HCl and ClO in activated Arctic air; first retrieved vertical profiles from TELIS submillimetre limb spectra

The first profile retrieval results of the Terahertz and submillimeter Limb Sounder (TELIS) balloon instrument are presented. The spectra are recorded during a 13-h balloon flight on 24 January 2010 from Kiruna, Sweden. The TELIS instrument was mounted on the MIPAS-B2 gondola and shared this platform with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) and the mini- Differential Optical Absorption Spectroscopy (mini-DOAS) instruments. The flight took place within the Arctic vortex at an altitude of ≈34 km in chlorine activated air, and both active (ClO) and inactive chlorine (HCl) were measured over an altitude range of respectively ≈16–32 km and ≈10– 32 km. In this altitude range, the increase of ClO concentration levels during sunrise has been recorded with a temporal resolution of one minute. During the daytime equilibrium, a maximum ClO level of 2.1±0.3 ppbv has been observed at an altitude of 23.5 km. This equilibrium profile is validated against the ClO profile by the satellite instrument Microwave Limb Sounder (MLS) aboard EOS Aura. HCl profiles have been determined from two different isotopes – H35Cl and H37Cl – and are also validated againstMLS. The precision of all profiles is well below 0.01 ppbv and the overall accuracy is therefore governed by systematic effects. The total uncertainty of these effects is estimated to be maximal 0.3 ppbv for ClO around its peak value at 23.5 km during the daytime equilibrium, and for HCl it ranges from 0.05 to 0.4 ppbv, depending on altitude. In both cases the main uncertainty stems from a largely unknown non-linear response in the detector

Partitioning and budget of inorganic and organic chlorine species observed by MIPAS-B and TELIS in the Arctic in March 2011

The Arctic winter 2010/11 was characterized by a persisting vortex with extremely cold temperatures in the lower stratosphere above northern Scandinavia leading to a strong activation of chlorine compounds (ClOx) like Cl, Cl2, ClO, ClOOCl, OClO, and HOCl which rapidly destroyed ozone when sunlight returned after winter solstice. MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) and TELIS (Terahertz and submillimeter Limb Sounder) balloon measurements obtained in northern Sweden on 31 March 2011 inside the polar vortex have provided vertical profiles of inorganic and organic chlorine species as well as diurnal variations of ClO around sunrise over the whole altitude range in which chlorine is undergoing activation and deactivation. This flight was performed at the end of the winter during the last phase of ClOx deactivation. The complete inorganic and organic chlorine partitioning and budget in the stratosphere has been derived by combining MIPAS-B and TELIS simultaneously observed molecules. A total chlorine amount of 3.41 ± 0.30 ppbv is inferred from the measurements. This value is in line with previously carried out stratospheric observations confirming the slightly decreasing chlorine trend in the stratosphere. Observations are compared and discussed with the output of a multi-year simulation performed with the Chemistry Climate Model EMAC (ECHAM5/MESSy Atmospheric Chemistry). The simulated stratospheric total chlorine amount is in accordance with the MIPAS-B/TELIS observation taking into account the fact that some chlorine source gases and very short lived species are not included in the model

Validation of the vertical profiles of HCl over the wide range of the stratosphere to the lower thermosphere measured by SMILES

Hydrogen chloride (HCl) is the most abundant (more than 95 %) among inorganic chlorine compounds Cly in the stratosphere. The HCl molecule has been observed to obtain long-term quantitative estimations of total budget of the stratospheric anthropogenic chlorine compounds. In this study, we provided HCl vertical profiles at altitudes of 16–100 km using the superconducting submillimeter-wave limb-emission sounder (SMILES) from space. We used the SMILES Level-2 research product version 3.0.0. The period of the SMILES HCl observation was from October 12, 2009 to April 21, 2010, and the latitude coverage was 40S–65N. The average HCl vertical profile showed an increase with altitude up to the stratopause (~ 45 km), approximately constant values between the stratopause and the upper mesosphere (~ 80 km), and a decrease from the mesopause to the lower thermosphere (~ 100 km). This behavior was observed in the all latitude regions, and reproduced by the SD-WACCM model. We compared the SMILES HCl vertical profiles in the stratosphere and lower mesosphere with HCl profiles from MLS on the Aura satellite, as well as from ACE-FTS on SCISAT and from TELIS (balloon-borne). The TELIS observations were performed using the superconductive limb emission technique, as used by SMILES. The globally averaged vertical HCl profiles of SMILES well agreed with those of MLS and ACE-FTS within 0.25 and 0.2 ppbv between 20 and 40 km, respectively. The SMILES HCl concentration was smaller than those of MLS and ACE/FTS as the altitude increased from 40 km, and the difference was approximately 0.4–0.5 ppbv at 50–60 km. The difference between SMILES and TELIS HCl observations was about 0.3 ppbv in the polar winter region between 20 and 34 km, except near 26 km. SMILES HCl error sources that may cause discrepancies with the other observations are investigated by a theoretical error analysis. We calculated errors caused by the uncertainties of spectroscopic parameters, instrument functions, and atmospheric temperature profiles. The jacobian for the temperature explains the negative bias of the SMILES HCl concentration at 50–60 km. The HCl vertical profile from the middle troposphere to the lower thermosphere is reported for the first time from SMILES observations; the data quality is quantified by comparisons with other measurements and via theoretical error analysis

