Satellite-Based Emission Estimates of Tropospheric Bromine During Arctic Spring in the GEOS-Chem Model

During polar spring periods of elevated tropospheric bromine, referred to as bromine explosion events, are associated with near-complete removal of surface ozone. The satellite-based Ozone Monitoring Instrument (OMI) provides total column measurements of bromine monoxide (BrO) with daily, global coverage. This study estimates springtime bromine emissions over the Arctic using OMI retrievals of BrO in combination with the GEOS-Chem (version 12.0.1) model. Hotspots of BrO, likely connected to bromine explosions events, are identified based on the difference between OMI column BrO and GEOS-Chem simulations without a polar bromine source. Since total column BrO in GEOS-Chem is globally biased low with respect to the OMI retrievals, we specify a statistical bias threshold to define tropospheric hotspots of BrO and estimate lower limits for the missing tropospheric bromine. The daily flux of molecular bromine (Br2) is calculated based on the modeled lower tropospheric lifetime of inorganic bromine and the partitioning of bromine species into BrO at OMI overpass time. Following the application of Arctic emissions in GEOS-Chem, we successfully model the OMI-based tropospheric hotspots of BrO and simulate periods of isolated, significant (i.e., > 20 ppb) surface ozone loss with respect to standard simulations, but we do not fully capture the low ozone observed at Arctic surface stations. We will explore the application of our emission scheme in the GEOS Composition Forecast (GEOS-CF) model, which is run daily by the NASA Global Modeling and Assimilation Office to provide daily five-day forecasts of atmospheric composition.