Abstract
Abstract. Activated chlorine compounds in the polar winter stratosphere drive catalytic cycles that deplete ozone and methane, whose abundances are highly relevant to the evolution of global climate. The present work introduces a novel dataset of in situ measurements of relevant chlorine species in the lowermost Arctic stratosphere from the aircraft mission POLSTRACC–GW-LCYCLE–SALSA during winter 2015/2016. The major stages of chemical evolution of the lower polar vortex are presented in a consistent series of high-resolution mass spectrometric observations of HCl and ClONO2. Simultaneous measurements of CFC-12 are used to derive total inorganic chlorine (Cly) and active chlorine (ClOx). The new data highlight an altitude dependence of the pathway for chlorine deactivation in the lowermost vortex with HCl dominating below the 380 K isentropic surface and ClONO2 prevailing above. Further, we show that the Chemical Lagrangian Model of the Stratosphere (CLaMS) is generally able to reproduce the chemical evolution of the lower polar vortex chlorine budget, except for a bias in HCl concentrations. The model is used to relate local measurements to the vortex-wide evolution. The results are aimed at fostering our understanding of the climate impact of chlorine chemistry, providing new observational data to complement satellite data and assess model performance in the climate-sensitive upper troposphere and lower stratosphere region.
Highlights
Understanding the processes that affect the abundance of climate-relevant gases in the Arctic polar upper troposphere and lower stratosphere (UTLS) is crucial for a reliable estimation of their current and future impact on the radiation budget and on global climate
All of the chlorine species that contribute to this reaction are summarized under the term “active chlorine”, which is abbreviated as ClOx and comprises Cl, Cl2, ClO, ClOOCl, OClO and HOCl
The evolution of inorganic chlorine partitioning in the lowermost Arctic polar vortex over a period of 3 months is assessed by means of daily statistics, which is performed by calculating averages, standard deviation and quantiles from all vortex air data points during individual research flights in order to get a reasonable statistical sample size
Summary
Understanding the processes that affect the abundance of climate-relevant gases in the Arctic polar upper troposphere and lower stratosphere (UTLS) is crucial for a reliable estimation of their current and future impact on the radiation budget and on global climate. Polar stratospheric clouds (PSCs) play a crucial role in ozone depletion, as they provide a surface for the heterogeneous reactions that produce active chlorine from the reservoir species (Crutzen and Arnold, 1986; Drdla and Müller, 2012). As sunlight returns towards spring, photochemical reactions are initiated that lead to chlorine activation and to the formation of the ozone hole In the Northern Hemisphere, even the sign of change is undetermined This is the consequence of unresolved transport of ozone and counteracting effects from catalytic depletion and stratospheric cooling during climate change, where some transport and chemical processes may not have been implemented into the models in complete detail. A novel approach of threedimensional visualization of gravity waves from remote tomographic sampling with the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) has been presented by Krisch et al (2017), while Johansson et al (2018) examined how the same instrument consistently fills the gap between high-coverage spaceborne sampling and accurate high-resolution in situ measurements. Krause et al (2018) used chemical tracers to reveal the influence of mixing at the lower vortex edge on the age spectrum of the air
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