Aerosol Promotes Peroxyacetyl Nitrate Formation During Winter in the North China Plain
Aerosol Promotes Peroxyacetyl Nitrate Formation During Winter in the North China Plain
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华北平原冬季气溶胶促进过氧乙酰硝酸盐的形成
DOI：
10.1021/acs.est.0c08157
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发表时间：
2021
影响因子：
11.4
通讯作者：
Xiaobin Xu
中科院分区：
文献类型：
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作者：
Wanyun Xu;Gen Zhang;Ying Wang;Shengrui Tong;Wenqian Zhang;Zhiqiang Ma;Weili Lin;Ye Kuang;Liyuan Yin;Xiaobin Xu
过氧乙酰硝酸盐（PAN）是光化学污染的重要指标，在氮氧化物存在下，某些挥发性有机化合物（VOC）的光化学中形成类似于臭氧，并且在冬季显示出令人惊讶的高浓度，其与颗粒物而不是臭氧浓度更好地相关，原因仍然未知。在这项研究中，冬季观测PAN，VOCs，PM2.5，HONO，和各种微量气体进行了调查，找到气溶胶和冬季PAN形成之间的关系。冬季光化学污染是由高PAN浓度（平均值：1.2 ± 1.1 ppb，最大值：7.1 ppb），尽管臭氧浓度低。PAN浓度由其氧化VOC（OVOC）前体浓度和NO/NO2比值决定，并且可以基于对它们的化学关系的理解来很好地参数化。数据分析和箱模型的结果表明，PAN的形成主要是由VOC老化过程，涉及OH氧化或光解，而不是臭氧分解途径。气溶胶上的非均相反应提供了关键的光化学氧化剂，如HONO，其在光解时产生OH自由基，促进OVOC形成，从而增强PAN的产生，解释了观察到的PM2.5-OVOC-PAN相互关系。反过来，这些OVOCs的一部分可能参与形成二次有机气溶胶，进一步加重雾霾污染的反馈。冬季的低温使PAN能够远距离运输到顺风地区，这将如何影响它们的氧化能力和光化学污染，需要在未来的研究中进一步评估。
Peroxyacetyl nitrate (PAN) is an important indicator for photochemical pollution, formed similar to ozone in the photochemistry of certain volatile organic compounds (VOCs) in the presence of nitrogen oxides, and has displayed surprisingly high concentrations during wintertime that were better correlated to particulate rather than ozone concentrations, for which the reasons remained unknown. In this study, wintertime observations of PAN, VOCs, PM2.5, HONO, and various trace gases were investigated to find the relationship between aerosols and wintertime PAN formation. Wintertime photochemical pollution was affirmed by the high PAN concentrations (average: 1.2 ± 1.1 ppb, maximum: 7.1 ppb), despite low ozone concentrations. PAN concentrations were determined by its oxygenated VOC (OVOC) precursor concentrations and the NO/NO2ratios and can be well parameterized based on the understanding of their chemical relationship. Data analysis and box modeling results suggest that PAN formation was mostly contributed by VOC aging processes involving OH oxidation or photolysis rather than ozonolysis pathways. Heterogeneous reactions on aerosols have supplied key photochemical oxidants such as HONO, which produced OH radicals upon photolysis, promoting OVOC formation and thereby enhancing PAN production, explaining the observed PM2.5–OVOC–PAN intercorrelation. In turn, parts of these OVOCs might participate in the formation of secondary organic aerosol, further aggravating haze pollution as a feedback. Low wintertime temperatures enable the long-range transport of PAN to downwind regions, and how that will impact their oxidation capacity and photochemical pollution requires further assessment in future studies.