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Ozone Formation Induced by the Impact of Reactive Bromine and Iodine Species on Photochemistry in a Polluted Marine Environment

Shechner, M., Tas, E.
Environmental science & technology 2017 v.51 no.24 pp. 14030-14037
air quality, atmospheric chemistry, bromine, coasts, greenhouse gases, humans, hydroxyl radicals, iodine, marine environment, mixing, models, nitric oxide, nitrogen dioxide, ozone, photochemistry, plants (botany), toxicity, troposphere, volatile organic compounds, water pollution, Polar Regions
Reactive iodine and bromine species (RIS and RBS, respectively) are known for altering atmospheric chemistry and causing sharp tropospheric ozone (O₃) depletion in polar regions and significant O₃ reduction in the marine boundary layer (MBL). Here we use measurement-based modeling to show that, unexpectedly, 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 (NOX = [NO] + [NO₂]) concentrations. Under these conditions, the daily average O₃ mixing ratio increased to ∼44 and ∼28% for BrO and IO mixing ratios of up to ∼6.8 and 4.7 ppt, respectively. The increase in the level of O₃ was partially induced by enhanced ClNO₃ formation for higher Br₂ and I₂ emission flux. The increase in the level of O₃ was associated with an increased mixing ratio of hydroperoxyl radical to hydroxyl radical ([HO₂]/[OH]) and increased [NO₂]/[NO] with higher levels of RBS and/or RIS. NOX-rich conditions are typical of the polluted MBL, near coastlines and ship plumes. Considering that O₃ is toxic to humans, plants, and animals and is a greenhouse gas, our findings call for adequate updating of local and regional air-quality models with the effects of activities of RBS and RIS on O₃ mixing ratios in the polluted MBL.