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- Evaluating global emission inventories of biogenic bromocarbons (2013)
- Emissions of halogenated very short-lived substances (VSLS) are poorly constrained. However, their inclusion in global models is required to simulate a realistic inorganic bromine (Bry) loading in both the troposphere, where bromine chemistry perturbs global oxidising capacity, and in the stratosphere, where it is a major sink for ozone (O3). We have performed simulations using a 3-D chemical transport model (CTM) including three top-down and a single bottom-up derived emission inventory of the major brominated VSLS bromoform (CHBr3) and dibromomethane (CH2Br2). We perform the first concerted evaluation of these inventories, comparing both the magnitude and spatial distribution of emissions. For a quantitative evaluation of each inventory, model output is compared with independent long-term observations at National Oceanic and Atmospheric Administration (NOAA) ground-based stations and with aircraft observations made during the NSF (National Science Foundation) HIAPER Pole-to-Pole Observations (HIPPO) project. For CHBr3, the mean absolute deviation between model and surface observation ranges from 0.22 (38%) to 0.78 (115%) parts per trillion (ppt) in the tropics, depending on emission inventory. For CH2Br2, the range is 0.17 (24%) to 1.25 (167%) ppt. We also use aircraft observations made during the 2011 Stratospheric Ozone: Halogen Impacts in a Varying Atmosphere (SHIVA) campaign, in the tropical western Pacific. Here, the performance of the various inventories also varies significantly, but overall the CTM is able to reproduce observed CHBr3 well in the free troposphere using an inventory based on observed sea-to-air fluxes. Finally, we identify the range of uncertainty associated with these VSLS emission inventories on stratospheric bromine loading due to VSLS (BryVSLS). Our simulations show BryVSLS ranges from ~4.0 to 8.0 ppt depending on the inventory. We report an optimised estimate at the lower end of this range (~4 ppt) based on combining the CHBr3 and CH2Br2 inventories which give best agreement with the compilation of observations in the tropics.
- Untersuchung des Transports in der untersten Stratosphäre anhand von in-situ Messungen langlebiger Spurengase (2005)
- Im Rahmen des Projektes SPURT (Spurenstofftransport in der Tropopausenregion) als Teil des deutschen Atmosphärenforschungsprogramms AFO 2000 wurden bei 8 Messkampagnen mit insgesamt 36 Flügen innerhalb eines Beobachtungszeitraums von zwei Jahren (Nov. 2001 bis Juli 2003) Spurengasmessungen in dem Breitenbereich zwischen 35°N und 75°N durchgeführt. Für die Messungen der Spurengase N2O, F12, SF6, H2 und CO wurde der vollautomatisierte in-situ GC (Gaschromatograph) GhOST II (Gas Chromatograph for the Observation of Stratospheric Tracers) entwickelt und eingesetzt. Das Ziel dieser Messungen war die Untersuchung der jahreszeitlichen Variabilität der Spurengase in der oberen Troposphäre und untersten Stratosphäre (UT/LMS: Upper Troposphere/Lowermost Stratosphere), um die Transport- und Austauschprozesse in der Tropopausenregion besser zu verstehen. Zur Untersuchung von Transport und Mischung in der UT/LMS wurden die Rückwärtstrajektorien entlang der Flugpfade, die Verteilungen der Tracer N2O, F12, SF6, CO und CO2 (MPI für Chemie in Mainz), die Tracer/Tracer-Korrelationen N2O/F12, N2O/O3 F12/O3 und SF6/O3 und die Verteilungen des aus SF6-Messungen berechnete mittlere Alters der Luft herangezogen. Zusätzlich wurden die simultanen Messungen der beiden Alterstracer CO2 und SF6 genutzt, um die Propagation der Amplitude des troposphärischen CO2-Jahresgangs in die LMS zu bestimmen und daraus mit Hilfe eines empirischen Altersspektrums den Eintrag und die mittlere Transportzeit aus der Troposphäre in die unterste Stratosphäre zu quantifizieren. Grundsätzlich muss die LMS in zwei Bereiche eingeteilt werden – die Übergangsschicht („tropopause following layer“) bis etwa 20-30 K über der potentiellen Temperatur der lokalen Tropopause [Hoor et al., 2004] und die freie LMS oberhalb dieser Schicht. Als wesentliche Unterscheidungsmerkmale beider Bereiche wird die mittlere Transportzeit des Eintrags troposphärischer Luft identifiziert. Aus Trajektorienuntersuchungen und