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Chemical effect on ozone deposition over seawater
Sarwar, G., B. Gantt, D. Kang, D. Schwede, R. Mathur, AND R. Schlitzer. Chemical effect on ozone deposition over seawater. CMAS, Chapel Hill, NC, October 05 - 07, 2015.
The National Exposure Research Laboratory’s Atmospheric Modeling Division (AMAD) conducts research in support of EPA’s mission to protect human health and the environment. AMAD’s research program is engaged in developing and evaluating predictive atmospheric models on all spatial and temporal scales for forecasting the Nation’s air quality and for assessing changes in air quality and air pollutant exposures, as affected by changes in ecosystem management and regulatory decisions. AMAD is responsible for providing a sound scientific and technical basis for regulatory policies based on air quality models to improve ambient air quality. The models developed by AMAD are being used by EPA, NOAA, and the air pollution community in understanding and forecasting not only the magnitude of the air pollution problem, but also in developing emission control policies and regulations for air quality improvements.
Surface layer resistance plays an important role in determining ozone deposition velocity over seawater. Recent studies suggest that surface layer resistance over sea-water is influenced by wind-speed and chemical interaction at the air-water interface. Here, we investigate the effect of chemical interaction of iodide, dimethyl sulfide (DMS) and dissolved organic carbon (DOC) in seawater with atmospheric ozone on ozone deposition by using a resistance scheme that accounts for the effects of wind-speed and chemical interaction. Four different model simulations are performed using the hemispheric Community Multiscale Air Quality model for summer months in 2006. The first simulation is completed by including the surface layer resistance due only to wind-speed. The second, third, and forth simulations are completed by including the surface layer resistance due to wind-speed and the chemical effects of iodide, DMS, and DOC in seawater. Oceanic iodide levels are estimated using the sea surface temperature, DMS levels are obtained from the oceanic climatological DMS database, and DOC levels are obtained from an ocean model based on coupled physical/biogeochemical processes. Preliminary results suggest that each chemical interaction enhances ozone deposition velocity and decreases ozone over marine environments. Compared to the median ozone deposition velocity of 0.007 cm/sec from the wind-speed-based surface layer resistance, the iodide/ozone reaction enhances the median deposition velocity over marine regions by 0.02 cm/sec, the DMS/ozone reaction by 0.002 cm/sec, and the DOC/ozone reaction by 0.02 cm/sec. Consequently the iodide/ozone reaction decreases the median ozone by 0.61 ppbv, the DMS/ozone reaction by 0.06 ppbv, and the DOC/ozone reaction by 0.68 ppbv. Thus, the effects of the iodide/ozone and DOC/ozone reactions on ozone deposition are similar while the effect of the DMS/ozone reaction is much smaller. However, the magnitudes of these impacts have substantial spatial variation. The paper contains a discussion of the spatial impacts on ozone deposition velocity and atmospheric ozone and a comparison with observed data.