Variability of bromine monoxide at Barrow, Alaska, over four halogen activation (March–May) seasons and at two on‐ice locations

Abstract

AbstractReactive halogens profoundly influence springtime Arctic atmospheric chemistry, but their relationship to sea ice and environmental conditions is not well understood. Multiple axis differential optical absorption spectroscopy measured bromine monoxide (BrO) at Barrow, Alaska, and at two Arctic Ocean buoys. For each season of Barrow measurements, we examined the air mass histories using back trajectory modeling and ice coverage maps. We find a weak positive linear correlation (R = 0.38) between half‐hourly BrO lower tropospheric vertical column densities (LT‐VCD) and time in first year sea ice (FYI) areas. These data show evidence of a nonlinear increase of LT‐VCD BrO with low‐average column in the absence of ice contact, with the column increasing and saturating at ice contact longer than ≈1.5 days. We find that trajectories arriving at Barrow are dominated by FYI area influence with little multiyear ice (MYI) area contact; therefore, this study cannot make any conclusions regarding MYI area influences on reactive halogen production. Contact with calculated potential frost flower influence is not correlated with BrO column (R = 0.04). At Barrow, annual averages of BrO column over the halogen activation season and time in FYI areas are highly correlated (R = 0.93, significant at 90% confidence), which is interpreted as an effect of interannual transport variability. At on‐ice locations, we observe a wide range of BrO LT‐VCDs, suggesting that while an air mass spending time in sea ice areas is required to observe significant BrO, sea ice contact alone does not imply high BrO, and other environmental controls are important.