A variety of laboratory, field, and modeling studies strongly suggests that heterogeneous reactions of sea salt particles can generate photochemically active halogen species such as chlorine radicals in marine areas. There is also evidence that chlorine radicals can take part in the tropospheric gas-phase chemical reactions that lead to the formation or destruction of ozone. Although gas-phase reaction mechanisms involving chlorine radicals are available, a chlorine emissions inventory does not exist.
This research project developed a spatially and temporally distributed chlorine gas emissions inventory for the South Coast Air Basin. The chlorine emissions inventory was generated by combining the most recent knowledge of gas-phase and aqueous-phase (aerosol phase) chemistry with a state-of-the-science wind-driven sea-salt emissions model. A photochemical modeling study was performed to determine whether urban photochemical models simulating sea-salt particle chemistry can predict observed chlorine levels and how such chlorine levels affect the ozone formation. A host urban airshed model, employing a rich chemical mechanism and simulating aerosol dynamics, was augmented with 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. Modeling results adequately reproduce regional sea-salt particle concentrations. The results suggest that inclusion of sea-salt derived chlorine chemistry could increase morning ozone predictions by as much as ~12 ppb in coastal regions and by ~4 ppb to the peak domain ozone in the afternoon. Peak ozone concentrations at most monitoring sites increase by 2 - 4 ppb and even higher ozone increases, up to 7 ppb, are predicted at other times not coinciding with the peak. An emissions inventory of anthropogenic sources of chlorine is recommended as these may enhance ozone formation even further by emitting chlorine gases directly into polluted regions.
Donald Dabdub is an Associate Professor of Mechanical and Environmental Engineering at the University of California, Irvine. He completed his Ph.D. in Chemical Engineering at the California Institute of Technology in 1995. Professor Dabdub's expertise is in mathematical modeling of air pollution dynamics and numerical algorithms using high performance parallel computation. He has worked on several projects funded by the Environmental Protection Agency, National Science Foundation--Division of Advanced Scientific Computing, California Air Resources Board, Department of Energy, California Energy Commission, IBM Corporation, and EPRI developing new physics and chemistry for air quality models, designing new algorithms for the numerical solution of the overrunning equations of air pollution dynamics, and implementing urban photochemical models on concurrent computers.
Recently he has been developing a parallel implementation of dynamics of secondary organic aerosols and chemistry of chlorine in the troposphere. Professor Dabdub is the recipient of a career award from National Science Foundation. He presented the Schiesser distinguished lecture at Lehigh University. Furthermore, he was awarded the Prometheus Teaching award for excellence.
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