(730h) Atmospheric Oxidation of Benzene: Effect of Temperature and Ionic Strength in Both the Bulk Aqueous Phase and At the Air-Water Interface

Atmospheric water droplets, such as fog and clouds, can differ broadly in both ionic strength and pH. In the atmosphere, benzene, a common aromatic pollutant resulting from both stationary (chemical and petrochemical industry emissions) and mobile sources (automobile exhaust), reacts with hydroxyl radicals to form two main products, phenol and biphenyl. Although aromatic compounds are generally very stable, benzene is known to react easily with hydroxyl radicals in both the gas phase (k_OH = 4.3×10⁴ µM^-1·min^-1)¹ and the aqueous phase (k_OH = 4.7×10⁵ µM^-1·min^-1)².

In the bulk aqueous phase, higher temperatures and an increase of ionic strength have been shown to enhance the degradation of both benzene and phenol as well as the formation of biphenyl. However, reactions in atmospheric droplets are not solely governed by the bulk phase; instead, it is the reactions at the air-water interface that predominately dominate the reactivity of the droplet. The surface is also known to have an affinity for both aromatic compounds and hydroxyl radicals^3-6, which could influence compound fate given the large specific surface area of fog and clouds⁷. Moreover, the surface can have a different ionic strength than the bulk aqueous phase, which in turn can affect the overall reaction rate. Thus, in this study, a thin film reactor is used to evaluate how both temperature and ionic strength affects the degradation of benzene at the air-water interface. In particular, this study focuses on the photo-generation of hydroxyl radicals by UVB irradiation of hydrogen peroxide, which has relevance for aqueous atmospheric systems. These results from the interface are compared to the previous results found within the bulk aqueous phase.

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