Urban grime can be an important substrate for heterogeneous reactions in cities. Studies performed using laboratory-prepared urban grime proxies and urban grime collected from the field indicate that the physicochemical properties of urban grime can greatly affect heterogeneous reaction rate constants. We investigated several properties of urban grime collected from two cities in the north-east region of the United States of America. Optical and Raman microscopy indicated that urban grime collected from these regions consists primarily of particles as opposed to a uniform film. Total carbon analysis and ion chromatography were used to determine the bulk composition of the urban grime from both cities. Comparing these results to reported compositions of urban grime from cities in Canada and Europe showed strong similarities between different locations, with some variations for specific ions, such as higher chloride levels in North American cities and higher sulfate levels in some European cities. Absorbance spectra demonstrated that urban grime can absorb sunlight across the ultraviolet region. It may therefore be able to participate in photochemical reactions (either hindering them via processes such as the inner filter effect or enhancing them via processes such as photosensitization).

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从两个城市取样的城市污垢的理化特性

城市污垢可能是城市异质反应的重要底物。使用实验室制备的城市污垢代理和从现场收集的城市污垢进行的研究表明，城市污垢的理化特性会极大地影响异质反应速率常数。我们调查了从美国东北地区的两个城市收集的城市污垢的几种特性。光学和拉曼显微镜表明，从这些区域收集的城市污垢主要由颗粒组成，而不是均匀的薄膜。使用总碳分析和离子色谱法确定两个城市的城市污垢的总体组成。将这些结果与加拿大和欧洲城市中报告的城市污垢成分进行比较后，发现不同地点之间的相似性很强，某些特定离子存在一些差异，例如北美城市中的氯化物含量较高，欧洲一些城市中的硫酸盐含量较高。吸收光谱表明，城市污垢可以吸收整个紫外线区域的阳光。因此，它可能能够参与光化学反应（通过诸如内部过滤作用的过程阻止它们，或者通过诸如光敏化的过程来增强它们）。