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Small-scale thermal upwellings under the northern East African Rift from S travel time tomography
(2016)
There is a long-standing debate over how many and what types of plumes underlie the East African Rift and whether they do or do not drive its extension and consequent magmatism and seismicity. Here we present a new tomographic study of relative teleseismic S and SKS residuals that expands the resolution from previous regional studies below the northern East African Rift to image structure from the surface to the base of the transition zone. The images reveal two low-velocity clusters, below Afar and west of the Main Ethiopian Rift, that extend throughout the upper mantle and comprise several smaller-scale (about 100 km diameter), low-velocity features. These structures support those of our recent P tomographic study below the region. The relative magnitude of S to P residuals is around 3.5, which is consistent with a predominantly thermal nature of the anomalies. The S and P velocity anomalies in the low-velocity clusters can be explained by similar excess temperatures in the range of 100–200°C, consistent with temperatures inferred from other seismic, geochemical, and petrological studies. Somewhat stronger VS anomalies below Afar than west of the Main Ethiopian Rift may include an expression of volatiles and/or melt in this region. These results, together with a comparison with previous larger-scale tomographic models, indicate that these structures are likely small-scale upwellings with mild excess temperatures, rising from a regional thermal boundary layer at the base of the upper mantle.
The Fire Modeling Intercomparison Project (FireMIP), phase 1: experimental and analytical protocols
(2016)
The important role of fire in regulating vegetation community composition and contributions to emissions of greenhouse gases and aerosols make it a critical component of dynamic global vegetation models and Earth system models. Over two decades of development, a wide variety of model structures and mechanisms have been designed and incorporated into global fire models, which have been linked to different vegetation models. However, there has not yet been a systematic examination of how these different strategies contribute to model performance. Here we describe the structure of the first phase of the Fire Model Intercomparison Project (FireMIP), which for the first time seeks to systematically compare a number of models. By combining a standardized set of input data and model experiments with a rigorous comparison of model outputs to each other and to observations, we will improve the understanding of what drives vegetation fire, how it can best be simulated, and what new or improved observational data could allow better constraints on model behavior. Here we introduce the fire models used in the first phase of FireMIP, the simulation protocols applied, and the benchmarking system used to evaluate the models. The works published in this journal are distributed under the Creative Commons Attribution 3.0 License. This license does not affect the Crown copy-right work, which is re-usable under the Open Government Licence (OGL). The Creative Commons Attribution 3.0 License and the OGL are interoperable and do not conflict with, reduce, or limit each other.
The important role of fire in regulating vegetation community composition and contributions to emissions of greenhouse gases and aerosols make it a critical component of dynamic global vegetation models and Earth system models. Over 2 decades of development, a wide variety of model structures and mechanisms have been designed and incorporated into global fire models, which have been linked to different vegetation models. However, there has not yet been a systematic examination of how these different strategies contribute to model performance. Here we describe the structure of the first phase of the Fire Model Intercomparison Project (FireMIP), which for the first time seeks to systematically compare a number of models. By combining a standardized set of input data and model experiments with a rigorous comparison of model outputs to each other and to observations, we will improve the understanding of what drives vegetation fire, how it can best be simulated, and what new or improved observational data could allow better constraints on model behavior. In this paper, we introduce the fire models used in the first phase of FireMIP, the simulation protocols applied, and the benchmarking system used to evaluate the models. We have also created supplementary tables that describe, in thorough mathematical detail, the structure of each model.
In this study, we aim to reconstruct a relevant and new database of monthly zonal mean distribution of carbon dioxide (CO2) at global scale extending from the upper-troposphere (UT) to stratosphere (S). This product can be used for model and satellite validation in the UT/S, as a prior for inversion modelling and mainly to analyse a plausible feature of the stratospherictropospheric exchange as well as the stratospheric circulation and its variability. To do so, we investigate the ability of a Lagrangian trajectory model guided by ERA-Interim reanalysis to construct the CO2 abundance in the UT/S. From 10 year backward trajectories and tropospheric observations of CO2, we reconstruct upper-tropospheric and stratospheric CO2 over the period 2000–2010. The inter-comparisons of the reconstructed CO2 with mid-latitude vertical profiles measured by balloon samples as well as quasi-horizontal air samples from ER-2 aircraft during SOLVE and CONTRAIL campaigns exhibit a remarkable agreement. That demonstrates the potential of Lagrangian model to reconstruct CO2 in the UT/S. The zonal mean distribution exhibits relatively large CO2 in the tropical stratosphere due to the seasonal variation of the tropical upwelling of Brewer-Dobson circulation. During winter and spring, the tropical pipe is relatively isolated but is less confined during summer and autumn so that high CO2 values are more readily transported out of the tropics to the mid- and high latitude stratosphere. The shape of the vertical profiles suggests that relatively high CO2 above 20 km altitude mainly enter the stratosphere through tropical upwelling. CO2 mixing ratio is relatively low in the polar and tropical regions above 25 km. On average the CO2 mixing ratio decreases with altitude by 6-8 ppmv from the UT to stratosphere (e.g. up to 35 km) and is nearly constant with altitude.
