During atmospheric transport aerosol particles undergo physicochemical transformations as a result of gas-surface interactions and multiphase chemical reactions. Prediction of the particle evolution remains challenging due to the large compositional variety of airborne particulate matter and gas species, in addition to the wide temperature and humidity range present in the atmosphere, and the complex underlying molecular processes governing the uptake of gases and chemical reaction pathways. Adsorption of gas species at the surface of a liquid or solid material, either as physisorption or chemisorption, represents the first step of uptake and multiphase chemical reactions. The desorption life time is a crucial parameter in the description of the interaction between gas species and substrates. Desorption is convoluted with elementary reactive and non-reactive processes including reactive and non-reactive uptake, surface and bulk reaction, and gas-particle partitioning. The residence time of adsorbed gas species will depend strongly on temperature, where lower tropospheric temperatures yield significantly increased desorption lifetimes. This effect can potentially counteract slow rates of chemical reaction and diffusion and enhance the overall gas uptake which can involve reversible, reactive, and catalytic processes operating in parallel or sequentially on the surface or in the bulk of the particles. Applying gas-substrate kinetic flux simulations, we demonstrate the impact of desorption life on reactive and non-reactive uptake for solid and liquid substrates for typical tropospheric temperatures. Compilation of a large thermodynamic data set of gas-substrate systems allows us to develop a parameterization of the desorption energy, valid for a wide range of inorganic and organic gas species and substrate types. The input parameters are typical observables such as molar mass, molecular structure, and oxidation state. We show that this parameterization can be applied for an improved understanding of secondary organic aerosol partitioning via the concept of molecular corridors using saturation mass concentration. Furthermore, we find a strong relationship between the parameterized desorption energy and the glass transition temperature of the condensed phase organic species.

Impact of adsorption energies on gas-surface interactions and multiphase chemical kinetics

2019 Fall National Meeting

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