Tracerverteilungen (Kap. 3.4) kann gezeigt werden, dass der Transport in die Übergangsschicht und die Mischungsprozesse in diesem Bereich auf der Zeitskala der mesoskaligen troposphärischen Prozesse ablaufen. Im Gegensatz dazu werden aus der Massenbilanz (Kap. 5.3) mittlere Transportzeiten aus der Troposphäre in die freie LMS von einigen Wochen bis zu mehreren Monaten abgeleitet. Außerdem konnte nachgewiesen werden, dass der troposphärische Eintrag in der freien LMS fast ausschließlich auf quasihorizontale isentrope Einmischung aus den Tropen über die Transportbarriere des Subtropenjets zurückzuführen ist. Nur im Sommer und Herbst konnte auch oberhalb der Übergangsschicht für einzelne Messungen ein Einfluss aus der extratropischen Troposphäre beobachtet werden. Die in dieser Arbeit untersuchten Tracerverteilungen und -korrelationen (Kap. 4) und die Verteilung des mittleren Alters (Kap.5.2) in der LMS zeigen einen Jahresgang mit einem maximalen troposphärischen Einfluss im Oktober und einem maximalen stratosphärischen Einfluss im April. Diese saisonale Charakteristik in der freien LMS kann durch die saisonalen Änderungen des Verhältnisses von Abwärtstransport aus der Overworld und quasihorizontalem Transport aus den Tropen und durch die mit den jeweiligen Transportprozessen assoziierte mittlere Transportzeiten erklärt werden, die aus Massenbilanzrechnungen bestimmt wurden. Es wird gezeigt, dass der überwiegende Eintrag von troposphärischer Luft in die LMS im Sommer und Herbst stattfindet, wobei im Mittel die kürzesten mittleren Transitzeiten (unter 0.3 Jahre) für den August und die längsten Transitzeiten (über 0.6 Jahre) für den Mai berechnet werden. Aus den Ergebnissen wird gefolgert, dass ein ausgeprägter isentroper Austauschprozess über den Subtropenjet im Sommer bis in den Herbst hinein der dominierende troposphärische Einfluss in der LMS bis in den Mai ist. Der Vergleich zwischen SPURT und anderen in der UT/LMS im Zeitraum von 1992 bis 1998 durchgeführten Messkampagnen zeigt einen systematischen Unterschied in den N2O/O3-Korrelationen. Die Zunahme von O3 relativ zu N2O in der LMS ist um etwa 6.5 ppb O3 pro 1 ppb N2O bzw. etwa 40% größer als die Zunahme bei jahreszeitlich vergleichbaren früheren Kampagnen. Durch eine weitergehende Analyse der Messungen, z.B. durch den Vergleich der N2O-Verteilungen in der LMS bei verschiedenen Messkampagnen, und zusätzlichen Informationen aus Satelliten- und Ballonmessungen wird abgeleitet, dass diese Änderung der N2O/O3-Korrelationen im Wesentlichen auf einen im Zeitraum von SPURT stärkeren quasihorizontalen Transport aus den Tropen in die Extratropen im Bereich des so genannten „tropical controlled transition layer“ [Rosenlof et al., 1997] zwischen 16-21 km (bzw. Θ ≈ 380-450 K) zurückzuführen ist. In Kooperation mit B. Bregman wurden mit dem Chemie-Transport-Modell TM5 des KNMI die Verteilungen von SF6 und CO2 in der Troposphäre und Stratosphäre, unter den Zielsetzungen Evaluation des Modelltransports und Erweiterung des Datensatzes von SPURT auf globalen Maßstab, für den Zeitraum 1.1.2000 bis 31.12.2002 modelliert. Dabei konnte gezeigt werden, dass bei Modellstudien zur Evaluation des Transports mit Hilfe von Alterstracern nicht nur troposphärisch monoton steigende Tracer wie SF6 sondern auch saisonal variable Tracer wie CO2 verwendet werden müssen. Bei dem Vergleich der Modellergebnisse des TM5 mit ER2- und SPURTMessungen zeigt sich, dass das Modell zum jetzigen Zeitpunkt in der Lage ist, das mittlere Alter in der unteren Stratosphäre und die SF6- und CO2-Verteilungen in der LMS qualitativ richtig wiederzugeben. Das mittlere Alter in der unteren Stratosphäre wird um etwa 0.5 bis 1 Jahr in den Tropen über- und in den Extratropen unterschätzt. Die vertikalen Gradienten im Modell für SF6 und CO2 in der LMS sind, insbesondere im Winter und Frühjahr, zu gering. Die Amplitude des CO2-Jahresganges in der oberen Troposphäre und in der LMS wird durch das Modell unterschätzt, während der saisonale Verlauf des Jahresganges richtig wiedergegeben wird. Im Moment wird vermutet, dass eine zu starke isentrope Mischung zwischen Tropen und Extratropen und/oder ein zu geringer Aufwärtstransport in der extratropischen Troposphäre im Sommer und Herbst die Ursachen für die beobachteten Abweichungen zwischen Modell und Messung sind.
