Department of Earth System Science, Tsinghua University, Beijing, 100084, China.
School of Environment, Tsinghua University, Beijing, 100084, China.
Environ Pollut. 2021 Oct 15;287:117625. doi: 10.1016/j.envpol.2021.117625. Epub 2021 Jun 23.
In recent years, severe air pollution still frequently occurs in winter despite the effective implementation of clean air actions in China. Therefore, field measurements of particle composition and gas precursors were collected from December 1, 2018 to January 15, 2019 at an urban site in a central Chinese city to investigate the existing mechanisms of pollution. The hourly averaged PM concentration during the campaign was 92.7 μg m, with nitrate and organic aerosol (OA) demonstrated as the principal components. Generally, NO oxidation in the daytime was observed as the major mechanism for nitrate generation, and aerosol water content (AWC) showed its influential role with the associated increases in the nitrogen oxidation and nitrate partitioning ratios. When AWC increased from dozens to hundreds of μg m after the afternoon, nocturnal NO hydrolysis was demonstrated as the overriding mechanism and provoked extreme contamination of nitrates. Five sources of organic aerosols (OAs) were identified: hydrocarbon-like OAs (HOAs, 16.5%), coal combustion OAs (CCOAs, 19.2%), biomass burning OAs (BBOAs, 9.9%), semi-volatile oxygenated OAs (SV-OOAs, 29.4%), and low-volatile oxygenated OAs (LV-OOAs, 25.0%). SV-OOAs and LV-OOAs were identified as gasSOAs and aqSOAs according to their sensitivities to the atmospheric oxidation capacity and AWC. In addition, aqueous-phase processing was found to be the dominant pathway for SOA formation when the AWC concentration was higher than 80 μg m. As an influential factor for nitrate and SOA formation, AWC could be greatly affected by RH and the concentrations of inorganic species. Sulfate, which was mainly contributed by anthropogenic emissions, was demonstrated to be a significant factor for active aqueous phase reactions, although SO has been dramatically reduced in recent years. Above all, this study revealed the significant role of AWC in current pollution episode in winter, and will assist in establishing future measures for pollution mitigation.
近年来，尽管中国有效实施了清洁空气行动，但冬季仍频繁出现严重的空气污染。因此，在中国中部的一个城市的城区采集了 2018 年 12 月 1 日至 2019 年 1 月 15 日的颗粒物组成和气体前体的现场测量数据，以调查污染的现有机制。在该研究期间，每小时平均 PM 浓度为 92.7μg/m ，硝酸盐和有机气溶胶（OA）是主要成分。通常，观察到白天的 NO 氧化是硝酸盐生成的主要机制，气溶胶水含量（AWC）显示出其影响作用，氮氧化物的增加和硝酸盐的分配比例也随之增加。当 AWC 在下午从数十微克增加到数百微克后，夜间的 NO 水解被证明是主要机制，并导致硝酸盐的极度污染。鉴定出五种有机气溶胶（OA）的来源：烃类 OA（HOAs，16.5％），煤燃烧 OA（CCOAs，19.2％），生物质燃烧 OA（BBOAs，9.9％），半挥发性含氧 OA（SV-OOAs，29.4％）和低挥发性含氧 OA（LV-OOAs，25.0％）。根据其对大气氧化能力和 AWC 的敏感性，SV-OOAs 和 LV-OOAs 被鉴定为气体 SOAs 和 aqSOAs。此外，当 AWC 浓度高于 80μg/m 时，发现水相处理是 SOA 形成的主要途径。作为硝酸盐和 SOA 形成的影响因素，AWC 可能会受到 RH 和无机物质浓度的极大影响。硫酸盐主要由人为排放贡献，尽管近年来 SO 已大大减少，但它被证明是活跃水相反应的重要因素。总之，本研究揭示了 AWC 在冬季当前污染事件中的重要作用，并将有助于制定未来的污染缓解措施。