In this study, we construct a new monthly zonal mean carbon dioxide (CO2) distribution from the upper troposphere to the stratosphere over the 2000–2010 time period. This reconstructed CO2 product is based on a Lagrangian backward trajectory model driven by ERA-Interim reanalysis meteorology and tropospheric CO2 measurements. Comparisons of our CO2 product to extratropical in situ measurements from aircraft transects and balloon profiles show remarkably good agreement. The main features of the CO2 distribution include (1) relatively large mixing ratios in the tropical stratosphere; (2) seasonal variability in the extratropics, with relatively high mixing ratios in the summer and autumn hemisphere in the 15–20 km altitude layer; and (3) decreasing mixing ratios with increasing altitude from the upper troposphere to the middle stratosphere ( ∼ 35 km). These features are consistent with expected variability due to the transport of long-lived trace gases by the stratospheric Brewer–Dobson circulation. The method used here to construct this CO2 product is unique from other modelling efforts and should be useful for model and satellite validation in the upper troposphere and stratosphere as a prior for inversion modelling and to analyse features of stratosphere–troposphere exchange as well as the stratospheric circulation and its variability.
The fractional release factor (FRF) gives information on the amount of a halocarbon that is released at some point in the stratosphere from its source form to the inorganic form, which can harm the ozone layer through catalytic reactions. The quantity is of major importance because it directly affects the calculation of the Ozone Depletion Potential (ODP). To apply FRF in this context, steady-state values are needed, thus representing a molecular property for a given atmospheric situation. In particular, these values should be independent of the tropospheric trends of the respective halogenated trace gases.
We analyzed the temporal evolution of FRF from ECHAM/MESSy Atmospheric Chemistry (EMAC) model simulations for several halocarbons and nitrous oxide between 1965–2011 on different mean age levels and found that the current formulation of FRF yields highly time-dependent values. We show that this is caused by the way that the tropospheric trend is handled in the current calculation method of FRF.
Taking into account chemical loss in the calculation of stratospheric mixing ratios reduces the time-dependence in correlations of different tracers. Therefore we implemented a loss term in the formulation of FRF and applied the parameterization of a "mean arrival time" to our data set.
We find that the time-dependence in FRF can almost be compensated by applying a new trend correction in the calculation of FRF. We suggest that this new method should be used to calculate time-independent FRF, which can then be used e.g. for the calculation of ODP
The fractional release factor (FRF) gives information on the amount of a halocarbon that is released at some point into the stratosphere from its source form to the inorganic form, which can harm the ozone layer through catalytic reactions. The quantity is of major importance because it directly affects the calculation of the ozone depletion potential (ODP). In this context time-independent values are needed which, in particular, should be independent of the trends in the tropospheric mixing ratios (tropospheric trends) of the respective halogenated trace gases. For a given atmospheric situation, such FRF values would represent a molecular property.
We analysed the temporal evolution of FRF from ECHAM/MESSy Atmospheric Chemistry (EMAC) model simulations for several halocarbons and nitrous oxide between 1965 and 2011 on different mean age levels and found that the widely used formulation of FRF yields highly time-dependent values. We show that this is caused by the way that the tropospheric trend is handled in the widely used calculation method of FRF.
Taking into account chemical loss in the calculation of stratospheric mixing ratios reduces the time dependence in FRFs. Therefore we implemented a loss term in the formulation of the FRF and applied the parameterization of a mean arrival time to our data set.
We find that the time dependence in the FRF can almost be compensated for by applying a new trend correction in the calculation of the FRF. We suggest that this new method should be used to calculate time-independent FRFs, which can then be used e.g. for the calculation of ODP.
Medium range hydrological forecasts in mesoscale catchments are only possible with the use of hydrological models driven by meteorological forecasts, which in particular contribute quantitative precipitation forecasts (QPF). QPFs are accompanied by large uncertainties, especially for longer lead times, which are propagated within the hydrometeorological model system. To deal with this limitation of predictability, a probabilistic forecasting system is tested, which is based on a hydrological-meteorological ensemble prediction system. The meteorological component of the system is the operational limited-area ensemble prediction system COSMO-LEPS that downscales the global ECMWF ensemble to a horizontal resolution of 10 km, while the hydrological component is based on the semi-distributed hydrological model PREVAH with a spatial resolution of 500 m.