- On the observation of mesospheric air inside the arctic stratospheric polar vortex in early 2003 (2005)
- During several balloon flights inside the Arctic polar vortex in early 2003, unusual trace gas distributions were observed, which indicate a strong influence of mesospheric air in the stratosphere. The tuneable diode laser (TDL) instrument SPIRALE (Spectroscopie InFrarouge par Absorption de Lasers Embarqués) measured unusually high CO values (up to 600 ppb) on 27 January at about 30 km altitude. The cryosampler BONBON sampled air masses with very high molecular Hydrogen, extremely low SF6 and enhanced CO values on 6 March at about 25 km altitude. Finally, the MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) Fourier Transform Infra-Red (FTIR) spectrometer showed NOy values which are significantly higher than NOy* (the NOy derived from a correlation between N2O and NOy under undisturbed conditions), on 21 and 22 March in a layer centred at 22 km altitude. Thus, the mesospheric air seems to have been present in a layer descending from about 30 km in late January to 25 km altitude in early March and about 22 km altitude on 20 March. We present corroborating evidence from a model study using the KASIMA (KArlsruhe Simulation model of the Middle Atmosphere) model that also shows a layer of mesospheric air, which descended into the stratosphere in November and early December 2002, before the minor warming which occurred in late December 2002 lead to a descent of upper stratospheric air, cutting of a layer in which mesospheric air is present. This layer then descended inside the vortex over the course of the winter. The same feature is found in trajectory calculations, based on a large number of trajectories started in the vicinity of the observations on 6 March. Based on the difference between the mean age derived from SF6 (which has an irreversible mesospheric loss) and from CO2 (whose mesospheric loss is much smaller and reversible) we estimate that the fraction of mesospheric air in the layer observed on 6 March, must have been somewhere between 35% and 100%.
- Corrigendum to "Fractional release factors of long-lived halogenated organic compounds in the tropical stratosphere" published in Atmos. Chem. Phys., 10, 1093–1103, 2010 (2010)
- We have noted a computational error in the calculation of the averaged Fractional Release Factors (FRFs) relative to the averaged FRF of CFCl3 (CFC-11). ...
- Impact of the Asian monsoon on the extratropical lower stratosphere: trace gas observations during TACTS over Europe 2012 (2016)
- The transport of air masses originating from the Asian monsoon anticyclone into the extratropical upper troposphere and lower stratosphere (Ex-UTLS) above potential temperatures Θ = 380 K was identified during the HALO aircraft mission TACTS in August and September 2012. In situ measurements of CO, O3 and N2O during TACTS flight 2 on 30 August 2012 show the irreversible mixing of aged stratospheric air masses with younger (recently transported from the troposphere) ones within the Ex-UTLS. Backward trajectories calculated with the trajectory module of CLaMS indicate that these tropospherically affected air masses originate from the Asian monsoon anticyclone. These air masses are subsequently transported above potential temperatures Θ = 380 K from the monsoon circulation region into the Ex-UTLS, where they subsequently mix with stratospheric air masses. The overall trace gas distribution measured during TACTS shows that this transport pathway had affected the chemical composition of the Ex-UTLS during boreal summer and autumn 2012. This leads to an intensification of the tropospheric influence on the extratropical lower stratosphere with PV > 8 pvu within 3 weeks during the TACTS mission. During the same time period a weakening of the tropospheric influence on the lowermost stratosphere (LMS) is determined. The study shows that the transport of air masses originating from the Asian summer monsoon region within the lower stratosphere affects the change in the chemical composition of the Ex-UTLS over Europe and thus contributes to the flushing of the LMS during summer 2012.
