Interfacial chemistry involving aldehyde (e.g., glyoxal and methylglyoxal, GLY and MGLY respectively) at aerosol surfaces is believed to catalyze aerosol growth, affecting light scattering and, thus, the overall atmospheric radiative budget and dynamics. The suggested pathway for aerosol growth relies on the hydrolysis of adsorbed GLY and MGLY. The mechanism of this hydrolysis remains disputed: despite the substantial reaction barriers it occurs even at low relative humidity and in absence of atmospheric acid.  Results from state-of-the-art classical and <i>first-principle</i>molecular dynamics simulations combined with advanced free energy methods on the solvation and hydrolysis of GLY and MGLY in bulk and on the surface of liquid water shall be presented. When compared to the gas phase, the trans to cis isomerization of GLY and MGLY at the liquid water interface is preferentially catalyzed. Additionally, cis conformation is selectively solvated within the bulk to a greater degree than is the trans. These two processes, i.e., the catalytic effect at the water interface and the differentially selective solvation, work together to modulate the relative concentration of different conformers at the water interface.  The isomerization determines the chemical pathways for the hydrolysis of GLY and MGLY on the water surface: free energy profiles show, indeed, that the reaction evolves with a simultaneous rotation of the molecular plane. While the reaction still remains more favorable in acid environment, the molecule isomerization lowers the free energy barrier for the reaction, which could explain why the reaction could be observed even in absence of atmospheric acid.  The isomerization of GLY and MGLY at the liquid water interface has important consequences for the interpretation of related experiments and for the modeling of glyoxal chemistry both at the interface of liquid droplets and aerosols. Broader implications of this work relate to describing the role of interfaces in selecting specific conformational structures at interfacial environments and in conformationally controlled chemistry.

Toward a comprehensive picture of heterogeneous chemistry at atmospheric aerosols: Solvation and hydrolysis of glyoxal and methylglyoxal at the liquid water aerosols interface

2019 Fall National Meeting

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