Laboratory and modeling studies of the chemical mechanism for Cl2 production from the reaction of ozone with NaCl aerosol

Chlorine atoms are expected to be significant atmospheric oxidants. They are produced in marine areas where sea salt reactions with oxides of nitrogen and ozone release photochemically active chlorine species. In earlier studies in this laboratory, it was shown that Cl₂ is produced from the reaction of ozone with sea salt aerosol above its deliquescence point when irradiated at 254 nm at 1 atm and 298 K. Laboratory studies and modeling of the reaction of NaCl aerosol with ozone are being conducted in order to elucidate the chemical mechanism of Cl₂ production. A newly developed chemical box model incorporating all known gas phase and aqueous phase chemistry has been unable to explain the experimentally observed Cl₂ production. We report here the results of ongoing experimental studies in an aerosol chamber following Cl₂ production from the reaction of NaCl aerosol and ozone under variety of conditions including changing initial ozone concentration, aerosol size and concentration, relative humidity, and pH. In addition, we propose a surface process which explains the experimentally observed Cl₂ production and report the results of incorporation of this process into the model. The atmospheric significance of the experimentally observed Cl₂ production and the proposed surface process will be discussed.