The persistence of a proxy for cooking emissions in megacities: a kinetic study of the ozonolysis of self-assembled films by simultaneous small and wide angle X-ray scattering (SAXS/WAXS) and Raman microscopy,Faraday Discussions

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The persistence of a proxy for cooking emissions in megacities: a kinetic study of the ozonolysis of self-assembled films by simultaneous small and wide angle X-ray scattering (SAXS/WAXS) and Raman microscopy
Faraday Discussions ( IF 3.3 ) Pub Date : 2020-9-7 , DOI: 10.1039/d0fd00088d
Adam Milsom ₁ , Adam M Squires , Ben Woden , Nicholas J Terrill , Andrew D Ward , Christian Pfrang

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Cooking emissions account for a significant proportion of the organic aerosols emitted into the urban environment and high pollution events have been linked to an increased organic content on urban particulate matter surfaces. We present a kinetic study on surface coatings of self-assembled (semi-solid) oleic acid–sodium oleate cooking aerosol proxies undergoing ozonolysis. We found clear film thickness-dependent kinetic behaviour and measured the effect of the organic phase on the kinetics for this system. In addition to the thickness-dependent kinetics, we show that significant fractions of unreacted proxy remain after extensive ozone exposure and that this effect scales approximately linearly with film thickness, suggesting that a late-stage inert reaction product may form and inhibit reaction progress – effectively building up an inert crust. We determine this by using a range of simultaneous analytical techniques; most notably Small-Angle X-ray Scattering (SAXS) has been used for the first time to measure the reaction kinetics of films of a wide range of thicknesses from ca. 0.59 to 73 μm with films <10 μm thick being of potential atmospheric relevance. These observations have implications for the evolution of particulate matter in the urban environment, potentially extending the atmospheric lifetimes of harmful aerosol components and affecting the local urban air quality and climate.

中文翻译：

大城市烹饪排放代理的持续存在：通过同时小角和广角 X 射线散射 (SAXS/WAXS) 和拉曼显微镜对自组装薄膜的臭氧分解的动力学研究

烹饪排放占排放到城市环境中的有机气溶胶的很大一部分，高污染事件与城市颗粒物表面有机含量的增加有关。我们对进行臭氧分解的自组装（半固体）油酸-油酸钠蒸煮气溶胶代理的表面涂层进行了动力学研究。我们发现了清晰的薄膜厚度依赖性动力学行为，并测量了有机相对该系统动力学的影响。除了依赖于厚度的动力学外，我们还表明，在大量臭氧暴露后，仍有相当一部分未反应的代理物存在，并且这种效应与薄膜厚度大致呈线性关系，这表明后期惰性反应产物可能会形成并抑制反应进程——有效形成惰性外壳。我们通过使用一系列同步分析技术来确定这一点；最值得注意的是，小角 X 射线散射 (SAXS) 首次用于测量各种厚度的薄膜的反应动力学，从约 0.59 至 73 μm，薄膜厚度小于 10 μm，具有潜在的大气相关性。这些观测结果对城市环境中颗粒物的演变具有重要意义，可能会延长有害气溶胶成分的大气寿命，并影响当地城市空气质量和气候。

更新日期：2020-09-07

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