The observation of isotopic compositions of atmospheric nitrate in Shanghai China and its implication for reactive nitrogen chemistry
The observation of isotopic compositions of atmospheric nitrate in Shanghai China and its implication for reactive nitrogen chemistry
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上海大气硝酸盐同位素组成观测及其对活性氮化学的意义
DOI：
10.1016/j.scitotenv.2020.136727
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发表时间：
2020
影响因子：
9.8
通讯作者：
Yue Fange
中科院分区：
文献类型：
--
作者：
He Pengzhen;Xie Zhouqing;Yu Xiawei;Wang Longquan;Kang Hui;Yue Fange
我国PM2.5污染的发生通常与大气中氮氧化物（NOX= NO + NO2）的氧化产物硝酸盐的形成有关。硝酸盐的氧-17过量（Δ 17 O（NO3−））可以用来揭示硝酸盐形成途径的相对重要性，并更深入地了解活性氮化学。本文介绍了2016年1 - 6月在中国上海收集的大气硝酸盐（Δ 17 O和δ 15 N）同位素组成的观测结果。大气中硝酸盐的浓度范围为1.4至24.1微克m− 3，平均值为（7.6 ± 4.4（1SD）），（10.2 ± 5.8）和（4.1 ± 2.4）μg m− 3，Δ 17 O（NO3−）变化范围为20.5‰ ~ 31.9‰，平均值为冬季为（26.9 ± 2.8）‰，其次为春季为（26.6 ± 1.7）‰，最低（23.2 ± 1.6）‰.Δ 17 O（NO3−）约束的估算表明，NO2+ OH和/或NO2+ H2O是NO2--N转化为NO3--N的主要途径，平均可能贡献率为55-77%，夏季甚至更高（84-92%）。在昼夜采样期间，Δ 17 O（NO3-）的日变化特征为白天高（28.6 ± 1.2‰），夜间低（25.4 ± 2.8‰）。这一趋势与硝酸盐的大气寿命（τ）有关，计算表明，在昼夜采样期间，τ约为15小时。δ 15 N（NO3-）变化较大，从-2.9 ‰到18.1‰，平均为（6.4 ± 4.4）‰。相关性分析表明，δ 15 N（NO3−）的变化是NOx排放源和同位素分馏过程共同作用的结果。在未来的研究中，我们的观察与模式模拟的帮助下，将进一步提高对城市地区活性氮化学的理解。
The occurrence of PM2.5pollution in China is usually associated with the formation of atmospheric nitrate, the oxidation product of nitrogen oxides (NOX= NO + NO2). The oxygen-17 excess of nitrate (Δ17O(NO3−)) can be used to reveal the relative importance of nitrate formation pathways and get more insight into reactive nitrogen chemistry. Here we present the observation of isotopic composition of atmospheric nitrate (Δ17O andδ15N) collected from January to June 2016 in Shanghai China. Concentrations of atmospheric nitrate ranged from 1.4 to 24.1 μg m−3with the mean values being (7.6 ± 4.4 (1SD)), (10.2 ± 5.8) and (4.1 ± 2.4) μg m−3in winter, spring and summer respectively.Δ17O(NO3−) varied from 20.5‰ to 31.9‰ with the mean value being (26.9 ± 2.8) ‰ in winter, followed by (26.6 ± 1.7) ‰ in spring and the lowest (23.2 ± 1.6) ‰ in summer.Δ17O(NO3−)-constrained estimates suggest that the conversion of NOXto nitrate is dominated by NO2+ OH and/or NO2+ H2O, with the mean possible contribution of 55–77% in total and even higher (84–92%) in summer. A diurnal variation ofΔ17O(NO3−) featured by high values at daytime (28.6 ± 1.2‰) and low values (25.4 ± 2.8‰) at nighttime was observed during our diurnal sampling period. This trend is related to the atmospheric life of nitrate (τ) and calculations indicate τ is around 15 h during the diurnal sampling period. In terms ofδ15N(NO3−), it changed largely in our observation, from −2.9‰ to 18.1‰ with a mean of (6.4 ± 4.4) ‰. Correlation analysis implies that the combined effect of NOXemission sources and isotopic fractionation processes are responsible forδ15N(NO3−) variations. Our observations with the aid of model simulation in future study will further improve the understanding of reactive nitrogen chemistry in urban regions.