Ice growth from supercooled aqueous solutions of reactive oxygen species

Abstract

Classical molecular dynamics simulations and potential of mean force calculations were performed to study (1) the adsorption of several reactive oxygen species (ROSs, namely · OH, · HO2 and H2O2) on atmospheric air/ice interfaces and (2) the growth of ice from supercooled aqueous solutions of these ROSs. Free energy minima were observed for these ROSs at the air/ice interfaces. The presence of ROSs in supercooled water during the freezing process leads to the formation of quasi-liquid layers (QLLs) that were thicker than those formed from freezing of pure supercooled water. The ROSs in the supercooled water were always displaced to the air/ice interface during the freezing process at 270 K, but if the freezing process is carried out at 260 K, a significant fraction of hydroperoxy and hydrogen peroxide become trapped by the growing ice lattice. We also studied freezing of supercooled aqueous solutions containing ROSs and benzene, with 1-octanal at the interfaces with air. The structure of ice is not significantly altered by hydroperoxy, hydrogen peroxide, or benzene being trapped in the ice lattice. The presence of 1-octanal at the interfaces does not alter the trends described above; however, thinner QLLs are formed after the freezing process, and 1-octanal tends to slow down the dynamics of ROSs and aromatics at the air/ice interface.