Balloon-borne stratospheric vertical profiling of carbonyl sulfide and evaluation of ozone scrubbing materials

Abstract. Carbonyl sulfide (COS) is a low abundance atmospheric trace gas that has a tropospheric lifetime of 2–2.5 years, allowing it to reach the stratosphere, where it undergoes photolysis and reactions with ⋅OH and O⋅ radicals, generating precursors of stratospheric aerosols. Vertical profiling of COS has rarely been realised, especially for stratospheric observations. In this study, we introduce a new technique for continuous and discrete vertical profiling of COS based on the analysis of air samples collected by AirCore, the LIghtweight Stratospheric Air (LISA) sampler, and its scaled-up version BigLISA, in three campaigns in Trainou (2019), Kiruna (2021) and Sodankylä (2023) using a Quantum Cascade Laser Spectrometer (QCLS). To eliminate potential COS measurement biases, we have investigated the efficiency of different scrubbers based on cotton and squalene for removing ozone (O3) and assessed their potential impacts on COS measurement. Furthermore, we examined the influence of different inlet configurations and O3 scrubbers on the retrieved COS profiles, and found no significant impact within the uncertainties. We found that the differences with the averaged profiles obtained from the Atmospheric Chemistry Experiment – Fourier Transform Spectrometer (ACE-FTS) and the measured AirCore profiles and LISA samples were less than 10 % (±50 ppt) at both mid and polar latitudes. Differences between our observations and COS observations from the SPectromètre InfraRouge d'Absorption à Lasers Embarqués (SPIRALE) ranged from 10 % to 15 %, with both methods showing similar COS trends over altitude. Moreover, we found squalene-based scrubbers to be suitable for quantitative O3 removal. Both AirCore and the LISA samplers are lightweight and suitable for routine balloon-borne COS profiling, providing useful observations for stratospheric research and validation of COS retrievals from remote sensing techniques.