Earlier studies have mostly addressed the potential benefits of hydrometeorological ensemble systems in short case studies. Here we present an analysis of hydrological ensemble hindcasts for two years (2005 and 2006). It is shown that the ensemble covers the uncertainty during different weather situations with an appropriate spread-skill relationship. The ensemble also shows advantages over a corresponding deterministic forecast, even under consideration of an artificial spread.
Volatile organic compounds (VOCs) were analyzed in air and snow samples at the Jungfraujoch high alpine research station in Switzerland as part of CLACE 5 (CLoud and Aerosol Characterization Experiment) during February/March 2006. The fluxes of individual compounds in ambient air were calculated from gas phase concentrations and wind speed. The highest flux values were observed for the aromatic hydrocarbons benzene (14.3 µg m−2s−1), 1,3,5-trimethylbenzene (5.27 µg m−2s−1), toluene (4.40 µg m−2s−1), and the aliphatic hydrocarbons i-butane (7.87 µg m−2s−1), i-pentane (3.61 µg m−2s−1) and n-butane (3.23 µg m−2s−1). The fluxes were used to calculate the efficiency of removal of VOCs by snow, and the effect of temperature on removal efficiency. The removal efficiency was calculated at – 24◦C (−13.7◦C) and ranged from 37% (35%) for o-xylene to 93% (63%) for i-pentane. The distribution coefficients of VOCs between the air and snow phases were derived from published poly-parameter linear free energy relationship (pp-LFER) data, and compared with distribution coef- ficients obtained from the simultaneous measurements of VOC concentrations in air and snow at Jungfraujoch. The coefficients calculated from pp-LFER exceeded those values measured in the present study, which indicates more efficient snow scavenging of the VOCs investigated than suggested by theoretical predictions.
Quantification of spatially and temporally resolved water flows and water storage variations for all land areas of the globe is required to assess water resources, water scarcity and flood hazards, and to understand the Earth system. This quantification is done with the help of global hydrological models (GHMs). What are the challenges and prospects in the development and application of GHMs? Seven important challenges are presented. (1) Data scarcity makes quantification of human water use difficult even though significant progress has been achieved in the last decade. (2) Uncertainty of meteorological input data strongly affects model outputs. (3) The reaction of vegetation to changing climate and CO2 concentrations is uncertain and not taken into account in most GHMs that serve to estimate climate change impacts. (4) Reasons for discrepant responses of GHMs to changing climate have yet to be identified. (5) More accurate estimates of monthly time series of water availability and use are needed to provide good indicators of water scarcity. (6) Integration of gradient-based groundwater modelling into GHMs is necessary for a better simulation of groundwater–surface water interactions and capillary rise. (7) Detection and attribution of human interference with freshwater systems by using GHMs are constrained by data of insufficient quality but also GHM uncertainty itself. Regarding prospects for progress, we propose to decrease the uncertainty of GHM output by making better use of in situ and remotely sensed observations of output variables such as river discharge or total water storage variations by multi-criteria validation, calibration or data assimilation. Finally, we present an initiative that works towards the vision of hyperresolution global hydrological modelling where GHM outputs would be provided at a 1-km resolution with reasonable accuracy.
Samples of freshly fallen snow were collected at the high alpine research station Jungfraujoch (Switzerland) in February and March 2006 and 2007, during the Cloud and Aerosol Characterization Experiments (CLACE) 5 and 6. In this study a new technique has been developed and demonstrated for the measurement of organic acids in fresh snow. The melted snow samples were subjected to solid phase extraction and resulting solution analysed for organic acids by HPLC-MS-TOF using negative electrospray ionization. A series of linear dicarboxylic acids from C5 to C13 and phthalic acid, were identified and quantified. In several samples the biogenic acid pinonic acid was also observed. In fresh snow the median concentration of the most abundant acid, adipic acid, was 0.69 µg L−1 in 2006 and 0.70 µg L−1 in 2007. Glutaric acid was the second most abundant dicarboxylic acid found with median values of 0.46 µg L−1 in 2006 and 0.61 µg L−1 in 2007, while the aromatic acid phthalic acid showed a median concentration of 0.34 µg L−1 in 2006 and 0.45 µg L−1 in 2007. The concentrations in the samples from various snowfall events varied significantly, and were found to be dependent on the back trajectory of the air mass arriving at Jungfraujoch. Air masses of marine origin showed the lowest concentrations of acids whereas the highest concentrations were measured when the air mass was strongly influenced by boundary layer air.
