Impact of the quasi-liquid layer on the surface of ice on relevant atmospheric chemical processes: Adsorption and photochemistry of PAHs at the air-ice interfaces

A disordered quasi-liquid layer (QLL) exists on ice surfaces and its thickness increases with temperature and ionic solute concentration. The ice-QLL is a specific environment where many important atmospheric chemical processes occur. In particular, PAHs are known to undergo heterogeneous photochemical reactions in the polar boundary layer and in the snowpack. Different studies suggest that the photochemistry on ice can be distinctly different from bulk water or the air-water interface. The unique solute-solute and solute-solvent interactions in the QLL can be detected in the photoemission/absorption spectra. Using a combined molecular dynamics/ab-initio computational approach, we study adsorption of several PAHs (naphthalene, methylnaphthalene and dibenzyl keton) onto ice surface and their structural organization and dynamics in the ice-QLL. In addition, we investigate the effect of the QLL environment on the absorption and emission spectra of these PAH species. These results will help to improve our understanding of the tropospheric chemical processes.