Modeling the Effect of Iodide Distribution on Ozone Deposition to Seawater Surface (Formerly J6.4)

Spatial changes in the dry deposition of ozone to the sea associated with ozone uptake by the dissolved iodide ions were analyzed in the northwestern Gulf of Mexico using the Community Multiscale Air Quality Model (CMAQ). The dry deposition module in CMAQ was modified using a formula developed by Chang et al. (2004) which accounts for chemical enhancement by iodide reacting with ozone in seawater. In addition, an attempt was made to incorporate iodide concentrations from the satellite-derived estimates of near-surface chlorophyll a concentrations into the CMAQ gridded fields. One-month CMAQ simulations conducted with the modified module including iodide reaction showed a significant increase in the dry deposition velocity of ozone to the sea, especially Texas and Louisiana Coast corresponding to the area with high iodide concentrations. On average, about 70 % enhancement of ozone dry deposition velocity over the sea water is attributed to the iodide effect alone. Interestingly, a small decrease in deposition amounts was found just inland from the shoreline, indicating that the iodide interaction can also affect ozone concentration in the inland coastal area. An in-depth analysis of 6-7 August showed that the enhancement of dry deposition velocity by the iodide reaction can make a noticeable contribution to both deposition amounts and ambient concentrations in the coastal area associated land-sea circulation: maximum decrease of about 2.5 ppb was founded over the offshore area from Galveston Island.