Physical chemistry of airborne sea salt particles and their components

The potential for generation of highly reactive chlorine and bromine atoms from sea salt particles in the troposphere has been recognized for many yea rs. This chemistry is of particular interest because of the complex interac tions of halogen atoms with ozone as well as with organics, which can lead to either the formation or destruction of tropospheric ozone, depending on the conditions. While a variety of reactions of tropospherically important gases with sea salt and its major components, NaCl and NaBr, have been iden tified, the chemical and physical interactions are not well understood on a molecular scale. As a result, quantification of the contribution of sea sa lt chemistry to the marine boundary layer, as well as in other circumstance s where such chemistry may be important, is not yet possible. We discuss he re research from the authors' laboratories which is directed to understandi ng the chemistry of sea salt, NaCl, and NaBr on a molecular level in suffic ient detail to provide a firm basis for incorporating this heterogeneous ch emistry into atmospheric models. Implications for chemistry in the marine b oundary layer and in the Arctic at polar sunrise are discussed, and areas o f particular uncertainty highlighted.