Springtime Bromine Activation over Coastal and Inland Arctic Snowpacks

Abstract

With the return of sunlight in the polar spring, the snowpack serves as an effective source of molecular halogens to the Arctic boundary layer. Reactive bromine production and associated ozone depletion are typically associated with sea ice regions; however, the extent to which halogen chemistry occurs inland in coastal regions is unknown. During the March 2012 bromine, ozone, and mercury experiment (BROMEX), airborne nadir scanning differential optical absorption spectroscopy probed the spatial distribution of BrO over sea ice and tundra regions near Utqiagvik, Alaska. We observed enhanced BrO lower tropospheric vertical column densities (LT-VCDs) up to 200 km inland. Vertical profiles showed that BrO was located near the snowpack surface, consistent with prior studies of snowpack chemical composition showing bromide enrichment, which is indicative of deposition of gas-phase bromine species to the snowpack. Over nine flights across the Alaskan Arctic, the highest BrO LT-VCDs were observed over snow-covered tundra regions rather than sea ice regions, although the variability was large at all locations. Characterization of the response of observed BrO over northern Alaska to ozone conditions at Utqiagvik showed that regional BrO levels were highest during times when ozone mole fractions were decreasing, consistent with locally occurring chemical destruction of ozone by bromine chemistry. These findings suggest that, while bromine activation is most commonly associated with sea ice regions, inland tundra snowpacks enable the transport and recycling of reactive bromine, extending this halogen chemistry and its associated impacts further inland.

Snowpack measurements suggest role for multi-year sea ice regions in Arctic atmospheric bromine and chlorine chemistry

“…The Br -/Clratios presented in Figure 5 suggest the ability of terrestrial and MYI snowpacks to produce Br 2 should be accounted for in models. Airborne measurements of BrO 200 km inland by Peterson et al (2018) provide further evidence of the effectiveness of terrestrial snowpacks in producing reactive bromine. Given that the conditions for Br 2 production are most frequently observed in terrestrial snowpacks, it is likely those snowpacks will play an increasing role in Arctic boundary layer bromine chemistry as sea ice extent declines.…”

Evaluating the impact of blowing-snow sea salt aerosol on springtime BrO and O<sub>3</sub> in the Arctic

“…Domine et al (2004) estimate that frost flowers could account for 10 % of the observed surface snow salinity. The upward migration of brine is expected to be the dominant source of salinity for thin snow over sea ice (< 10-17 cm; Domine et al, 2004;Peterson et al, 2019). As the snow depth gets thicker, the salinity of surface snow decreases and the influence of atmospheric deposition likely becomes more important (Krnavek et al, 2012;Nandan et al, 2017).…”

Long-term time series of Arctic tropospheric BrO derived from UV–VIS satellite remote sensing and its relation to first-year sea ice

“…Although there are studies which try to model BrO plumes from their driving mechanisms (Falk and Sinnhuber, 2018;Seo et al, 2019b;Huang et al, 2020), the exact level of impact of each parameter on the formation of enhanced tropospheric BrO is uncertain. However, there is the general consensus that the potential sources of BrO plumes are (a) rich in sea salts and relatively cold (conditions occurring in potential frost flowers regions; Rankin et al, 2002;Kaleschke et al, 2004;Sander et al, 2006), (b) surfaces covered with liquid or frozen brine (Sander et al, 2006), (c) associated with blowing snow (Yang et al, 2008;Blechschmidt et al, 2016;Frey et al, 2020), and (d) surface snow packs (Pratt et al, 2013;Peterson et al, 2018) and young salty sea ice regions (Wagner et al, 2001;Simpson et al, 2007;Peterson et al, 2016). A pH lower than 6.5 is required for efficient bromine activation (Fickert et al, 1999;Halfacre et al, 2019).…”