Comparison of model and ground observations finds snowpack and blowing snow aerosols both contribute to Arctic tropospheric reactive bromine

Abstract

Abstract. Reactive halogens play a prominent role in the atmospheric chemistry of the Arctic during springtime. Field measurements and modeling studies suggest that halogens are emitted into the atmosphere from snowpack and reactions on wind-blown snow-sourced aerosols. The relative importance of snowpack and blowing snow sources is still debated, both at local scales and regionally throughout the Arctic. To understand the implications of these halogen sources on a pan-Arctic scale, we simulate Arctic reactive bromine chemistry in the atmospheric chemical transport model GEOS-Chem. Two mechanisms are included: (1) a blowing snow sea salt aerosol formation mechanism and (2) a snowpack mechanism assuming uniform molecular bromine production from all snow surfaces. We compare simulations including neither mechanism, each mechanism individually, and both mechanisms to examine conditions where one process may dominate or the mechanisms may interact. We compare the models using these mechanisms to observations of bromine monoxide (BrO) derived from multiple-axis differential optical absorption spectroscopy (MAX-DOAS) instruments on O-Buoy platforms on the sea ice and at a coastal site in Utqiaġvik, Alaska, during spring 2015. Model estimations of hourly and monthly average BrO are improved by assuming a constant yield of 0.1 % molecular bromine from all snowpack surfaces on ozone deposition. The blowing snow aerosol mechanism increases modeled BrO by providing more bromide-rich aerosol surface area for reactive bromine recycling. The snowpack mechanism led to increased model BrO across the Arctic Ocean with maximum production in coastal regions, whereas the blowing snow aerosol mechanism increases BrO in specific areas due to high surface wind speeds. Our uniform snowpack source has a greater impact on BrO mixing ratios than the blowing snow source. Model results best replicate several features of BrO observations during spring 2015 when using both mechanisms in conjunction, adding evidence that these mechanisms are both active during the Arctic spring. Extending our transport model throughout the entire year leads to predictions of enhanced fall BrO that are not supported by observations.

Impact of Changing Arctic Sea Ice Extent, Sea Ice Age, and Snow Depth on Sea Salt Aerosol From Blowing Snow and the Open Ocean for 1980–2017

“…SSA influence radiative forcing and therefore climate both directly by absorbing and scattering sunlight and indirectly by modifying the reflectivity, emissivity, lifetime, and extent of clouds (DeMott et al., 2016; O’Dowd et al., 1997; Struthers et al., 2011). Furthermore, SSA likely play an important role in polar tropospheric ozone and halogen chemistry through the release of active bromine in polar spring which contributes to ozone depletion events (ODEs) (e.g., Choi et al., 2018; Huang et al., 2020; Kalnajs et al., 2013; Marelle et al., 2021; Swanson et al., 2022; Yang et al., 2010).…”

Arctic tropospheric ozone: assessment of current knowledge and model performance

“…1; Hermann et al, 2019). Some model studies were able to explain major depletion events in simulations by introducing the wind-induced release of bromine from the snowpack and have shown that both blowing snow and the snowpack are important sources of bromine during the spring (e.g., Yang et al, 2010;Toyota et al, 2011;Yang et al, 2020;Huang et al, 2020;Swanson et al, 2022). Figure 2 shows the vertical extent of low O 3 episodes observed by lidar at Eureka in northern Canada.…”

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

“…Hourly output of surface layer O 3 and profiles of BrO from GEOS-Chem simulations are sampled along the O-Buoy tracks at the closest time to each MAX-DOAS measurement. Columns of BrO 200m and BrO LT are determined from modeled profiles of BrO following the method presented by Swanson et al (2022). For each time step along the buoy track, partial columns of modeled BrO are calculated along the vertical resolution of the MAX-DOAS averaging kernels.…”

“…Columns of BrO 200m and BrO LT are determined from modeled profiles of BrO following the method presented by Swanson et al. (2022). For each time step along the buoy track, partial columns of modeled BrO are calculated along the vertical resolution of the MAX‐DOAS averaging kernels.…”

“…The surfaces considered include saline snowpacks over sea ice and land (Cao et al., 2014; Foster et al., 2001; Pratt et al., 2013) and sea salt aerosols generated by wind‐driven blowing snow (Frey et al., 2020; Huang et al., 2018), with multiple studies reporting direct observations of Br 2 above snowpacks (e.g., Custard et al., 2017; Pratt et al., 2013; Raso et al., 2017). The saline surfaces used to model the release of Br 2 are typically continental and sea ice snowpacks (Falk & Sinnhuber, 2018; Fernandez et al., 2019; Herrmann et al., 2021; Toyota et al., 2011) or sea salt aerosols from blowing snow (Huang et al., 2020; Yang et al., 2005, 2010; Zhao et al., 2016), and two recent modeling efforts have also represented bromine explosion events using a combination of snowpack and blowing snow source mechanisms (Marelle et al., 2021; Swanson et al., 2022). In both mechanisms, the Br − in sea water is frozen in sea ice and taken up by the snowpack or deposited by aerosols and trace gases (Domine et al., 2004).…”