Amines are semi-volatile derivatives of ammonia that can be present in atmosphere as result of agricultural practice, animal husbandry, fossil fuel combustion and other anthropogenic and natural sources1. Due to their acid-neutralizing capacity, amines can modify the acid/base nature of the interfaces of aerosols and cloud droplets, affecting the overall atmospheric chemistry balance at local and large scales2. The kinetic and thermodynamics of reactions strongly depend on the solvation environment in which such reactions occur. Concerning liquid aerosols, the mechanism could be different if the reactants are fully solvated in the bulk or at the interface. However, the solvation behavior of amines and their photochemical by-products on liquid aerosols is poorly understood and has not been systematically explored yet. We studied the adsorption and the solvation environment of methylamine, one of the most common amine present in the atmosphere, on the surface of liquid water aerosol. Using molecular dynamics simulations and quantum chemistry calculations, we investigated the energetics and dynamics of uptake and solvation of this compound at interfaces as well as the hydrogen bond network in the neighborhood of the adsorbed molecule. We evaluated the possible solvent/substrate effects that can affect the (photo)chemical activity obtaining physical insights that can be used to draw a comprehensive and general picture of amine behavior on aerosol surfaces. This information will help to clarify the compounds and/or (photo)chemical pathways that are more likely to occur, setting up the starting point for more accurate non-adiabatic dynamics and calculations for photo-excited reactions. At the same time, the simulations provide important information about the uptake and mass accommodation coefficients that are largely used in aerosol models for weather and air-quality predictions3. 1 Ge, X., Wexler, A.S. & Clegg, S.L. Atmospheric amines - Part I. A review. Atmospheric Environment 45, 524-546, doi:10.1016/j.atmosenv.2010.10.012 (2011). 2 Laskin, A., Laskin, J. & Nizkorodov, S.A. Chemistry of Atmospheric Brown Carbon. Chemical Reviews, 150226075918007, doi:10.1021/cr5006167 (2015). 3 Ervens, B. Modeling the Processing of Aerosol and Trace Gases in Clouds and Fogs. Chemical Reviews, 150421142119000, doi:10.1021/cr5005887 (2015).

Toward a comprehensive picture of amine uptake and solvation on the surface of liquid aerosols: A computational study

251st National Meeting (2016)

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