This PhD thesis has been carried out within an interdisciplinary cooperational project between the Deutsches Bergbau-Museum Bochum and the Goethe-Universität Frankfurt, which is dedicated to ancient Pb-Ag mining and metal production in the hinterland of the municipium Ulpiana in central Kosovo. Geochemical analysis (OM, XRD, EMP, MC-ICP-MS) of ores, metallurgical (by-) products and metal artefacts allowed to reconstruct the local chaîne opératoire and to decipher significant chronological differences between presumably Roman/late antique and medieval/early modern metallurgical processing. Pb isotope provenance studies documented the relevance of local metal production within the Roman Empire and confirmed the actual existence of a Metalla Dardanica district, which until now solely has been suspected on basis of epigraphy.
The predominant abundance of the by-products matte (Cu, Pb, Fe and Zn sulphides) and speiss (ferrous speiss: Fe-As compounds; base metal speiss: ~(Cu,Ni,Fe,Ag )x(Sb,Sn,As )y ) at smelting sites with a preliminary Roman/late antique dating points to treatment of complex polymetallic ore. Pb isotope analysis demonstrated that the mining district of Shashkoc-Janjevo (partially) supplied six of the ten investigated metallurgical sites. In this mineralisation, parageneses with elevated Cu, As and Sb abundances comprise significant proportions of particularly tennantite-tetrahedrite minerals, chalcopyrite, arsenopyrite and were generated during the early and main stages of ore formation. Later precipitated ore in contrast is marked by a significantly less versatile mineralogy and consists almost exclusively of galena, sphalerite and pyrite/marcasite. Besides increased Cu, As and Sb contents, ore from the main formation stage also exhibits generally higher Ag abundances, which are mainly hosted by fahlore and locally abundant secondary Cu sulphides (chalcocite, digenite and covellite) and oxidised phases (e.g. malachite, azurite). The higher precious metal grades of this ore type, whose geochemical signature (i.e. higher proportions of Cu, As and Sb) is mirrored by the abundance of the metallurgical by-products matte and speiss (almost exclusively found at potentially Roman/late antique smelting sites; see above), presumably were a pivotal factor leading to its preferential exploitation in earlier times. Matte and base metal-rich speiss contain notable amounts of Ag, which are mainly present in Cu-(Fe) sulphides and particularly antimonides ((Cu,Ni)2Sb, Ag3Sb), respectively. While the speiss compounds due to their close association with Pb bullion presumably were cupelled automatically, the metallurgical treatment of matte could not have been proven unambiguously, but overall certainly is highly likely.
The beneficiated ore (i.e. crushed and sorted, potentially also treated by more lavish techniques such as grinding, sieving or wet-mechanical methods) possibly was partially roasted and subsequently together with fluxes and charcoal submitted to the furnaces. The working temperatures approximately ranged between 1100 and 1400 °C. Slags from all presumably Roman/late antique dated and few of their potentially medieval/early modern analogues were produced from smelting of (partially roasted) ore with charcoal and added siliceous material, thus resulting in fayalite-dominant phase assemblages or rarely observed glassy parageneses. Even though several subtypes of fayalite slags have been established on basis of the abundance of Fe-rich oxide phases (i.e. spinel ss and wüstite), late clinopyroxene and the general solidification sequence of the slags, the process conditions (i.e. temperature, fO2, added fluxing agents) must have been widely similar; chemical variations could be explained by varying degrees of interaction of the slag melt with charcoal ash and furnace material. The other investigated metallurgical remains indicate employment of a calcareous flux, which led to formation of Ca-rich olivine-, olivine+clinopyroxene-, clinopyroxene- or melilite-type slags. These types as well as glassy slags were generated at more oxidising conditions outside the fayalite stability field (FMQ buffer equilibrium, cf. Lindsley, 1976) than their olivine-dominant analogues. Conclusions on the furnace construction could be drawn on basis of the typology of the slags, which mostly were tapped into a basin located outside the furnace, but partially (at two presumably medieval/early modern sites) also accumulated in a reservoir within the smelter.
Lead artefacts excavated in Ulpiana could be isotopically related to ores from mineralisations in its vicinity and demonstrate that the resources were at least utilised for local metal production. However, also ship wreck cargo from Israel - including several lead ingots with the inscription 'MET DARD' (Raban, 1999) - and late antique lead-glazed pottery from Serbia and Romania (Walton & Tite, 2010) could be related to a possible Kosovarian/Serbian provenance of the raw material and thus indicate flourishing trade of metal from the Metalla Dardanica district within the Roman Empire.
