Evaluating and Improving Arctic Ozone Chemistry in an Atmospheric Model

The Arctic, though geographically remote, interests scientists because of the air-sea interactions that govern the composition of the atmosphere (Knepp et al. 2010). These interactions arestronglyinfluenced by sea ice. Arctic sea ice extent is decreasing and at an accelerated rate. Between 1979 and 2006, it is estimated the sea ice extent at the end of the melting season decreased 9.1% per decade (Stroeve et al. 2007). These changes have large implications for global temperature, air-sea exchange fluxes, and atmospheric chemistry. Sea ice is a source of reactive halogens, particularly bromine radicals and changes to sea ice can therefore impact tropospheric ozone concentrations. We see these changes most abundantly during the springtime when reactive halogens like bromine monoxide (BrO) deplete ozone to near-zero levels. Ozone is the primary precursor to the atmospheric oxidizing agent – the hydroxyl radical (OH) – which removes harmful pollutants from the air. Thus, the loss of ozone can affect the oxidation capacity of the atmosphere. As climate changes, it is important to understand and predict the effects of changing sea ice on Arctic atmospheric chemistry. In this work, we assess the ability of a current global model, GEOS-Chem, to predict ozone and BrO concentrations over the Arctic Ocean compared to a new dataset of ozone and BrO concentrations collected over Arctic sea ice. We quantify the performance of two model versions and discuss the processes that might further improve the model.