A surface-stabilized ozonide triggers bromide oxidation at the aqueous solution-vapour interface

Abstract

Oxidation of bromide in aqueous environments initiates the formation of molecular halogen compounds, which is important for the global tropospheric ozone budget. In the aqueous bulk, oxidation of bromide by ozone involves a [Br•OOO−] complex as intermediate. Here we report liquid jet X-ray photoelectron spectroscopy measurements that provide direct experimental evidence for the ozonide and establish its propensity for the solution-vapour interface. Theoretical calculations support these findings, showing that water stabilizes the ozonide and lowers the energy of the transition state at neutral pH. Kinetic experiments confirm the dominance of the heterogeneous oxidation route established by this precursor at low, atmospherically relevant ozone concentrations. Taken together, our results provide a strong case of different reaction kinetics and mechanisms of reactions occurring at the aqueous phase-vapour interface compared with the bulk aqueous phase.

Modeling the Sources and Chemistry of Polar Tropospheric Halogens (Cl, Br, and I) Using the CAM‐Chem Global Chemistry‐Climate Model

“…Equivalent recycling reactions occur also on sea‐salt aerosols (Fernandez et al, ; McFiggans et al, ; Vogt et al, ). Some of these recycling processes are proposed to be controlled by ozone deposition with subsequent halide oxidation (Artiglia et al, ; Liao et al, ; Toyota et al, ). Unlike bromine and chlorine, the much smaller atmospheric iodine levels observed in the Arctic with respect to the Antarctic, results in a “polar iodine paradox,” which is not yet fully understood (Saiz‐Lopez & Blaszczak‐Boxe, ).…”

Microphysics of the aqueous bulk counters the water activity driven rate acceleration of bromide oxidation by ozone from 289–245 K

“…[39][40][41] Aqueous bulk bromide oxidation by ozone is relatively slow with a rate coefficient of $258 M À1 s À1 at 298 K. 32 Hunt et al showed that the observed Br 2 production resulting from this reaction system exceeded that expected from bulk aqueous production alone, and suggested a contribution from interfacial processes. 39 Other studies probing possibilities of additional interfacial processes corroborate this suggestion by Hunt et al [40][41][42][43] Oldridge and Abbatt, while monitoring Br 2 production, showed that the interfacial processes become signicant at atmospherically relevant low ozone concentrations. 40 Studies on the interfacial process indicate that this process proceeds via the formation of an adsorbed intermediate species on the surface of the observed system.…”

BrO and inferred Br<sub><i>y</i></sub> profiles over the western Pacific: relevance of inorganic bromine sources and a Br<sub><i>y</i></sub> minimum in the aged tropical tropopause layer

“…6 (and Table 5). However, recent laboratory observations of surfaceactive BrO − 3 (primary ozonide; Artiglia et al, 2017) also support the important role of O 3 reactive uptake for the heterogeneous recycling of gas-phase Br y , which is most relevant in the upper troposphere . The surface activity of the primary ozonide suggests that recycling of Br y to the gas phase may be in competition with bulk accommodation of HOBr and subsequent S(IV) chemistry, which would reduce the efficiency of Br y washout.…”

“…While excluding the SSA source from GEOS-Chem reproduces inferred Br y in the mid-FT, it does not show the increase in inferred Br y in the upper FT and convective TTL. Revisions to the ozone-induced source of HOBr from aerosol bromide at the air-water interface (Artiglia et al, 2017) -which is partic- In the TTL, GEOS-Chem (with and without the SSA source) shows some increase in BrO and Br y at the highest altitudes, but only after a minimum in the same region. CAM-Chem does not show this increase in the median, though the 95th percentile makes it transparent that elevated BrO is predicted in certain instances.…”