Much of what we know about aqueous aerosol chemistry – reaction rates, products, mechanisms, and photolytic pathways – comes from extrapolating bulk aqueous phase lab simulations to atmospheric conditions.  Is this extrapolated knowledge reliable?  In the case of surface-enhanced reactions, the answer is “probably not.”  This class of reactions includes, of course, those involving reactants or products that are surface active – compounds that preferentially move to an aerosol particle surface.  For example, methylglyoxal, and the products of its reactions with ammonia and ammonium salts, have been shown to be surface active.  Interestingly, even some non-surface-active compounds such as glyoxal show greatly enhanced reaction rates in aqueous aerosol experiments compared to bulk liquid experiments.  This “aerosol enhancement” appears to be due not only to concentration increases caused by the evaporation of water but also hydration / dehydration reactions taking place at the gas-liquid interface.   Many other chemical processes occurring in aqueous aerosol particles, including acetal and aldol oligomer formation pathways, also involve hydration and dehydration reactions.   There is evidence that these oligomerization pathways, too, have higher reaction rates in aerosol particles than in bulk liquids.  This highlights the need to validate bulk aqueous experimental results with those from aqueous aerosol experiments performed in chambers, in order to identify reactions and systems that are surface-enhanced.

Enhanced reactivity in aqueous aerosols:  Why bulk-phase aqueous measurements can mislead us

253rd National Meeting (2017)

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