Impact of Chlorine Emissions from Sea-Salt Aerosol on Coastal Urban Ozone

The ability of photochemical models to predict observed coastal chlorine levels and their corresponding effect on ozone formation is explored. Current sea-spray generation functions, a comprehensive gas-phase chlorine chemistry mechanism, and several heterogeneous/multiphase chemical reactions considered key processes leading to reactive chlorine formation are added to an airshed model of the South Coast Air Basin of California. Modeling results reproduce regional sea-salt particle concentrations. The heterogeneous/multiphase chemical reactions do not affect the rate of hydrochloric acid displacement, nor do they enhance aerosol nitrate formation. Chlorine levels in the model are predicted to be an order of magnitude lower than previously observed values at other coastal regions under similar conditions, albeit in much better agreement than previous studies. The results suggest that the inclusion of sea-salt-derived chlorine chemistry might increase morning ozone predictions by as much as 12 ppb in coastal regions and by 4 ppb in the peak domain ozone in the afternoon. The inclusion of anthropogenic sources of chlorine is recommended for future studies, as such sources might elevate ozone predictions even further via direct emission into polluted regions.