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We developed a coupled regional climate system model based on the CCLM regional climate model. Within this model system, using OASIS3-MCT as a coupler, CCLM can be coupled to two land surface models (the Community Land Model (CLM) and VEG3D), the NEMO-MED12 regional ocean model for the Mediterranean Sea, two ocean models for the North and Baltic seas (NEMO-NORDIC and TRIMNP+CICE) and the MPI-ESM Earth system model.
We first present the different model components and the unified OASIS3-MCT interface which handles all couplings in a consistent way, minimising the model source code modifications and defining the physical and numerical aspects of the couplings. We also address specific coupling issues like the handling of different domains, multiple usage of the MCT library and exchange of 3-D fields.
We analyse and compare the computational performance of the different couplings based on real-case simulations over Europe. The usage of the LUCIA tool implemented in OASIS3-MCT enables the quantification of the contributions of the coupled components to the overall coupling cost. These individual contributions are (1) cost of the model(s) coupled, (2) direct cost of coupling including horizontal interpolation and communication between the components, (3) load imbalance, (4) cost of different usage of processors by CCLM in coupled and stand-alone mode and (5) residual cost including i.a. CCLM additional computations.
Finally a procedure for finding an optimum processor configuration for each of the couplings was developed considering the time to solution, computing cost and parallel efficiency of the simulation. The optimum configurations are presented for sequential, concurrent and mixed (sequential+concurrent) coupling layouts. The procedure applied can be regarded as independent of the specific coupling layout and coupling details.
We found that the direct cost of coupling, i.e. communications and horizontal interpolation, in OASIS3-MCT remains below 7 % of the CCLM stand-alone cost for all couplings investigated. This is in particular true for the exchange of 450 2-D fields between CCLM and MPI-ESM. We identified remaining limitations in the coupling strategies and discuss possible future improvements of the computational efficiency.
The formation of secondary particles in the atmosphere accounts for more than half of global cloud condensation nuclei. Experiments at the CERN CLOUD (Cosmics Leaving OUtdoor Droplets) chamber have underlined the importance of ions for new particle formation, but quantifying their effect in the atmosphere remains challenging. By using a novel instrument setup consisting of two nano-particle counters, one of them equipped with an ion filter, we were able to further investigate the ion-related mechanisms of new particle formation. In autumn 2015, we carried out experiments at CLOUD on four systems of different chemical compositions involving monoterpenes, sulfuric acid, nitrogen oxides, and ammonia. We measured the influence of ions on the nucleation rates under precisely controlled and atmospherically relevant conditions. Our results indicate that ions enhance the nucleation process when the charge is necessary to stabilize newly formed clusters, i.e. in conditions where neutral clusters are unstable. For charged clusters that were formed by ion-induced nucleation, we were able to measure, for the first time, their progressive neutralization due to recombination with oppositely charged ions. A large fraction of the clusters carried a charge at 1.2 nm diameter. However, depending on particle growth rates and ion concentrations, charged clusters were largely neutralized by ion–ion recombination before they grew to 2.2 nm. At this size, more than 90 % of particles were neutral. In other words, particles may originate from ion-induced nucleation, although they are neutral upon detection at diameters larger than 2.2 nm. Observations at Hyytiälä, Finland, showed lower ion concentrations and a lower contribution of ion-induced nucleation than measured at CLOUD under similar conditions. Although this can be partly explained by the observation that ion-induced fractions decrease towards lower ion concentrations, further investigations are needed to resolve the origin of the discrepancy.
The CLOUD (Cosmics Leaving OUtdoor Droplets) experiment at CERN is studying the nucleation and growth of aerosol particles under atmospheric conditions, and their activation into cloud droplets. A key feature of the CLOUD experiment is precise control of the experimental parameters. Temperature uniformity and stability in the chamber are important since many of the processes under study are sensitive to temperature and also to contaminants that can be released from the stainless steel walls by upward temperature fluctuations. The air enclosed within the 3 m CLOUD chamber is equipped with several arrays (strings) of high precision, fast-response thermometers to measure its temperature. Here we present a study of the air temperature uniformity inside the CLOUD chamber under various experimental conditions. Measurements were performed under calibration conditions and run conditions, which are distinguished by the flow rate of fresh air and trace gases entering the chamber: 20 l/min and up to 210 l/min, respectively. During steady-state calibration runs between −70 °C and +20 °C, the air temperature uniformity is better than +/−0.06 °C in the radial direction and +/−0.1 °C in the vertical direction. Larger non-uniformities are present during experimental runs, depending on the temperature control of the make-up air and trace gases (since some trace gases require elevated temperatures until injection into the chamber). The temperature stability is a few times 0.01 °C over periods of several hours during either calibration or steady-state run conditions. During rapid adiabatic expansions to activate cloud droplets and ice particles, the chamber walls are up to 10 °C warmer than the enclosed air. This results in larger non-uniformities while the air returns to its equilibrium temperature with time constant of about 200 s.
