Ozone Formation Induced by Reactive Bromine and Iodine Species in a polluted marine environment

Reactive iodine and bromine species (RIS and RBS, respectively) are known for altering atmospheric chemistry, causing sharp tropospheric ozone (O₃) depletion in polar regions and significant O₃ reduction in the marine boundary layer (MBL). Here we use the comprehensive heterogeneous CAABA/MECCA atmospheric chemistry box model (CAABA/MECCA) to simulate the interaction between photochemistry and RBS and RIS, based on previous measurements at the Dead Sea (between N31°50^' and N31°00', E35°30') boundary layer. Unexpectedly, the model simulations showed that both RIS and RBS can lead to enhanced O₃ formation in a polluted marine environment under volatile organic compound (VOC)-limited conditions associated with high nitrogen oxide (NO_X = [NO] + [NO₂])concentrations¹. Under these conditions, the daily average O₃ mixing ratio increased up to 44% and 28% for BrO and IO mixing ratios of up to 6.8 ppt and 4.7 ppt, respectively. The increase in O₃ was partially induced by enhanced ClNO₃ formation for higher Br₂ and I₂ emission flux. The O₃ increase was associated with an increased mixing ratio of hydroperoxyl radical to hydroxyl radical ([HO₂]/[OH]) and increased [NO₂]/[NO] with higher RBS and/or RIS. NO_X-rich conditions are typical to the polluted MBL, near coastlines and ship plumes. Considering that O₃ is toxic to humans, plants and animals and is a greenhouse gas, and that the polluted MBL covers extensive inhabited areas of the earth's surface, our findings call for adequate updating of local and regional air-quality models with the effects of RBS and RIS activities on O₃ mixing ratios in the polluted MBL. References ¹ Shechner, M., and Tas, E., Ozone Formation Induced by the Impact of Reactive Bromine and Iodine Species on Photochemistry in a Polluted Marine Environment Environmental Science & Technology 2017 51 (24), 14030-14037, DOI: 10.1021/acs.est.7b02860.