. https://dx.doi.org/10.1016/j.chemosphere.2019.125024 0045-6535 https://hdl.handle.net/10356/151923 10.1016/j.chemosphere.2019.125024 31604191 2-s2.0-85072851021 241 125024 en Chemosphere © 2019 Elsevier Ltd. All rights reserved. |
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Science::Geology Stable Isotopes Nitrate Formation Li, Cai Li, Si-Liang Yue, Fu-Jun He, Shaoneng Shi, Zong-Bo Di, Chong-Li Liu, Cong-Qiang Nitrate sources and formation of rainwater constrained by dual isotopes in Southeast Asia : example from Singapore |
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Emission of reactive nitrogen species has a major impact on atmospheric chemistry, ecosystem and human health. The origin and formation mechanisms of wet-deposited nitrate are not well understood in Southeast Asia (SEA). In this study, we measured stable isotopes of nitrate (δ15N and δ18O) and chemical compositions of daily rainwater from May 2015 to July 2017 in Singapore. Our results showed that δ15N-NO3- and δ18O-NO3- varied seasonally with higher values during the Inter-monsoon period (April-May and October-November) than during Northeast (December-March) and Southwest monsoon (June-September). Bayesian mixing modeling, which took account of the isotope fractionation, indicated that traffic emission (47 ± 32%) and lightning (19 ± 20%) contributed the most to NO3- with increased traffic contribution (55 ± 37%) in the Northeast monsoon and lightning (24 ± 23%) during the Inter-monsoon period. Biomass burning and coal combustion, likely from transboundary transport, contributed ∼25% of nitrate in the rainwater. Monte Carlo simulation of δ18O-NO3- indicated that oxidation process by hydroxyl radical contributed 65 ± 14% of NO3-, with the rest from hydrolysis of N2O5. Wind speed had large effect on δ18O-NO3- variations in the atmosphere with more involvement of hydroxyl radical reactions when wind speed increased. Our study highlights the key role of isotopic fractionation in nitrate source apportionment, and the influence of meteorological conditions on nitrate formation processes in SEA. |
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Earth Observatory of Singapore |
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Earth Observatory of Singapore Li, Cai Li, Si-Liang Yue, Fu-Jun He, Shaoneng Shi, Zong-Bo Di, Chong-Li Liu, Cong-Qiang |
format |
Article |
author |
Li, Cai Li, Si-Liang Yue, Fu-Jun He, Shaoneng Shi, Zong-Bo Di, Chong-Li Liu, Cong-Qiang |
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Li, Cai |
title |
Nitrate sources and formation of rainwater constrained by dual isotopes in Southeast Asia : example from Singapore |
title_short |
Nitrate sources and formation of rainwater constrained by dual isotopes in Southeast Asia : example from Singapore |
title_full |
Nitrate sources and formation of rainwater constrained by dual isotopes in Southeast Asia : example from Singapore |
title_fullStr |
Nitrate sources and formation of rainwater constrained by dual isotopes in Southeast Asia : example from Singapore |
title_full_unstemmed |
Nitrate sources and formation of rainwater constrained by dual isotopes in Southeast Asia : example from Singapore |
title_sort |
nitrate sources and formation of rainwater constrained by dual isotopes in southeast asia : example from singapore |
publishDate |
2021 |
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https://hdl.handle.net/10356/151923 |
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1705151329682325504 |