Validation of Stratospheric and Mesospheric Ozone Observed by SMILES from International Space Station

We observed ozone O3 in the vertical region between 250 and 0.0005 hPa (~ 12-96 km) using the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) on the Japanese Experiment Module (JEM) of the International Space Station (ISS) between 12 October 2009 and 21 April 2010. The new 4K superconducting heterodyne receiver technology of SMILES allowed us to obtain a one order of magnitude better signal-to-noise ratio for the O3 line observation compared to past spaceborne microwave instruments. The non-sun-synchronous orbit of the ISS allowed us to observe O3 at various local times. We assessed the quality of the vertical profiles of O3 in the 100-0.001 hPa (~ 16-90 km) region for the SMILES NICT Level 2 product version 2.1.5. The evaluation is based on four components: error analysis; internal comparisons of observations targeting three different instrumental setups for the same O3 625.371 GHz transition; internal comparisons of two different retrieval algorithms; and external comparisons for various local times with ozonesonde, satellite and balloon observations (ENVISAT/MIPAS, SCISAT/ACE-FTS, Odin/OSIRIS, Odin/SMR, Aura/MLS, TELIS). SMILES O3 data have an estimated absolute accuracy of better than 0.3 ppmv (3%) with a vertical resolution of 3-4 km over the 60 to 8 hPa range. The random error for a single measurement is better than the estimated systematic error, being less than 1, 2, and 7%, in the 40-1, 80-0.1, and 100-0.004 hPa pressure regions, respectively. SMILES O-3 abundance was 10-20% lower than all other satellite measurements at 8-0.1 hPa due to an error arising from uncertainties of the tangent point information and the gain calibration for the intensity of the spectrum. SMILES O3 from observation frequency Band-B had better accuracy than that from Band-A. A two month period is required to accumulate measurements covering 24 h in local time of O3 profile. However such a dataset can also contain variation due to dynamical, seasonal, and latitudinal effects

Stratospheric Water Vapour in the Tropics: Observations by Ground-Based Microwave Radiometry

This thesis reports on observations of tropical stratospheric water vapour by the ground-based microwave radiometer/spectrometer WaRAM2 in 2007. The 22GHz receiver is set up at Mérida Atmospheric Research Station on top of Pico Espejo, Venezuela (8°32'N, 71°03'W, 4765m above sea level). It is the only such sensor that continuously operates at tropical latitudes. The high altitude site is ideally suitable for microwave observations, because most tropospheric water vapour is located below the sensor. Water vapour plays a key role in middle atmospheric processes. Because of its large infrared resonance, it strongly participates in the radiative budget, both in terms of a greenhouse effect at lower altitudes and radiative cooling at higher altitudes. It is a source gas for the highly reactive hydroxyl radical, and exerts indirect effects on ozone destruction in the formation of polar stratospheric clouds. Due to its long lifetime, water vapour also serves as a dynamical tracer

Reconciliation of essential process parameters for an enhanced predictability of Arctic stratospheric ozone loss and its climate interactions

