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Technical note: Examining ozone deposition over seawater
Citation:
Sarwar, G., D. Kang, K. Foley, D. Schwede, B. Gantt, AND R. Mathur. Technical note: Examining ozone deposition over seawater. ATMOSPHERIC ENVIRONMENT. Elsevier Science Ltd, New York, NY, 141:255–262, (2016).
Impact/Purpose:
The National Exposure Research Laboratory (NERL) Computational Exposure Division (CED) develops and evaluates data, decision-support tools, and models to be applied to media-specific or receptor-specific problem areas. CED uses modeling-based approaches to characterize exposures, evaluate fate and transport, and support environmental diagnostics/forensics with input from multiple data sources. It also develops media- and receptor-specific models, process models, and decision support tools for use both within and outside of EPA.
Description:
Surface layer resistance plays an important role in determining ozone deposition velocity over sea-water and can be influenced by chemical interactions at the air-water interface. Here, we examine the effect of chemical interactions of iodide, dimethylsulfide, dissolved organic carbon, and bromide in seawater on ozone deposition. We perform a series of simulations using the hemispheric Community Multiscale Air Quality model for summer months in the Northern Hemisphere. Our results suggest that each chemical interaction enhances the ozone deposition velocity and decreases the atmospheric ozone mixing ratio over seawater. Iodide enhances the median deposition velocity over seawater by 0.023 cm s−1, dissolved organic carbon by 0.021 cm s−1, dimethylsulfide by 0.002 cm s−1, and bromide by ∼0.0006 cm s−1. Consequently, iodide decreases the median atmospheric ozone mixing ratio over seawater by 0.7 ppb, dissolved organic carbon by 0.8 ppb, dimethylsulfide by 0.1 ppb, and bromide by 0.02 ppb. In a separate model simulation, we account for the effect of dissolved salts in seawater on the Henry’s law constant for ozone and find that it reduces the median deposition velocity by 0.007 cm s−1 and increases surface ozone mixing ratio by 0.2 ppb. The combined effect of these processes increases the median ozone deposition velocity over seawater by 0.040 cm s−1, lowers the atmospheric ozone mixing ratio by 5%, and slightly improves model performance relative to observations.
