Application of Satellite‐Based Detections of Arctic Bromine Explosion Events Within GEOS‐Chem.

During polar spring, periods of elevated tropospheric bromine drive near complete removal of surface ozone. These events impact the tropospheric oxidative capacity and are an area of active research with multiple approaches for representing the underlying processes in global models. We present a method for parameterizing emissions of molecular bromine (Br2) over the Arctic using satellite retrievals of bromine monoxide (BrO) from the Ozone Monitoring Instrument (OMI). OMI retrieves column BrO with daily near global coverage, and we use the GEOS‐Chem chemical mechanism, run online within the Goddard Earth Observing System Earth System Model to identify hotspots of BrO likely associated with polar processes. To account for uncertainties in modeling background BrO, hotspots are only identified where the difference between OMI and modeled columns exceeds a statistical threshold. The resulting hotspot columns are a lower‐limit for the portion of OMI BrO attributable to bromine explosion events. While these hotspots are correlated with BrO measured in the lower troposphere over the Arctic Ocean, a case study of missing detections of near‐surface BrO is identified. Daily flux of Br2 is estimated from hotspot columns of BrO using internal model parameters. When the emissions are applied, BrO hotspots are modeled with a 5% low bias. The sensitivity of the resulting ozone simulations to the treatment of background uncertainties in the BrO column is demonstrated. While periods of isolated, large (>50%) decreases in surface ozone are modeled, this technique does not simulate the low ozone observed at coastal stations and consistently underestimates ozone loss during March. Plain Language Summary: During polar spring, high levels of bromine‐containing molecules drive near complete removal of surface ozone (O3), impacting the chemistry of the troposphere and the biological uptake of mercury. Global models currently have multiple mechanisms for representing the underlying processes that produce brominated molecules in polar regions. We estimate molecular bromine (Br2) emissions from measurements of bromine monoxide (BrO) collected over the Arctic by a satellite instrument. An atmospheric model, run without polar emissions of Br2, is used to estimate how much of the satellite BrO signal is due to background processes in the stratosphere and troposphere and isolate the portion of the signal likely associated with Arctic emissions. We account for uncertainties in the model representation of background BrO using a statistical threshold. Because of the catalytic nature of bromine‐mediated ozone depletion, we focus our initial efforts on developing a lower‐limit estimate of Arctic emissions. The amount of BrO attributed to polar processes and the resulting impact on O3 are sensitive to the magnitude of the statistical threshold, with a better representation of surface O3 achieved with a lower threshold. While the satellite‐based emissions result in periodic decreases in surface O3 in late spring, modeled O3 is consistently high with respect to observations, particularly during early spring. Key Points: BrO hotspots are isolated from satellite signals using modeled columns of BrO and a bias threshold to account for model uncertaintiesWe estimate Arctic Br2 emissions from BrO signals and demonstrate the sensitivity of modeled O3 to the BrO hotspot detection thresholdSimulations with satellite‐based Br2 emissions overestimate springtime Arctic surface O3 with few ozone depleting events modeled in March [ABSTRACT FROM AUTHOR]