Significant reductions in stratospheric ozone occur inside the polar vortices each spring when chlorine radicals produced by heterogeneous reactions on cold particle surfaces in winter destroy ozone mainly in two catalytic cycles, the ClO dimer cycle and the ClO/BrO cycle. Chlorofluorocarbons (CFCs), which are responsible for most of the chlorine currently present in the stratosphere, have been banned by the Montreal Protocol and its amendments, and the ozone layer is predicted to recover to 1980 levels within the next few decades. During the same period, however, climate change is expected to alter the temperature, circulation patterns and chemical composition in the stratosphere, and possible geo-engineering ventures to mitigate climate change may lead to additional changes. To realistically predict the response of the ozone layer to such influences requires the correct representation of all relevant processes. The European project RECONCILE has comprehensively addressed remaining questions in the context of polar ozone depletion, with the objective to quantify the rates of some of the most relevant, yet still uncertain physical and chemical processes. To this end RECONCILE used a broad approach of laboratory experiments, two field missions in the Arctic winter 2009/10 employing the high altitude research aircraft M55-Geophysica and an extensive match ozone sonde campaign, as well as microphysical and chemical transport modelling and data assimilation. Some of the main outcomes of RECONCILE are as follows: (1) vortex meteorology: the 2009/10 Arctic winter was unusually cold at stratospheric levels during the six-week period from mid-December 2009 until the end of January 2010, with reduced transport and mixing across the polar vortex edge; polar vortex stability and how it is influenced by dynamic processes in the troposphere has led to unprecedented, synoptic-scale stratospheric regions with temperatures below the frost point; in these regions stratospheric ice clouds have been observed, extending over >106km2 during more than 3 weeks. (2) Particle microphysics: heterogeneous nucleation of nitric acid trihydrate (NAT) particles in the absence of ice has been unambiguously demonstrated; conversely, the synoptic scale ice clouds also appear to nucleate heterogeneously; a variety of possible heterogeneous nuclei has been characterised by chemical analysis of the non-volatile fraction of the background aerosol; substantial formation of solid particles and denitrification via their sedimentation has been observed and model parameterizations have been improved. (3) Chemistry: strong evidence has been found for significant chlorine activation not only on polar stratospheric clouds (PSCs) but also on cold binary aerosol; laboratory experiments and field data on the ClOOCl photolysis rate and other kinetic parameters have been shown to be consistent with an adequate degree of certainty; no evidence has been found that would support the existence of yet unknown chemical mechanisms making a significant contribution to polar ozone loss. (4) Global modelling: results from process studies have been implemented in a prognostic chemistry climate model (CCM); simulations with improved parameterisations of processes relevant for polar ozone depletion are evaluated against satellite data and other long term records using data assimilation and detrended fluctuation analysis. Finally, measurements and process studies within RECONCILE were also applied to the winter 2010/11, when special meteorological conditions led to the highest chemical ozone loss ever observed in the Arctic. In addition to quantifying the 2010/11 ozone loss and to understand its causes including possible connections to climate change, its impacts were addressed, such as changes in surface ultraviolet (UV) radiation in the densely populated northern mid-latitudes

Chlorine partitioning in the lowermost Arctic stratosphere during winter – an aircraft in situ measurement perspective

