Heterogeneous chemistry in the troposphere: experimental approaches and applications to the chemistry of sea salt particles

Halogen atoms, particularly chlorine atoms, are well known to be highly rea ctive and to play a central role in the chemistry of the upper atmosphere. A large potential source of these halogens in the lower atmosphere (troposp here) exists in the form of sea salt particles. A variety of laboratory, fi eld and modelling studies strongly suggests that there are heterogeneous re actions of sea salt particles which generate photochemically active halogen species such as CI, in marine areas. In addition, there is increasing evid ence for a contribution of bromine atoms to tropospheric chemistry in marin e regions at high latitudes. We review here briefly the potential importanc e of such halogen reactions and evidence for their role in the chemistry of the troposphere. Studies carried out in this laboratory to elucidate, at a molecular level, the mechanisms of reaction of synthetic sea salt and its components with gases of tropospheric interest are reviewed. Initial result s obtained using a new aerosol apparatus recently constructed in this labor atory to study the reactions of aerosol particles above and below the deliq uescence point of the salts are also discussed.