McNamara Stephen M, Kolesar Katheryn R, Wang Siyuan, Kirpes Rachel M, May Nathaniel W, Gunsch Matthew J, Cook Ryan D, Fuentes Jose D, Hornbrook Rebecca S, Apel Eric C, China Swarup, Laskin Alexander, Pratt Kerri A
Department of Chemistry, University of Michigan, Ann Arbor, Michigan, United States.
Department of Meteorology and Atmospheric Science, The Pennsylvania State University, University Park, Pennsylvania, United States.
ACS Cent Sci. 2020 May 27;6(5):684-694. doi: 10.1021/acscentsci.9b00994. Epub 2020 May 13.
Inland sources of particulate chloride for atmospheric nitryl chloride (ClNO) formation remain unknown and unquantified, hindering air quality assessments. Globally each winter, tens of millions of tons of road salt are spread on roadways for deicing. Here, we identify road salt aerosol as the primary chloride aerosol source, accounting for 80-100% of ClNO formation, at an inland urban area in the wintertime. This study provides experimental evidence of the connection between road salt and air quality through the production of this important reservoir for nitrogen oxides and chlorine radicals, which significantly impact atmospheric composition and pollutant fates. A numerical model was employed to quantify the contributions of chloride sources to ClNO production. The traditional method for simulating ClNO considers chloride to be homogeneously distributed across the atmospheric particle population; yet, we show that only a fraction of the particulate surface area contains chloride. Our new single-particle parametrization considers this heterogeneity, dramatically lowering overestimations of ClNO levels that have been routinely reported using the prevailing methods. The identification of road salt as a ClNO source links this common deicing practice to atmospheric composition and air quality in the urban wintertime environment.
大气中用于形成硝酰氯（ClNO）的颗粒态氯化物的内陆来源仍不明确且未得到量化，这阻碍了空气质量评估。在全球范围内，每年冬天都有数百万吨道路融雪盐被撒在道路上用于除冰。在此，我们确定道路融雪盐气溶胶是主要的氯化物气溶胶来源，在冬季的一个内陆城市地区，它占ClNO形成量的80% - 100%。这项研究提供了实验证据，证明道路融雪盐与空气质量之间存在联系，即通过产生这种对氮氧化物和氯自由基的重要储存库，这对大气成分和污染物归宿有显著影响。我们采用了一个数值模型来量化氯化物来源对ClNO生成的贡献。传统模拟ClNO的方法认为氯化物在大气颗粒物群体中是均匀分布的；然而，我们表明只有一部分颗粒表面积含有氯化物。我们新的单颗粒参数化方法考虑了这种非均质性，极大地降低了使用现有方法常规报告的ClNO水平的高估情况。将道路融雪盐确定为ClNO来源，将这种常见的除冰做法与城市冬季环境中的大气成分和空气质量联系了起来。
