Ozone formation induced by the impact of reactive bromine and iodine species on photochemistry in a polluted marine environment

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 t...