Oxidation and sources of atmospheric NOx during winter in Beijing based on δ18O-δ15N space of particulate nitrate

Zhongyi Zhang; Hui Guan; Hongwei Xiao; Yue Liang; Nengjian Zheng; Li Luo; Cheng Liu; Xiaozhen Fang; Huayun Xiao

doi:10.1016/j.envpol.2021.116708

Oxidation and sources of atmospheric NOx during winter in Beijing based on δ¹⁸O-δ¹⁵N space of particulate nitrate

Environ Pollut. 2021 May 1:276:116708. doi: 10.1016/j.envpol.2021.116708. Epub 2021 Feb 8.

Authors

Zhongyi Zhang¹, Hui Guan², Hongwei Xiao³, Yue Liang³, Nengjian Zheng³, Li Luo³, Cheng Liu³, Xiaozhen Fang³, Huayun Xiao⁴

Affiliations

¹ 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.
² The State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081, China.
³ Jiangxi Province Key Laboratory of the Causes and Control of Atmospheric Pollution, East China University of Technology, Nanchang, 330013, China.
⁴ School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China. Electronic address: xiaohuayun@ecut.edu.cn.

PMID: 33609901
DOI: 10.1016/j.envpol.2021.116708

Abstract

The determination of both stable nitrogen (δ¹⁵N-NO₃^-) and stable oxygen (δ¹⁸O-NO₃^-) isotopic signatures of nitrate in PM_2.5 has shown potential for an approach of assessing the sources and oxidation pathways of atmospheric NOx (NO+NO₂). In the present study, daily PM_2.5 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 δ¹⁵N-NO₃^- signatures for determining the NOx oxidation chemistry was explored. Positive correlations between δ¹⁸O-NO₃^- and δ¹⁵N-NO₃^- were observed (with R² 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 NO₃^- formation were approximately 45.3% from the OH pathway, 46.5% from N₂O₅ hydrolysis, and 8.2% from the NO₃+HC channel based on the δ¹⁸O-δ¹⁵N space of NO₃^-. The overall nitrogen isotopic fractionation factor (εN) from NOx to NO₃^- 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 (δ¹⁵N-NOx), respectively. Results indicated that the monthly mean values of δ¹⁵N-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 δ¹⁵N-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.

Keywords: Beijing; Particulate nitrate; Vehicular exhaust; δ(18)O-δ(15)N space.

MeSH terms

Beijing
China
Environmental Monitoring*
Nitrates* / analysis
Nitrogen Isotopes / analysis
Nitrogen Oxides / analysis

Substances

Nitrates
Nitrogen Isotopes
Nitrogen Oxides