Comparison of model and ground observations finds snowpack and blowing snow 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 models studies suggest that halogens are emitted to the atmosphere from snowpack and reactions on wind-blown snow. The relative importance of snowpack and blowing snow sources is still debated, both at local scales and regionally throughout the Arctic. To understand 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 mechanism increases BrO by providing more surface area for reactive bromine recycling. The snowpack mechanism led to increased BrO across the Arctic Ocean with maximum production in coastal regions, whereas the blowing snow mechanism increases BrO in specific areas due to high surface windspeeds. 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.

Tropospheric Bromine Monoxide Vertical Profiles Retrieved Across the Alaskan Arctic in Springtime

“…Chemical modelling can be particularly useful to study reactive bromine source mechanisms along with specific multiphase reactions (e.g. Marelle et al, 2021;Ahmed et al, 2022;Swanson et al, 2022;Wang and Pratt, 2017). However, as noted in Wang and Pratt (2017), there are few vertically (and horizontally) resolved observations that can be used to evaluate the modelling of different halogen compounds, making observations that can fill this knowledge gap particularly important.…”

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

“…Recent modeling efforts have been most successful in reproducing the seasonal cycle of SSA mass concentrations observed at multiple polar sites with a blowing snow source and have found that blowing snow is the dominant source of SSA in polar regions during winter and spring (Huang & Jaeglé, 2017;Rhodes et al, 2017). Several studies have proposed that snow-sourced SSA likely plays an important role in polar tropospheric ozone and halogen chemistry through the release of active bromine in polar spring contributing to ozone depletion events (ODEs) (Choi et al, 2018;Huang et al, 2020;Kalnajs et al, 2013;Marelle et al, 2021;Swanson et al, 2022;Yang et al, 2010).…”