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 years. This chemistry is of particular interest because of the complex interactions 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 identified, the chemical and physical interactions are not well understood on a molecular scale. As a result, quantification of the contribution of sea salt chemistry to the marine boundary layer, as well as in other circumstances where such chemistry may be important, is not yet possible. We discuss here research from the authors' laboratories which is directed to understanding the chemistry of sea salt, NaCl, and NaBr on a molecular level in sufficient detail to provide a firm basis for incorporating this heterogeneous chemistry into atmospheric models. Implications for chemistry in the marine boundary layer and in the Arctic at polar sunrise are discussed, and areas of particular uncertainty highlighted.