Adsorption and heterogeneous reactions of ClONO2 and N2O5 on/with NaCl aerosol

Abstract

The adsorption and heterogeneous reactions of ClONO₂ and N₂O₅ on the NaCl (100) surface have been investigated by performing density functional theory (DFT) calculations. Possible adsorption structures, energies and electronic properties of ClONO₂ and N₂O₅ were studied by considering multiple possible adsorption sites without symmetry restriction. The most stable adsorption configurations are a vertical adsorption mode for ClONO₂ and a horizontal adsorption mode for N₂O₅, with the adsorption energies of 14.81 and 13.67 kcal mol⁻¹, respectively. Two possible reactions were proposed on the NaCl (100) surface. Adsorbed ClONO₂ and N₂O₅ could react with HCl or hydrolyze on the NaCl surface to form HNO₃ and other gaseous species (Cl₂, HOCl and ClNO₂). More importantly, ClONO₂ and N₂O₅ can actively participate in the heterogeneous reaction with NaCl to generate Cl₂ and ClNO₂, which could be photolyzed to produce reactive chlorine atoms. The adsorbed H₂O molecule plays an important role in the key elementary step and promotes the formation of the products. The present results rationalize previous experimental studies well and enrich our understanding of the source of halogen atoms in the marine boundary layer.