- Residual circulation trajectories and transit times into the extratropical lowermost stratosphere (2010)
- Transport into the extratropical lowermost stratosphere (LMS) can be divided into a slow part (time-scale of several months to years) associated with the global-scale stratospheric residual circulation and a fast part (time-scale of days to a few months) associated with (mostly quasi-horizontal) mixing (i.e. two-way irreversible transport, including stratosphere-troposphere exchange). The stratospheric residual circulation can be considered to consist of two branches: a deep branch more strongly associated with planetary waves breaking in the middle to upper stratosphere, and a shallow branch more strongly associated with synoptic-scale waves breaking in the subtropical lower stratosphere. In this study the contribution due to the stratospheric residual circulation alone to transport into the LMS is quantified using residual circulation trajectories, i.e. trajectories driven by the (time-dependent) residual mean meridional and vertical velocities. This contribution represents the advective part of the overall transport into the LMS and can be viewed as providing a background onto which the effect of mixing has to be added. Residual mean velocities are obtained from a comprehensive chemistry-climate model as well as from reanalysis data. Transit times of air traveling from the tropical tropopause to the LMS along the residual circulation streamfunction are evaluated and compared to recent mean age of air estimates. A clear time-scale separation with much smaller transit times into the mid-latitudinal LMS than into polar LMS is found that is indicative of a clear separation of the shallow from the deep branch of the residual circulation. This separation between the shallow and the deep circulation branch is further manifested in a clear distinction in the aspect ratio of the vertical to meridional extent of the trajectories as well as the integrated mass flux along the residual circulation trajectories. The residual transit time distribution reproduces qualitatively the observed seasonal cycle of youngest air in the extratropical LMS in fall and oldest air in spring.
- Highly resolved observations of trace gases in the lowermost stratosphere and upper troposphere from the Spurt project: an overview (2006)
- During SPURT (Spurenstofftransport in der Tropopausenregion, trace gas transport in the tropopause region) we performed measurements of a wide range of trace gases with different lifetimes and sink/source characteristics in the northern hemispheric upper troposphere (UT) and lowermost stratosphere (LMS). A large number of in-situ instruments were deployed on board a Learjet 35A, flying at altitudes up to 13.7 km, at times reaching to nearly 380 K potential temperature. Eight measurement campaigns (consisting of a total of 36 flights), distributed over all seasons and typically covering latitudes between 35° N and 75° N in the European longitude sector (10° W–20° E), were performed. Here we present an overview of the project, describing the instrumentation, the encountered meteorological situations during the campaigns and the data set available from SPURT. Measurements were obtained for N2O, CH4, CO, CO2, CFC12, H2, SF6, NO, NOy, O3 and H2O. We illustrate the strength of this new data set by showing mean distributions of the mixing ratios of selected trace gases, using a potential temperature – equivalent latitude coordinate system. The observations reveal that the LMS is most stratospheric in character during spring, with the highest mixing ratios of O3 and NOy and the lowest mixing ratios of N2O and SF6. The lowest mixing ratios of NOy and O3 are observed during autumn, together with the highest mixing ratios of N2O and SF6 indicating a strong tropospheric influence. For H2O, however, the maximum concentrations in the LMS are found during summer, suggesting unique (temperature- and convection-controlled) conditions for this molecule during transport across the tropopause. The SPURT data set is presently the most accurate and complete data set for many trace species in the LMS, and its main value is the simultaneous measurement of a suite of trace gases having different lifetimes and physical-chemical histories. It is thus very well suited for studies of atmospheric transport, for model validation, and for investigations of seasonal changes in the UT/LMS, as demonstrated in accompanying and elsewhere published studies.