Die vorliegende Arbeit untersucht experimentell die Veränderungen der Verteilungen von anorganischen Chlor-Reservoirgasen und aktiven Chlorverbindungen in der polaren untersten Stratosphäre im kalten Winter 2015/2016. Obwohl die Emission langlebiger chlorhaltiger Stoffe durch weltweite Klimaabkommen erfolgreich unterbunden wurde, bleiben stratosphärische Chlorkonzentrationen noch auf Jahrzehnte hinaus erhöht. Chlorverbindungen haben einen bedeutenden Anteil am katalytischen polaren Ozonabbau im Winter und Frühling. Die globale Ozonschicht ist ein wichtiger Faktor für den Strahlungshaushalt der Atmosphäre. Änderungen können Einflüsse haben auf die thermische Struktur und Stabilität der stratosphärischen Schichtung und Zirkulation, auf das Strahlungsbudget der Erdoberfläche und damit auf die Oberflächentemperatur, und nicht zuletzt auf die Belastung von Organismen durch Ultraviolettstrahlung. Der Transport und der katalytische Abbau von stratosphärischem Ozon werden seit vielen Jahren untersucht. Gerade in der polaren untersten Stratosphäre, die durch Mischungsprozesse an der Tropopause beeinflusst ist, verbleiben jedoch große Unsicherheiten in Vorhersagemodellen bezüglich Ozon und seiner Wirkung. Die vorliegende Arbeit stellt für diese schwer zugängliche Region neue flugzeuggetragene In-situ-Messungen aus der POLSTRACC-Kampagne im Arktischen Winter 2015/2016 vor. Mit dem Forschungsflugzeug HALO wurde dabei der untere Rand des arktischen Polarwirbels von Dezember bis März beprobt. Im Rahmen dieser Arbeit wurde eine Kalibration des Massenspektrometers AIMS bezüglich HCl und ClONO2 entwickelt, welche die schnelle und gleichzeitige Messung dieser Reservoirgase ermöglicht. Für den Verlauf des Winters und Frühlings 2015/2016 konnte aus den flugzeuggetragenen Messungen die Verteilung von anorganischem Chlor in aktive und Reservoir-Spezies mit Hilfe der potenziellen Temperatur quasi-vertikal aufgelöst werden. Es stellt sich heraus, das Chloraktivierung unterhalb von 400 K potenzieller Temperatur nie vollständig erfolgt, anders als bei höheren potenziellen Temperaturen. Gegen Ende des Polarwinters folgt eine unterschiedliche Umverteilung von Chlor in die Reservoirgase: Die Rückgewinnung von HCl dominiert auf niedrigen Höhen, während darüber ClONO2 überwiegt, verursacht durch Konzentrationsgradienten der Reaktionspartner Stickoxide, Ozon und Methan in der untersten Stratosphäre. Dies wird erstmals in massenspektrometrischen In-situ-Messungen mit hoher räumlicher und zeitlicher Auflö- sung beobachtet. Ein Vergleich mit dem Chemie-Transport-Modell CLaMS zeigt eine mit Ausnahmen gute Übereinstimmung. Zudem geben die lokalen und zufälligen Flugzeugmessungen die allgemeine Entwicklung der Chlorverteilung im Polarwirbel gut wieder. Die hochaufgelösten und genauen Messungen können jedoch eine systematische Überschätzung von HCl im unteren polaren Wirbel im Modell nachweisen. Der beobachtete Fall von außergewöhnlich starker Chloraktivierung in der untersten Stratosphäre zeigt auf, wie wichtig es ist, chemische, mikrophysikalische und dynamische Prozesse von Chlorverbindungen in der oberen Troposphäre und unteren Stratosphäre physikalisch korrekt zu beschreiben, um die Klimaentwicklung dieser Regionen vorhersagen zu können. This thesis experimentally studies the partitioning of inorganic chlorine into active and reservoir species in the polar lowermost stratosphere in the cold Arctic winter 2015/2016. Despite the successful phase-out of further emissions of long-lived chlorine containing substances through worldwide climate agreements, elevated levels of chlorine will persist for decades in the stratosphere. Chlorine compounds are among the major substances for the catalytic depletion of ozone during winter and spring seasons. The global ozone layer is an important factor in the radiative energy budget of the atmosphere, and changes to it can impact the thermal structure and stability of the stratosphere, stratospheric circulation patterns, the surface radiative energy budget controlling surface temperature, and last but not least the stress to organisms through ultraviolet radiation. While transport of ozone in the stratosphere and its catalytic depletion have been investigated in the past decades, major uncertainties in the projection of future ozone and its impact remain, especially in the polar lowermost stratosphere. The present work addresses the challenging observation and accessibility of this remote area with novel airborne in situ measurements. The HALO aircraft performed the POLSTRACC campaign in the Arctic winter 2015/2016, sampling the lower edge of the Arctic polar vortex from December to March. For the AIMS mass spectrometer, this work describes the development of a calibration for HCl and ClONO2 which enables simultaneous, highly accurate and fast measurements of these chlorine reservoir species. Over the course of the winter and spring 2015/2016, the partitioning of inorganic chlorine into active and reservoir species could be resolved quasi-vertically by potential temperature. It is found that chlorine is never fully activated in the Arctic below 400 K potential temperature, unlike observations at higher temperatures. Repartitioning of chlorine into the reservoir species varies towards the end of the polar winter: the recovery of HCl is favoured on the lower levels, whereas ClONO2 is favoured on the higher levels, due to concentration gradients in the available reaction partners nitrogen oxides, ozone and methane in the lowermost stratosphere. For the first time, this is observed with mass spectrometric in situ measurements at high temporal and spatial resolution. A comparison to the chemistry transport model CLaMS shows good agreement, with some exceptions, and demonstrates that the local and random airborne observations well represent the overall evolution of chlorine partitioning in polar vortex airmasses. Yet, the high accuracy and resolution of the measurements enable the detection of a systematic high bias of HCl in the model in the lowermost polar vortex. An observation of exceptionally high active chlorine in the lowermost stratosphere highlights the importance of a physically correct representation of chemical, microphysical and dynamical processes of chlorine species in the upper troposphere and lower stratosphere in climate projections