References:
Lindsley, D. H. (1976). Experimental studies of oxide minerals. In D. Rumble, III (Hrsg.), Oxide minerals (61-88). Reviews in Mineralogy, Volume 3. Washington, DC: Mineralogical Society of America.
Raban, A. (1999). The lead ingots from the wreck site (area K8). Journal of Roman Archaeology, Supplementary Series, 35, 179-188.
Walton, M. S., & Tite, M. S. (2010). Production technology of Roman lead-glazed pottery and its continuance into late antiquity. Archaeometry, 52(5), 733-759.
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.
Ziel der Arbeit war es, die Flugzeitmassenspektrometrie als neue Analysemethode für die instrumentelle Analytik halogenierter Spurengase in der Luft zu etablieren. Die grundle-gende Motivation dafür ist, dass anthropogene Emissionen vieler Vertreter dieser Sub-stanzklasse einen negativen Einfluss auf die Umwelt zeigen: in der Atmosphäre agieren die Substanzen bzw. ihre Abbauprodukte als Katalysatoren für den stratosphärischen Ozonab-bau und verstärken den Strahlungsantrieb der Erde durch Absorption elektromagnetischer Strahlung im sogenannten atmosphärischen Fenster. Um diese Effekte und deren Auswir-kung quantifizieren zu können, ist es notwendig, Konzentrationen und Trends der Substan-zen in der Atmosphäre zu überwachen. Nur so können Gegenmaßnahmen wie Produktions-reglementierungen geplant und bewertet werden. In Kombination mit inverser Modellie-rung können zudem Rückschlüsse über tatsächlich emittierten Mengen gezogen werden. Dies stellt den Anspruch an die Analytik, sehr geringe Mengen dieser Gase sehr präzise quantifizieren zu können, um auch schwache Trends zu erkennen. Zudem muss die Analy-semethode die Möglichkeit zu bieten, mit der wachsenden Anzahl bekannter und zu über-wachender Substanzen Schritt zu halten. Besonders für letzteren Aspekt bietet die Flug-zeitmassenspektrometrie einen entscheidenden Vorteil gegenüber der „konventionellen“ Methode, der Quadrupolmassenspektrometrie: sie zeichnet das gesamten Massenspektrum auf ohne dadurch an Empfindlichkeit einzubüßen. Um das atmosphärische Mischungsver-hältnis von Substanzen im Bereich von pmol mol−1 bis fmol mol−1 bestimmen zu können, muss das Quadrupolmassenspektrometer im Single Ion Monitoring Modus betrieben wer-den – so wird zwar eine hohe Sensitivität erreicht, es wird aber auch nur die Intensität eines bestimmten Masse zu Ladungsverhältnisses (kurz: Masse) zu einem Zeitpunkt aufgezeich-net. Ein Flugzeitmassenspektrometer hingegen extrahiert Ionen mit einer Frequenz im Ki-loherzbereich und zeichnet für jede Extraktion das vollständige Flugzeitspektrum und da-mit Massenspektrum auf.
Aufgabe dieser Arbeit war es, ein Flugzeitmassenspektrometer mit vorgeschalteter Pro-benanreicherungseinheit sowie Gaschromatograph zur Trennung des Subtanzgemisches vor der Detektion aufzubauen und Werkzeuge zur Datenauswertung zu entwickeln. Um einen zukünftigen Feldeinsatz vorzubereiten, sollte der Aufbau möglichst kompakt, mobil und vollständig automatisiert sein. Anschließend sollte Empfindlichkeit, Präzision und dynami-scher Messbereich geprüft, optimiert und die Anwendbarkeit zur Analyse halogenierter Spurengase gezeigt werden. Die Ergebnisse aus der in der vorliegenden Arbeit präsentier-ten Geräteentwicklung finden sich in drei Publikationen wieder, welche in thematischer Reihenfolge die Probenanreicherung (Obersteiner et al., 2016b), den Vergleich von Quadrupol- und Flugzeitmassenspektrometrie (Hoker et al., 2015) sowie Eigenschaften und Anwendung des neuen Aufbaus (Obersteiner et al., 2016a) behandeln. Mit den genannten Aufsätzen ist die Arbeitsgruppe Engel weltweit die erste, welche hochpräzise Analytik ha-logenierter Spurengase routinemäßig mittels Flugzeitmassenspektrometrie durchführt. Der nächste Schritt ist der Übergang von der Laboranwendung zur Feldmessung, z.B. in Form von bodenbasierter in situ Analyse troposphärischer Luftmassen am Taunus Observatorium auf dem Kleinen Feldberg. Da es bisher keine Messstation für die hier beschriebene analy-tische Fragestellung in Deutschland gibt, könnte eine deutliche Verbesserung der Überwa-chung halogenierter Treibhausgase und ozonzerstörender Substanzen in Europa erzielt wer-den. Weiterhin wäre eine Flugzeugapplikation in Zukunft denkbar, welche neben der durch das Flugzeitmassenspektrometer abgedeckten Substanzbandbreite auch von dessen hoher möglicher Spektrenrate profitieren könnte. In Kombination mit Hochgeschwindigkeitsgas-chromatographie könnte eine bisher unerreichte Zeitauflösung der Beprobung der Atmo-sphäre mittels Gaschromatographie-Massenspektrometrie erzielt werden.
