Global Bromine- and Iodine-Mediated Tropospheric Ozone Loss Estimated Using the CHASER Chemical Transport Model

We quantified the global bromine- and iodine-mediated tropospheric ozone loss using global chemical transport model simulations. We tested three datasets of very short-lived substances (VSLS) emissions, three datasets of sea surface iodide concentrations, and an explicit representation of the effects of multi-phase reactions at the air-sea boundary on dry deposition. We then determined optimal model settings based on the evaluation using the ship-borne and aircraft-campaign observations over the ocean. Our evaluation suggested that the explicit representation of multi-phase reaction effects substantially reduced model biases of ozone in the lower troposphere (up to 11%). Moreover, the impacts of using different datasets of VSLS emissions and sea-surface iodide concentrations were relatively small. The global bromine- and iodine-mediated chemical ozone losses were estimated to account for 4% and 17% of the total chemical loss, respectively, while the global iodine-mediated dry deposition loss of ozone was estimated to account for 22% of the global total dry deposition. These bromine- and iodine-mediated ozone losses decreased surface ozone concentrations over the ocean by 10% and 23%, respectively. The observational constraint on model simulations made by this study supports that bromine and iodine substantially impact global tropospheric ozone through atmospheric chemical reactions and dry deposition processes.