Isotopic Interpretation of Particulate Nitrate in the Metropolitan City of Karachi, Pakistan: Insight into the Oceanic Contribution to NOx.,Environmental Science & Technology

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Isotopic Interpretation of Particulate Nitrate in the Metropolitan City of Karachi, Pakistan: Insight into the Oceanic Contribution to NOx.
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2020-06-03 , DOI: 10.1021/acs.est.0c00490
Zheng Zong _{1,

2} , Chongguo Tian _{1,

2} , Jun Li ₃ , Jabir Hussain Syed ₄ , Wei Zhang ₅ , Yunting Fang ₆ , Yifan Jiang ₇ , Jawad Nasir ₈ , Muhammad Mansha ₈ , Syed Hussain Haider Rizvi ₈ , Muhammad Shafiq ₈ , Suhaib Bin Farhan ₈ , Gan Zhang ₃

Affiliation

CAS Key Laboratory of Coastal Environmental Processes and Ecological Remediation, Yantai Institute of Coastal Zone Research (YIC), Chinese Academy of Sciences (CAS), Shandong Key Laboratory of Coastal Environmental Processes, YICCAS, Yantai, Shandong 264003, P. R. China.
Center for Ocean Mega-Science, Chinese Academy of Sciences, No. 7, Nanhai Road, Qingdao City 266071, P. R. China.
State Key Laboratory of Organic Geochemistry and Guangdong Key Laboratory of Environmental Protection and Resources Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China.
Department of Meteorology, COMSATS University Islamabad (CUI), Park Road, Tarlai Kalan, Islamabad 45550, Pakistan.
School of Environmental and Material Engineering, Yantai University, Yantai, Shandong 264005, P. R. China.
CAS Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, Liaoning 110164, P. R. China.
Department of Civil and Environmental Engineering, National University of Singapore, Block E1A#07-03, No. 1 Engineering Drive 2, 117575 Singapore, Singapore.
Earth Sciences Directorate, Pakistan Space and Upper Atmosphere Research Commission (SUPARCO), P.O. Box 8402, Karachi 75270, Pakistan.

Nitrogen oxide (NO_x) abatement has become the focus of air quality management strategies. In this study, we examined NO_x sources and the atmospheric conversion of NO_x in Karachi, Pakistan, a megacity in South Asia with serious particulate pollution problems. Oceanic contributions to NO_x were quantified for the first time based on a novel approach using nitrogen/oxygen isotopic analysis in nitrate (δ¹⁵N–NO₃^–; δ¹⁸O–NO₃^–) and a Bayesian model. Our results showed that δ¹⁵N–NO₃^– in Karachi varied between −10.2‰ and +12.4‰. As indicated by the δ¹⁸O–NO₃^– findings (+66.2 ± 7.8‰), the •OH pathway dominated NO_x conversion throughout the nearly two-year observation, but high NO₃^– events were attributed to the O₃ pathway. Coal combustion was the most significant source (32.0 ± 9.8%) of NO_x in Karachi, with higher contributions in the autumn and winter; a similar situation occurred for biomass burning + lightning (30.3 ± 6.5%). However, mobile sources (25.2 ± 6.4%) and microbial processes (12.5 ± 7.5%) exhibited opposite seasonal trends. The oceanic contributions to NO_x in Karachi were estimated to be 16.8%, of which lightning, shipping emissions, and microbial processes accounted for 20.3%, 46.3%, and 33.4%, respectively, emphasizing the dominance of shipping emissions as an oceanic NO_x source.

中文翻译：

巴基斯坦首都卡拉奇大都会城市地区硝酸盐的同位素解释：海洋对NOx的贡献。

减少氮氧化物（NO _x）已成为空气质量管理策略的重点。在这项研究中，我们研究了NO _X光源和NO的转化大气_X在卡拉奇，巴基斯坦，南亚大城市严重的颗粒物污染问题。到NO海洋贡献_X用于使用硝酸盐氮/氧同位素分析基于一种新的方法在第一时间进行定量（δ ¹⁵ N-NO ₃^- ;δ ¹⁸ O型NO ₃^-）和贝叶斯模型。我们的研究结果表明，δ ¹⁵ N-NO ₃^-卡拉奇之间变化-10.2‰和+ 12.4‰。如δ所示¹⁸ O型NO ₃^-的调查结果（66.2±7.8‰），该•OH途径的主导NO _X转换贯穿近两年的观察，但高NO ₃^-事件归因于将O ₃途径。在卡拉奇，煤炭燃烧是NO _x的最主要来源（32.0±9.8％），在秋季和冬季贡献更大；生物质燃烧+闪电的情况类似（30.3±6.5％）。然而，流动源（25.2±6.4％）和微生物过程（12.5±7.5％）表现出相反的季节性趋势。海洋对NO _x的贡献在卡拉奇估计为16.8％，其中闪电，航运排放和微生物过程分别占20.3％，46.3％，和33.4％，，强调航运排放作为海洋NO的主导地位_X源。

更新日期：2020-07-07

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