- Observation of mesospheric air inside the arctic stratospheric polar vortex in early 2003 (2006)
- During several balloon flights inside the Arctic polar vortex in early 2003, unusual trace gas distributions were observed, which indicate a strong influence of mesospheric air in the stratosphere. The tuneable diode laser (TDL) instrument SPIRALE (Spectroscopie InFrarouge par Absorption de Lasers Embarqués) measured unusually high CO values (up to 600 ppb) on 27 January at about 30 km altitude. The cryosampler BONBON sampled air masses with very high molecular Hydrogen, extremely low SF6 and enhanced CO values on 6 March at about 25 km altitude. Finally, the MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) Fourier Transform Infra-Red (FTIR) spectrometer showed NOy values which are significantly higher than NOy* (the NOy derived from a correlation between N2O and NOy under undisturbed conditions), on 21 and 22 March in a layer centred at 22 km altitude. Thus, the mesospheric air seems to have been present in a layer descending from about 30 km in late January to 25 km altitude in early March and about 22 km altitude on 20 March. We present corroborating evidence from a model study using the KASIMA (KArlsruhe Simulation model of the Middle Atmosphere) model that also shows a layer of mesospheric air, which descended into the stratosphere in November and early December 2002, before the minor warming which occurred in late December 2002 lead to a descent of upper stratospheric air, cutting of a layer in which mesospheric air is present. This layer then descended inside the vortex over the course of the winter. The same feature is found in trajectory calculations, based on a large number of trajectories started in the vicinity of the observations on 6 March. Based on the difference between the mean age derived from SF6 (which has an irreversible mesospheric loss) and from CO2 (whose mesospheric loss is much smaller and reversible) we estimate that the fraction of mesospheric air in the layer observed on 6 March, must have been somewhere between 35% and 100%.
- Observation-based assessment of stratospheric fractional release, lifetimes, and ozone depletion potentials of ten important source gases (2013)
- Estimates of the recovery time of stratospheric ozone heavily rely on the exact knowledge of the processes that lead to the decomposition of the relevant halogenated source gases. Crucial parameters in this context are fractional release factors (FRFs) as well as stratospheric lifetimes and ozone depletion potentials (ODPs). We here present data from the analysis of air samples collected between 2009 and 2011 on board research aircraft flying in the mid- and high-latitude stratosphere and infer the above-mentioned parameters for ten major source gases: CFCl3 (CFC-11), CF2Cl2 (CFC-12), CF2ClCFCl2 (CFC-113), CCl4 (carbon tetrachloride), CH3CCl3 (methyl chloroform), CHF2Cl (HCFC-22), CH3CFCl2 (HCFC-141b), CH3CF2Cl (HCFC-142b), CF2ClBr (H-1211), and CF3Br (H-1301). The inferred correlations of their FRFs with mean ages of air reveal less decomposition as compared to previous studies for most compounds. When using the calculated set of FRFs to infer equivalent stratospheric chlorine, we find a reduction of more than 20% as compared to the values inferred in the most recent Scientific Assessment of Ozone Depletion by the World Meteorological Organisation (WMO, 2011). We also note that FRFs and their correlations with mean age are not generally time-independent as often assumed. The stratospheric lifetimes were calculated relative to that of CFC-11. Within our uncertainties the ratios between stratospheric lifetimes inferred here agree with the values in recent WMO reports except for CFC-11, CFC-12 and CH3CCl3. Finally, we calculate lower ODPs than recommended by WMO for six out of ten compounds, with changes most pronounced for the three HCFCs. Collectively these newly calculated values may have important implications for the severity and recovery time of stratospheric ozone loss.
- Mean age of stratospheric air derived from AirCore observations (2017)
- Mean age of stratospheric air can be derived from observations of sufficiently long lived trace gases with approximately linear trends in the troposphere. Mean age can serve as a tracer to investigate stratospheric transport and long term changes in the strength of the overturning Brewer-Dobson circulation of the stratosphere. For this purpose, a low-cost method is required in order to allow for regular observations up to altitudes of about 30 km. Despite the desired low costs, high precision and accuracy are required in order to allow determination of mean age. We present balloon borne AirCore observations from two mid latitude sites: Timmins in Ontario/Canada and Lindenberg in Germany. During the Timmins campaign five AirCores sampled air in parallel from a large stratospheric balloon and were analysed for CO2, CH4 and partly CO. We show that there is good agreement between the different AirCores (better than 0.1 %) especially when vertical gradients are small. The measurements from Lindenberg were performed using small low-cost balloons and yielded very comparable results. We have used the observations to extend our long term data set of mean age observations at Northern Hemi-sphere mid latitudes. The time series now covers more than 40 years and shows a small, statis-tically not significant positive trend of 0.15 ± 0.18 years/decade. This trend is slightly smaller than the previous estimate of 0.24 ± 0.22 years/decade which was based on observations up to the year 2006. These observations are still in contrast to strong negative trends of mean age as derived from some model calculations.
