Huang Weijie, Ye Xingnan, Lv Zhixiao, Yao Yinghui, Chen Yanan, Zhou Yuanqiao, Chen Jianmin
Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention (LAP3), National Observations and Research Station for Wetland Ecosystems of the Yangtze Estuary, Department of Environmental Science and Engineering, Fudan University, Shanghai 200438, China.
Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention (LAP3), National Observations and Research Station for Wetland Ecosystems of the Yangtze Estuary, Department of Environmental Science and Engineering, Fudan University, Shanghai 200438, China; Institute of Eco-Chongming (IEC), Chongming District, Shanghai 202162, China.
Sci Total Environ. 2024 Jun 25;931:172918. doi: 10.1016/j.scitotenv.2024.172918. Epub 2024 Apr 30.
The source apportionment and main formation pathway of nitrate aerosols in China are not yet fully understood. In this study, PM samples were collected in Shanghai in the summer and winter of 2019. Water-soluble inorganic ions and isotopic signatures of stable nitrogen (δN-NO) and stable oxygen (δO-NO) in PM were determined. The results showed that NO was less important in summer (NO/SO = 0.4 ± 0.8), while it became the dominant species in winter (52.1 %). The average values of δN-NO and δO-NO in summer were + 2.0 ± 6.1 ‰ and 63.3 ± 9.4 ‰ respectively, which were significantly lower than those in winter (+7.2 ± 3.4 ‰ and 88.3 ± 12.1 ‰), indicating discrepancies between NOx sources and nitrate formation pathways. Both δN-NO and δO-NO were elevated at night, demonstrating that NO hydrolysis contributed to the nocturnal nitrate increase even in summer. The contribution of the OH oxidation pathway to nitrate aerosols averaged at 70.5 ± 17.0 % in summer and NO hydrolysis dominated the nitrate production in winter (approximately 80 %). On average, vehicle exhaust, coal combustion, natural gas burning, and soil emission contributed 50.7 %, 21.5 %, 15.9 %, and 11.9 %, respectively, to nitrate aerosols in summer, and contributed 56.8 %, 23.9 %, 13.6 %, and 5.7 %, respectively, to nitrate production in winter. Notably, natural gas burning is a non-negligible source of nitrate aerosols in Shanghai. In contrast to an inverse correlation between δN-NO and PM, the value of δO-NO was positively correlated with nitrate concentration and aerosol liquid water content (ALWC) in winter, suggesting that explosive growth of nitrate was driven by continuous accumulation of N-depleted NOx and rapid NO hydrolysis under calm and humid conditions. To continuously improve air quality, priority control should be given to vehicle emissions as the dominant source of NOx and volatile organic compounds (VOCs) in Shanghai.
中国硝酸盐气溶胶的来源解析和主要形成途径尚未完全明确。本研究于2019年夏季和冬季在上海采集了PM样本。测定了PM中水溶性无机离子以及稳定氮（δN-NO）和稳定氧（δO-NO）的同位素特征。结果表明，NO在夏季的重要性较低（NO/SO = 0.4 ± 0.8），而在冬季成为主要成分（52.1%）。夏季δN-NO和δO-NO的平均值分别为+2.0 ± 6.1‰和63.3 ± 9.4‰，显著低于冬季（+7.2 ± 3.4‰和88.3 ± 12.1‰），这表明NOx来源与硝酸盐形成途径存在差异。δN-NO和δO-NO在夜间均有所升高，表明即使在夏季，NO水解也导致了夜间硝酸盐增加。夏季OH氧化途径对硝酸盐气溶胶的贡献平均为70.5 ± 17.0%，冬季硝酸盐生成以NO水解为主（约80%）。平均而言，夏季机动车尾气、煤炭燃烧、天然气燃烧和土壤排放对硝酸盐气溶胶的贡献分别为50.7%、21.5%、15.9%和11.9%，冬季对硝酸盐生成的贡献分别为56.8%、23.9%、13.6%和5.7%。值得注意的是，天然气燃烧是上海硝酸盐气溶胶不可忽视的来源。与δN-NO和PM呈负相关相反，冬季δO-NO值与硝酸盐浓度和气溶胶液态水含量（ALWC）呈正相关，这表明在平静和潮湿条件下，贫氮NOx的持续积累和快速的NO水解推动了硝酸盐的爆发式增长。为持续改善空气质量，应优先控制上海作为NOx和挥发性有机化合物（VOCs）主要来源的机动车排放。