Aerosolteilchen agieren als Kondensationskeime für Wolkentröpfchen (engl. Cloud Condensation Nuclei, CCN) oder Eiskristalle und sind deswegen für die Wolken- und Niederschlagsbildung entscheidend. Sowohl die Aerosolpartikel als auch die Wolken können Sonnenlicht effizient streuen, wodurch ein kühlender Effekt auf das Klima ausgeübt wird. Einige der Teilchen, wie z. B. aufgewirbelter Staub oder Seesalz, werden direkt in die Atmosphäre injiziert; der größte Anteil der Teilchen und etwa die Hälfte der CCN werden allerdings durch die Kondensation gasförmiger Substanzen gebildet. Dieser Prozess wird als Nukleation oder Partikelneubildung (engl. New Particle Formation, NPF) bezeichnet. Trotz intensiver Forschung ist die NPF noch nicht vollständig verstanden, was an der Komplexität der chemischen Abläufe in der Atmosphäre und an der Schwierigkeit liegt, die relevanten Substanzen bei extrem geringen Mischungsverhältnissen (etwa ein Molekül oder Cluster per 1012 bis 1015 Moleküle) zu identifizieren und zu quantifizieren. Neben der Frage nach den bei der Nukleation beteiligten Substanzen ist außerdem noch unklar, ob Ionen-induzierte Nukleation ein wichtiger Prozess für das Klima ist. Das CLOUD-Projekt (Cosmics Leaving OUtdoor Droplets) am CERN soll diesen Fragen nachgehen, indem dort die Partikelbildung in einem Kammer-Experiment unter extrem gut kontrollierten Bedingungen simuliert wird. Die chemischen Systeme, die in dieser Schrift diskutiert werden, umfassen das binäre (H2SO4-H2O), das ternäre Ammoniak (H2SO4-H2O-NH3) und das ternäre Dimethylamin (H2SO4-H2O-(CH3)2NH)-System.
Einige der wesentlichen Ergebnisse von Experimenten an der CLOUD-Kammer werden diskutiert. Diese zeigen, dass das binäre und das ternäre Ammoniak System die atmosphärische Nukleation bei niedrigen Temperaturen erklären können, wohingegen das ternäre Dimethylamin System prinzipiell in der Lage ist, die hohen bodennahen Nukleationsraten bei atmosphärisch relevanten Schwefelsäure-Konzentrationen zu beschreiben. Des Weiteren werden zwei für Nukleationsstudien wesentliche Messmethoden vorgestellt. Das Chemical Ionization Mass Spectrometer (CIMS) wird zur Messung von gasförmiger Schwefelsäure verwendet, da H2SO4 vermutlich die wichtigste Substanz bei der atmosphärischen Nukleation ist. Das Chemical Ionization-Atmospheric Pressure interface-Time Of Flight (CI-APi-TOF) Massenspektrometer misst Schwefelsäure und neutrale Cluster. Beide Geräte wurden für den Einsatz bei CLOUD optimiert und instrumentelle Entwicklungen wurden in Bezug auf die Ionenquelle vorgenommen, die eine Korona-Entladung verwendet. Außerdem wurden eine Kalibrationseinheit zur Bereitstellung definierter Schwefelsäure-Konzentrationen entwickelt und das CI-APi-TOF aufgebaut. In Bezug auf das ternäre Dimethylamin System werden Nukleationsraten und die ersten Messungen von gro en nukleierenden neutralen Clustern präsentiert. Monomer- und Dimer-Konzentrationen der Schwefelsäure, die mit dem CIMS bei tiefen Temperaturen gemessen wurden, dienten der Ableitung der thermodynamischen Eigenschaften bei der Dimer-Bildung im binären und ternären Ammoniak System. Um möglichst exakte Nukleationsraten zu bestimmen, wurde eine neue Methode entwickelt, die es erlaubt, den Effekt der Selbst-Koagulation bei der Nukleation miteinzubeziehen.
