Impacts of Particle Composition and NOx on the Vertical Distribution of Reactive Bromine in the Arctic Troposphere

The polar spring is marked by periods of sustained atmospheric bromine chemistry in the Arctic boundary layer, which are implicated in widespread ozone depletion events (ODEs) and altered oxidation of atmospheric pollutants. While this atmospheric bromine originates in the snowpack, aerosol particles play a crucial role in sustaining enhanced mole fractions of bromine-containing trace gases aloft, away from the snowpack surface. While aerosol particles are necessary to observe this bromine chemistry aloft, the presence of aerosols aloft is not by itself sufficient to observe lofted air layers of bromine-containing trace gases. In particular, the influence of variations in particle composition, particle pH, and surface area concentrations on bromine-containing trace gas mole fractions aloft remains unclear. To explore these impacts, we used 1-D chemical modelling in conjunction with measured vertical profiles of BrO and ozone to examine the factors controlling the propagation of bromine-containing trace gases aloft. We find aerosol bromide content to be more determinative of bromine-containing trace gas mixing ratios aloft than aerosol particle surface area concentrations. The role of nitrogen oxides (NO_x) is also discussed.