Multiphase Reactive Bromine Chemistry during Late Spring in the Arctic: Measurements of Gases, Particles, and Snow

Abstract

Bromine radicals (Br•) cause ozone depletion and mercury deposition in the Arctic atmospheric boundary layer, following Polar sunrise. These Br radicals are primarily formed by the photolysis of molecular bromine (Br 2 ), which is photochemically produced in the snowpack. Recently, it was shown that bromine monoxide (BrO•), formed from the reaction of Br• with ozone, is episodically present until the onset of snowmelt in late Arctic spring. To examine the drivers of this late spring shutdown of reactive bromine chemistry, the gases Br 2 , HOBr, BrO, and BrCl were continuously monitored using chemical ionization mass spectrometry during the spring (March−May 2016) near Utqiagvik, Alaska. On May 10th, all four reactive bromine species fell below levels of detection at the same time that air temperature increased above 0 °C, surface albedo decreased, and snowmelt onset was observed. Prior to the cessation of atmospheric bromine chemistry, local surface snow samples in early May became significantly enriched in bromide, likely due to the slowdown of reactive bromine recycling with continued deposition but decreased emissions from the snowpack. Particulate bromide concentrations were not sufficient to explain the quantities of reactive bromine gases observed and decreased upon snowmelt. Low wind speeds during the weeks preceding the cessation of reactive bromine chemistry point to the lack of a contribution to bromine chemistry from blowing snow. Together, these results further highlight the significance of the surface snowpack in multiphase bromine recycling with important implications as the melt season arrives earlier due to climate change.

Implications of Snowpack Reactive Bromine Production for Arctic Ice Core Bromine Preservation

“…We implemented a snowpack bromine emission scheme into a global chemical transport model based on previous 1D and 3D modeling work (Swanson et al, 2022;Thomas et al, 2011;Toyota et al, 2011Toyota et al, , 2014. Unlike previous global models, our model explicitly tracked snow bromide in surface skin layer, shut down bromine emissions when surface melting occurs (Burd et al, 2017;Jeong et al, 2022), and separately represented the deposition-driven bromine recycling at the surface skin layer and the photochemistry-driven deeper snow reactive bromine production.…”

“…Snowpack bromine emissions are an important local source of reactive bromine over snow covered regions and are needed to explain spring Arctic ODEs (Swanson et al., 2022; Jeong et al., 2022, etc.). In contrast, loss of bromine from the snow has been considered negligible in the interpretation of long‐term ice core bromine trends (Vallelonga et al., 2021).…”

Airborne Observations Constrain Heterogeneous Nitrogen and Halogen Chemistry on Tropospheric and Stratospheric Biomass Burning Aerosol

“…When considering only observations in Figure 2a, used to determine γ (N 2 O 5 ), the median is 0.77. Previous field comparisons have shown that parameterized φ (ClNO 2 ) is likely an upper limit to actual values (McDuffie et al., 2018a), which may, in part, be caused by the assumption that chloride is homogeneously distributed across surface area (Jeong et al., 2023; McNamara et al., 2020; Royer et al., 2021). Therefore, the derived γ (N 2 O 5 ) is a lower limit range of 0.2–3.6 × 10 −3 .…”

Application of Satellite‐Based Detections of Arctic Bromine Explosion Events Within GEOS‐Chem

“…Similarly, running the simulation through June verifies that the detection of BrO TH ends in summer when snowmelt is expected to inhibit the propagation of bromine explosion events (Burd et al, 2017;Jeong et al, 2022). The ability of the ABr simulations to represent BrO TH is assessed in Section 3.3.1, in Section 3.3.2 modeled BrO columns and surface O 3 levels are evaluated against measurements collected by instruments onboard O-Buoys, and simulations of surface O 3 over the Arctic are discussed in Section 3.3.3.…”