Die zusammengefassten Studien tragen signifikant zum Verständnis der Partikelneubildung bei.
Desert dust is one of the most abundant ice nucleating particle types in the atmosphere. Traditionally, clay minerals were assumed to determine the ice nucleation ability of desert dust and constituted the focus of ice nucleation studies over several decades. Recently some feldspar species were identified to be ice active at much higher temperatures than clay minerals, redirecting studies to investigate the contribution of feldspar to ice nucleation on desert dust. However, so far no study has shown the atmospheric relevance of this mineral phase.
For this study four dust samples were collected after airborne transport in the troposphere from the Sahara to different locations (Crete, the Peloponnese, Canary Islands, and the Sinai Peninsula). Additionally, 11 dust samples were collected from the surface from nine of the biggest deserts worldwide. The samples were used to study the ice nucleation behavior specific to different desert dusts. Furthermore, we investigated how representative surface-collected dust is for the atmosphere by comparing to the ice nucleation activity of the airborne samples. We used the IMCA-ZINC setup to form droplets on single aerosol particles which were subsequently exposed to temperatures between 233 and 250 K. Dust particles were collected in parallel on filters for offline cold-stage ice nucleation experiments at 253–263 K. To help the interpretation of the ice nucleation experiments the mineralogical composition of the dusts was investigated. We find that a higher ice nucleation activity in a given sample at 253 K can be attributed to the K-feldspar content present in this sample, whereas at temperatures between 238 and 245 K it is attributed to the sum of feldspar and quartz content present. A high clay content, in contrast, is associated with lower ice nucleation activity. This confirms the importance of feldspar above 250 K and the role of quartz and feldspars determining the ice nucleation activities at lower temperatures as found by earlier studies for monomineral dusts. The airborne samples show on average a lower ice nucleation activity than the surface-collected ones. Furthermore, we find that under certain conditions milling can lead to a decrease in the ice nucleation ability of polymineral samples due to the different hardness and cleavage of individual mineral phases causing an increase of minerals with low ice nucleation ability in the atmospherically relevant size fraction. Comparison of our data set to an existing desert dust parameterization confirms its applicability for climate models. Our results suggest that for an improved prediction of the ice nucleation ability of desert dust in the atmosphere, the modeling of emission and atmospheric transport of the feldspar and quartz mineral phases would be key, while other minerals are only of minor importance.
Desert dust is one of the most abundant ice nucleating particle types in the atmosphere. Tra ditionally, clay minerals were assumed to determine the ice nucleation ability of desert dust and constituted the focus of ice nucleation studies. Only recently some feldspar species were identified to be ice-active at much higher temperatures than clay minerals, redirecting studies to investigate the contribution of feldspar to ice nucleation on desert dust. However, so far no study has shown the atmospheric relevance of this mineral phase.
For this study four dust samples were collected after airborne transport in the troposphere from the Sahara to different locations (Crete, the Peloponnese, Canary Islands and the Sinai Peninsula). Additionally, eleven dust samples were collected from the surface from nine of the biggest deserts worldwide. The samples were used to study the ice nucleation behavior specific to different desert dusts. Furthermore we investigated how representative ice nucleation on surface-collected dust is for that in the atmosphere by comparing to the ice nucleation activity of the airborne samples. We used the IMCA-ZINC set-up to form droplets on single aerosol particles which were subsequently exposed to temperatures between 233 - 250 K. Dust particles were collected in parallel on filters for offline cold stage ice nucleation experiments at 253 - 263 K. To help the interpretation of the results from the ice nucleation experiments the mineralogical composition of the dusts was investigated.We found that a higher ice nucleation activity in a given sample can be attributed at 253 K to the K-feldspar content present in this sample whereas at temperatures between 238 - 245 K it is attributed to the sum of feldspar and quartz content present. A high clay content on the other hand is associated with a lower ice nucleation activity of a sample. This confirms the importance of feldspar at T > 250 K and the role of quartz and feldspars determining the ice nucleation activities at lower T as found by earlier studies for monomineral dust surrogates. Furthermore, we find that milling may lead to a decrease in the ice nucleation ability of polymineral samples due to a change in mineralogical composition in the atmospherically relevant size fraction arising from the different hardness and cleavage of individual mineral phases. Comparison of our comprehensive data set to an existing desert dust parameterization confirms its applicability for climate models. Our results suggest that for an improved prediction of the ice nucleation ability of desert dust in the atmosphere, the modelling of emission and atmospheric transport of the feldspar and quartz mineral phases would be key while other minerals are only of minor importance.
