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

Typhoon- and pollution-driven enhancement of reactive bromine in the mid-latitude marine boundary layer

Tropospheric reactive bromine is important for atmospheric chemistry, regional air pollution, and global climate. Previous studies have reported measurements of atmospheric reactive bromine species in different environments, and proposed their main sources, e.g. sea-salt aerosol (SSA), oceanic biogenic activity, polar snow/ice, and volcanoes. Typhoons and other strong cyclonic activities (e.g. hurricanes) induce abrupt changes in different earth system processes, causing widespread destructive effects. However, the role of typhoons in regulating reactive bromine abundance and sources remains unexplored. Here, we report field observations of bromine oxide (BrO), a critical indicator of reactive bromine, on the Huaniao Island (HNI) in the East China Sea in July 2018. We observed high levels of BrO below 500 m with a daytime average of 9.7 ± 4.2 pptv and a peak value of ∼26 pptv under the influence of a typhoon. Our field measurements, supported by model simulations, suggest that the typhoon-induced drastic increase in wind speed amplifies the emission of SSA, significantly enhancing the activation of reactive bromine from SSA debromination. We also detected enhanced BrO mixing ratios under high NOx conditions (ppbv level) suggesting a potential pollution-induced mechanism of bromine release from SSA. Such elevated levels of atmospheric bromine noticeably increase ozone destruction by as much as ∼40% across the East China Sea. Considering the high frequency of cyclonic activity in the northern hemisphere, reactive bromine chemistry is expected to play a more important role than previously thought in affecting coastal air quality and atmospheric oxidation capacity. We suggest that models need to consider the hitherto overlooked typhoon- and pollution-mediated increase in reactive bromine levels when assessing the synergic effects of cyclonic activities on the earth system.

Mechanistic study on photochemical generation of I•/I2•- radicals in coastal atmospheric aqueous aerosol

The reactive iodine species may exhibit significant impacts on many global atmospheric issues and the I^•/I₂^•- radicals play key roles for inducing the formation of these reactive iodine species. However, the current understanding on the formation of I^•/I₂^•- radicals in atmospheric aqueous aerosol is still quite limited. The results reported herein suggest that I^•/I₂^•- can be produced simultaneously in aqueous aerosol by several sunlight-driven photochemical pathways including direct photo-dissociation of soluble organic iodine (SOI) at rates of 0.10-1.34 × 10^-9 M ns^-1 and 0.99-5.68 × 10^-7 M μs^-1, ^•OH-mediated oxidation of I^- at 0.03-1.41 × 10^-8 M ns^-1 and 0.05-4.10 × 10^-6 M μs^-1, and ³DOM^⁎-induced oxidation of I^- at 1.57-1.65 × 10^-9 M ns^-1 and 0.99-5.68 × 10^-7 M μs^-1 for generation of I^• and I₂^•-, respectively. Meanwhile, the pathway of e_aq^--initiated stepwise reduction of IO₃^- to I_2(aq) and further photolyzed into I^• plays negligible role in formation of I^•/I₂^•- due to the low reaction rates and severe quenching effect of e_aq^- by dissolved O₂. Our work presented the new data on mechanism and kinetics for comprehensive elucidation of I^•/I₂^•- formation in coastal atmospheric aqueous aerosol and would help to better understand the transformation mechanism of iodine species, pathways of iodine cycling and the associated environmental impacts involving atmospheric reactive iodine radicals.

Enhanced Chlorine and Bromine Atom Activation by Hydrolysis of Halogen Nitrates from Marine Aerosols at Polluted Coastal Areas

Detailed multiphase chemistry box model studies are carried out, investigating halogen radical activation at polluted coastal areas. Simulations are performed for a nonpermanent cloud and a cloud-free scenario and reveal that ClNO₂ photolysis and ICl photolysis are crucial for gas-phase Cl atom activation. In the cloud scenario, the integrated ClNO₂ and ICl photolysis rates are 3.7 × 10⁷ and 3.1 × 10⁷ molecules cm^-3 s^-1. In the cloud-free scenario, the integrated ClNO₂ and ICl photolysis rates are 8.1 × 10⁷ and 3.6 × 10⁷ molecules cm^-3 s^-1. The simulations show larger contributions of ClNO₂ photolysis in the morning and higher ones of ICl photolysis during afternoon. Throughout the simulation, average contributions to Cl atom activation in the cloud and cloud-free scenarios by ClNO₂ photolysis are 42% and 62% and by ICl photolysis 35% and 28%, respectively. ICl is formed through an aqueous-phase reaction of HOI with chloride. Two thirds of the formed ICl is released into the gas phase. The residual third reacts with bromide, creating IBr. Overall, the simulations emphasize the crucial role of INO₃ hydrolysis for Cl and Br atom activation in polluted coastal areas. Therefore, it needs to be considered in chemical transport models to improve air quality predictions.

Phototransformation of Plastic Containing Brominated Flame Retardants: Enhanced Fragmentation and Release of Photoproducts to Water and Air

Increasing attention is being paid to the environmental fate and impact of plastics and their additives under sunlight exposure. We evaluated the photodegradation of polystyrene (PS) films (∼100 μm) containing brominated flame retardants (BFRs): decabromodiphenylether (BDE-209), tetrabromobisphenol A (TBBPA), and tetrabromobisphenol A-bis (2.3-dibromopropylether) (TBBPA-DBPE). Irradiations were performed in a solar simulator and outdoors. Infrared (IR) analyses indicated an acceleration of the photooxidation rate of fire-retarded PS films compared to pure PS with an enhancement factor of 7 for TBBPA-DBPE and TBBPA, and 10 for BDE-209. The accelerating effect was found to be correlated with the quantum yield for BFR photodegradation and its absorbance in the PS films. The presence of BFRs also modified the PS photooxidation mechanism and resulted in the formation of 14 brominated photoproducts via bromination and oxidation of PS. Furthermore, a drastic increase in chain scissions and loss of molecular weight was revealed by size exclusion chromatography. This enhanced degradation of PS led to significant leaching (15%) of oxidation products from PS films after immersion in water, and to the gas-phase emission of several volatile brominated products. Our findings suggest that fire-retarded plastics may be a source of potentially hazardous contaminants when exposed to sunlight.