Long-term observations of halogen oxides in the Arctic: project overview and first results

Halogen chemistry is a central element of tropospheric ozone depletion events (ODEs) during polar spring. However, key processes such as source mechanisms of reactive halogen species, their transport, and interhalogen interactions are still not fully understood. Further, a quickly changing Arctic climate is expected to have a strong impact on halogen activation and ODEs, but more research is needed to make meaningful predictions about these changes.We deployed a Long-Path Differential Optical Absorption Spectroscopy (LP-DOAS) instrument in Utqiagvik (formerly Barrow), Alaska, in December 2023. The instrument was originally purpose-built for its previous deployment at the German research station Neumayer, Antarctica, where it operated successfully for more than two years (Nasse, 2019). In the Arctic, seasonal atmospheric transport and the township’s proximity to the observation site will lead to a larger anthropogenic influence by air pollution. Also, the different climatic conditions are likely to lead to further insights into the complex interactions between halogens and other trace gases, such as NO2.To improve the data quality, the instrumental set-up was extensively tested and optimised accordingly using the knowledge gained from the previous campaign in Antarctica. An overview of the instrument characteristics as well as the project outline will be presented. Moreover, first results of the LP-DOAS data will be shown focusing on data quality and data analysis.