In situ single particle analysis of ice particle residuals (IPRs) and out-of-cloud aerosol particles was conducted by means of laser ablation mass spectrometry during the intensive INUIT-JFJ/CLACE campaign at the high alpine research station Jungfraujoch (3580 m a.s.l.) in January–February 2013. During the 4-week campaign more than 70 000 out-of-cloud aerosol particles and 595 IPRs were analyzed covering a particle size diameter range from 100 nm to 3 µm. The IPRs were sampled during 273 h while the station was covered by mixed-phase clouds at ambient temperatures between −27 and −6 °C. The identification of particle types is based on laboratory studies of different types of biological, mineral and anthropogenic aerosol particles. The outcome of these laboratory studies was characteristic marker peaks for each investigated particle type. These marker peaks were applied to the field data. In the sampled IPRs we identified a larger number fraction of primary aerosol particles, like soil dust (13 ± 5 %) and minerals (11 ± 5 %), in comparison to out-of-cloud aerosol particles (2.4 ± 0.4 and 0.4 ± 0.1 %, respectively). Additionally, anthropogenic aerosol particles, such as particles from industrial emissions and lead-containing particles, were found to be more abundant in the IPRs than in the out-of-cloud aerosol. In the out-of-cloud aerosol we identified a large fraction of aged particles (31 ± 5 %), including organic material and secondary inorganics, whereas this particle type was much less abundant (2.7 ± 1.3 %) in the IPRs. In a selected subset of the data where a direct comparison between out-of-cloud aerosol particles and IPRs in air masses with similar origin was possible, a pronounced enhancement of biological particles was found in the IPRs.
In-situ single particle analysis of ice particle residuals (IPR) and out-of-cloud aerosol particles was conducted by means of laser ablation mass spectrometry during the intensive INUIT-JFJ/CLACE campaign at the high alpine research station Jungfraujoch (3580 m a.s.l.) in January/February 2013. During the four week campaign more than 70000 out-of-cloud aerosol particles and 595 IPR were analyzed covering a particle size diameter range from 100 nm to 3 μm. The IPR were sampled during 273 hours while the station was covered by mixed-phase clouds at ambient temperatures between -27 °C and -6 °C. The identification of particle types is based on laboratory studies of different types of biological, mineral and anthropogenic aerosol particles. As outcome instrument specific marker peaks for the different investigated particle types were obtained and applied to the field data. The results show that the sampled IPR contain a larger relative amount of natural, primary aerosol, like soil dust (13 %) and minerals (11 %), in comparison to out-of-cloud aerosol particles (2 % and <1 %, respectively). Additionally, anthropogenic aerosol particles, like particles from industrial emissions and lead-containing particles, were found to be more abundant in the IPR than in the out-of-cloud aerosol. The out of-cloud aerosol contained a large fraction of aged particles (30 %, including organic material and secondary inorganics), whereas this particle type was much less abundant (3 %) in the IPR. In a selected subset of the data where a direct comparison between out-of-cloud aerosol particles and IPR in air masses with similar origin was possible, a pronounced enhancement of biological particles was found in the IPR.
Size-resolved long-term measurements of atmospheric aerosol and cloud condensation nuclei (CCN) concentrations and hygroscopicity were conducted at the remote Amazon Tall Tower Observatory (ATTO) in the central Amazon Basin over a 1-year period and full seasonal cycle (March 2014–February 2015). The measurements provide a climatology of CCN properties characteristic of a remote central Amazonian rain forest site.
The CCN measurements were continuously cycled through 10 levels of supersaturation (S = 0.11 to 1.10 %) and span the aerosol particle size range from 20 to 245 nm. The mean critical diameters of CCN activation range from 43 nm at S = 1.10 % to 172 nm at S = 0.11 %. The particle hygroscopicity exhibits a pronounced size dependence with lower values for the Aitken mode (κAit = 0.14 ± 0.03), higher values for the accumulation mode (κAcc = 0.22 ± 0.05), and an overall mean value of κmean = 0.17 ± 0.06, consistent with high fractions of organic aerosol.
The hygroscopicity parameter, κ, exhibits remarkably little temporal variability: no pronounced diurnal cycles, only weak seasonal trends, and few short-term variations during long-range transport events. In contrast, the CCN number concentrations exhibit a pronounced seasonal cycle, tracking the pollution-related seasonality in total aerosol concentration. We find that the variability in the CCN concentrations in the central Amazon is mostly driven by aerosol particle number concentration and size distribution, while variations in aerosol hygroscopicity and chemical composition matter only during a few episodes.
For modeling purposes, we compare different approaches of predicting CCN number concentration and present a novel parametrization, which allows accurate CCN predictions based on a small set of input data.