Development of an OMI-Based Tropospheric Bromine Monoxide (BrO) Product and Implications for Missing Sources of Reactive Bromine in GEOS-Chem

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. In this study, we use OMI observations of BrO in combination with the GEOS-Chem chemical transport model to further investigate the influence of halogens on the oxidative capacity of troposphere. In the troposphere, the distribution of brominated compounds is variable and significant uncertainties remain in the chemical processes governing the sources and sinks of reactive bromine species. However, the stratospheric burden of bromine is well represented by the emission scheme of brominated source gases in GEOS-Chem. As a result, we use GEOS-Chem simulated stratospheric columns of BrO to separate the tropospheric signal of BrO from the OMI total column measurements. The resulting tropospheric BrO columns are used to identify seasonal and regional anomalies in tropospheric BrO not currently represented in GEOS-Chem. In particular, periods of elevated tropospheric BrO during polar spring are observable by OMI, and past studies have connected these so-called “bromine explosion” events to near complete removal of surface ozone. Due to significant uncertainties in the springtime polar source of reactive bromine, many global models, including GEOS-Chem, do not simulate these tropospheric ozone depletion events. Consequently, OMI-based tropospheric columns of BrO are useful tool for investigating the impact of bromine explosion events on tropospheric ozone depletion episodes as well as background air quality.