Investigating Polar Tropospheric Ozone with Novel BrO and IO Retrievals from Pandoras

Tropospheric and stratospheric ozone variability plays a critical role in controlling the polar radiation budget. Although the factors influencing stratospheric ozone variation are quite well researched, tropospheric and near-surface ozone are subject to both dynamical and photochemical constraints that are still poorly understood. Measurements from a Thermo Scientific TEI-49i in-situ ozone analyzer at the Polar Environment Atmospheric Research Laboratory (PEARL) at Eureka, Nunavut, Canada (80.05°N, 86.42°W) show that surface ozone in the Arctic is characterized by two major annual depletion events: (1) a primary depletion which occurs during the springtime following polar sunrise, and has been attributed to enhancements of BrO (bromine explosion events), as well as (2) a secondary depletion which occurs in the late summer and early fall period. The PEARL MAX-DOAS (Multi-Axis Differential Optical Absorption Spectroscopy) ultraviolet (UV)-visible Ground-Based Spectrometer (PEARL-GBS) results show tropospheric BrO enhancements correlated with periods of reduced ozone concentrations. Additionally, we also use several UV-visible Pandora spectrometers affiliated with the Pandonia Global Network (PGN) to evaluate the feasibility of retrieving BrO and IO, which are not currently among the standard PGN products. We present here preliminary results of polar Pandora BrO and IO retrievals and investigate the potential link between summertime IO and late summer ozone depletions detected at Eureka. For this investigation, we use the MAX-DOAS measurements made by three Pandora instruments: Pandora #144 which was located at the PEARL Ridge Lab from 2019-2023, Pandora #280 located at the Eureka 0-Altitude PEARL Auxiliary Laboratory (0PAL) since 2024, and Pandora #152 located at the Norwegian Polar Institute Sverdrup in Ny-Ålesund, Svalbard (78.92°N, 11.93°E) since 2019. We retrieve BrO and IO from the Pandora spectra and find good agreement between Pandora and PEARL-GBS BrO dSCDs (Differential Slant Column Densities). Although measured enhancements of BrO from the Eureka instruments coincide with periods of springtime reduced surface ozone, this is not as evident for the IO results in the context of the summer ozone depletions. We demonstrate the capability of using the Pandora instruments to retrieve these halogen species with MAX-DOAS measurements. These Pandora retrieval methods for BrO and IO will allow for further study of the role of these trace gases in the polar tropospheric ozone cycle.