Key Lab of Aerosol Chemistry and Physics, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, Shaanxi, 710061, China; University of the Chinese Academy of Sciences, Beijing, 100049, China.
School of Human Settlements and Civil Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi, 710049, China.
Environ Pollut. 2021 Jun 15;279:116931. doi: 10.1016/j.envpol.2021.116931. Epub 2021 Mar 11.
Stringent mitigation measures have reduced wintertime fine particulate matter (PM) concentrations by 42.2% from 2013 to 2018 in the Beijing-Tianjin-Hebei (BTH) region, but severe PM pollution still frequently engulfs the region. The observed nitrate aerosols have not exhibited a significant decreasing trend and constituted a major fraction (about 20%) of the total PM, although the surface-measured NO concentration has decreased by over 20%. The contributions of nitrogen oxides (NO) emissions mitigation to the nitrate and PM concentrations and how to alleviate nitrate aerosols efficiently under the current situation still remains elusive. The WRF-Chem model simulations of a persistent and heavy PM pollution episode in January 2019 in the BTH reveal that NO emissions mitigation does not help lower wintertime nitrate and PM concentrations under current conditions in the BTH. A 50% reduction in NO emissions only decreases nitrate mass by 10.3% but increases PM concentrations by 3.2%, because the substantial O increase induced by NO mitigation offsets the HNO loss and enhances sulfate and secondary organic aerosols formation. Our results are further consolidated by the occurrence of severe PM pollution in the BTH during the COVID-19 outbreak, with a significant reduction in NO concentration. Mitigation of NH emissions constitutes the priority measure to effectively lower the nitrate and PM concentrations in the BTH under current conditions, with 35.5% and 12.7% decrease, respectively, when NH emissions are reduced by 50%.
从 2013 年到 2018 年，京津冀地区采取了严格的减排措施，使得冬季细颗粒物（PM）浓度降低了 42.2%，但该地区仍频繁遭受严重的 PM 污染。尽管地面测量的 NO 浓度已经下降了 20%以上，但观测到的硝酸盐气溶胶并没有呈现出明显的下降趋势，仍然构成了 PM 的主要组成部分（约 20%）。氮氧化物（NO）减排对硝酸盐和 PM 浓度的贡献以及在当前情况下如何有效地缓解硝酸盐气溶胶仍然难以捉摸。WRF-Chem 模型对 2019 年 1 月京津冀地区一次持续且严重的 PM 污染事件的模拟表明，在当前京津冀地区的条件下，NO 减排并不能降低冬季硝酸盐和 PM 浓度。NO 排放减少 50%仅使硝酸盐质量减少 10.3%，但却使 PM 浓度增加 3.2%，因为 NO 减排引起的大量 O3 增加抵消了 HNO3 的损失，并促进了硫酸盐和二次有机气溶胶的形成。在 COVID-19 爆发期间，京津冀地区发生了严重的 PM 污染，NO 浓度显著下降，这进一步证实了我们的结果。在当前情况下，减排 NH3 是降低京津冀地区硝酸盐和 PM 浓度的优先措施，当 NH3 排放量减少 50%时，硝酸盐和 PM 浓度分别降低 35.5%和 12.7%。
