Satellite-Based Emission Estimates of Tropospheric Bromine During Arctic Spring and Impact on Surface Ozone

The OMI satellite instrument provides total column measurements of bromine monoxide (BrO) with daily global coverage. Reactive bromine compounds (Br and BrO) catalytically destroy ozone in both the stratosphere and troposphere. Periods of elevated tropospheric BrO during polar spring are observable by OMI. Past studies have connected these elevated bromine events to near complete removal of surface ozone as well as significant perturbations to polar NO_x (NO + NO₂) and HO_x (OH + HO₂) chemistry.

In this study, we use OMI observations of BrO in combination with the GEOS-Chem global model to develop a method for estimating tropospheric emissions of bromine during Arctic spring. Total column BrO is modeled in GEOS-Chem using a combined stratospheric and tropospheric chemical mechanism. We find that globally total column BrO in GEOS-Chem is low with respect to the OMI retrievals. Because the stratospheric burden of bromine is well represented in GEOS-Chem, a portion of this bias likely originates from uncertainties in the chemical partitioning of inorganic bromine in the lower stratosphere and free troposphere. We specify a bias threshold to define elevated tropospheric BrO events and estimate lower limits for the missing tropospheric bromine during Arctic spring. Additionally, we evaluate the ability of our emission scheme to capture surface observations of ozone and explore the impact of bromine explosion events on the Arctic oxidative capacity.