Jiangxi Province Key Laboratory of the Causes and Control of Atmospheric Pollution, East China University of Technology, Nanchang, 330013, China; School of Water Resources and Environmental Engineering, East China University of Technology, Nanchang, 330013, China.
The State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081, China.
Environ Pollut. 2021 May 1;276:116708. doi: 10.1016/j.envpol.2021.116708. Epub 2021 Feb 8.
The determination of both stable nitrogen (δN-NO) and stable oxygen (δO-NO) isotopic signatures of nitrate in PM has shown potential for an approach of assessing the sources and oxidation pathways of atmospheric NOx (NO+NO). In the present study, daily PM samples were collected in the megacity of Beijing, China during the winter of 2017-2018, and this new approach was used to reveal the origin and oxidation pathways of atmospheric NOx. Specifically, the potential of field δN-NO signatures for determining the NOx oxidation chemistry was explored. Positive correlations between δO-NO and δN-NO were observed (with R between 0.51 and 0.66, p < 0.01), and the underlying environmental significance was discussed. The results showed that the pathway-specific contributions to NO formation were approximately 45.3% from the OH pathway, 46.5% from NO hydrolysis, and 8.2% from the NO+HC channel based on the δO-δN space of NO. The overall nitrogen isotopic fractionation factor (εN) from NOx to NO on a daily scale, under winter conditions, was approximately +16.1‰±1.8‰ (consistent with previous reports). Two independent approaches were used to simulate the daily and monthly ambient NOx mixtures (δN-NOx), respectively. Results indicated that the monthly mean values of δN-NOx compared well based on the two approaches, with values of -5.5‰ ± 2.6‰, -2.7‰ ± 1.9‰, and -3.2‰ ± 2.2‰ for November, December, and January (2017-2018), respectively. The uncertainty was in the order of 5%, 5‰ and 5.2‰ for the pathway-specific contributions, the εN, and δN-NOx, respectively. Results also indicated that vehicular exhaust was the key contributor to the wintertime atmospheric NOx in Beijing (2017-2018). Our advanced isotopic perspective will support the future assessment of the origin and oxidation of urban atmospheric NOx.
对 PM 中硝酸盐的稳定氮 (δN-NO) 和稳定氧 (δO-NO) 同位素特征的测定，为评估大气 NOx（NO+NO）的来源和氧化途径提供了一种方法。在本研究中，于 2017-2018 年冬季在中国特大城市北京采集了每日 PM 样本，并采用这种新方法揭示大气 NOx 的来源和氧化途径。具体而言，探讨了现场 δN-NO 特征在确定 NOx 氧化化学方面的潜力。观察到 δO-NO 与 δN-NO 之间存在正相关关系（相关系数 R 在 0.51 到 0.66 之间，p<0.01），并讨论了其潜在的环境意义。结果表明，基于 NO 的 δO-δN 空间，NO 形成的途径特异性贡献分别为 OH 途径约 45.3%、NO 水解约 46.5%和 NO+HC 通道约 8.2%。基于冬季条件，每日尺度上从 NOx 到 NO 的整体氮同位素分馏因子（εN）约为+16.1‰±1.8‰（与先前的报告一致）。分别采用两种独立的方法模拟每日和每月的环境 NOx 混合物（δN-NOx）。结果表明，两种方法得到的每月平均 δN-NOx 值之间具有很好的一致性，分别为-5.5‰±2.6‰、-2.7‰±1.9‰和-3.2‰±2.2‰，对应的月份为 2017-2018 年的 11 月、12 月和 1 月。途径特异性贡献、εN 和 δN-NOx 的不确定性分别在 5%、5‰和 5.2‰的量级。结果还表明，机动车尾气是北京（2017-2018 年）冬季大气 NOx 的主要贡献者。我们的先进同位素视角将支持未来对城市大气 NOx 来源和氧化的评估。
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