Evaluation of radiation components in a global freshwater model with station-based observations
(2016)
In many hydrological models, the amount of evapotranspired water is calculated using the potential evapotranspiration (PET) approach. The main driver of several PET approaches is net radiation, whose downward components are usually obtained from meteorological input data, whereas the upward components are calculated by the model itself. Thus, uncertainties can be large due to both the input data and model assumptions. In this study, we compare the radiation components of the WaterGAP Global Hydrology Model, driven by two meteorological input datasets and two radiation setups from ERA-Interim reanalysis. We assess the performance with respect to monthly observations provided by the Baseline Surface Radiation Network (BSRN) and the Global Energy Balance Archive (GEBA). The assessment is done for the global land area and specifically for energy/water limited regions. The results indicate that there is no optimal radiation input throughout the model variants, but standard meteorological input datasets perform better than those directly obtained by ERA-Interim reanalysis for the key variable net radiation. The low number of observations for some radiation components, as well as the scale mismatch between station observations and 0.5° × 0.5° grid cell size, limits the assessment.
The Earth's future depends on how we manage the manifold risks of climate change (CC). It is state-of-the-art to assume that risk reduction requires participatory management involving a broad range of stakeholders and scientists. However, there is still little knowledge about the optimal design of participatory climate change risk management processes (PRMPs), in particular with respect to considering the multitude of substantial uncertainties that are relevant for PRMPs. To support the many local to regional PRMPs that are necessary for a successful global-scale reduction of CC risks, we present a roadmap for designing such transdisciplinary knowledge integration processes. The roadmap suggests ways in which uncertainties can be comprehensively addressed within a PRMP. We discuss the concept of CC risks and their management and propose an uncertainty framework that distinguishes epistemic, ontological, and linguistic uncertainty as well as ambiguity. Uncertainties relevant for CC risk management are identified. Communicative and modeling methods that support social learning as well as the development of risk management strategies are proposed for each of six phases of a PRMP. Finally, we recommend how to evaluate PRMPs as such evaluations and their publication are paramount for achieving a reduction of CC risks.
The present PhD thesis comprises structural geology, petrographic and geochronological investiga-tions on crystalline rocks of the Uppermost Unit in the southern Aegean realm. Studies were carried out in three areas: (1) on the island of Anafi, (2) in the area west of Melambes in central Crete and (3) between the villages of Pefkos, Kalami and Sykologos in the municipality of Viannos in eastern Crete.
The Uppermost Unit forms together with the underlying, non-metamorphic Pindos Unit the upper nappe system of the Cretan nappe pile that, unlike the units of the lower nappe system, was not affected by Late Oligocene to Early Miocene subduction-related metamorphism. The upper nappe system must therefore have been at upper levels of the lithosphere in the Late Oligocene. This is of particular im-portance when reconstructing the tectonometamorphic evolution of the Uppermost Unit. The Upper-most Unit is very heterogeneous in composition and is subdivided into several subunits, which differ mainly in their lithological composition and the degree of metamorphic overprint. Usually, it is subdi-vided into several low-grade metamorphic subunits and one high-grade metamorphic subunit. Within the scope of this PhD thesis, three of these subunits were examined; (1) the anchimetamorphic Arvi Unit, (2) the newly described Greenschist Unit and (3) the Asterousia Crystalline Complex (ACC).
The analyses conducted during this PhD thesis include: (1) structural geology investigations in the field, (2) microstructural and petrographic analyses on thin sections, (3) radiometric dating of zircons using isotope dilution thermal ionisation mass spectrometry (ID-TIMS) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), (4) electron microprobe (EMP) analysis, (5) quartz texture analysis using electron-backscattered diffraction (EBSD), (6) semiquantitative analysis of min-eral phases using X-ray powder diffraction (XRD), (7) analysis of the modal composition of intrusive rocks applying point counting on thin sections and (8) X-ray microtomography (micro-CT) on chias-tolite hornfels.
...
Binary nucleation of sulphuric acid-water particles is expected to be an important process in the free troposphere at low temperatures. SAWNUC (Sulphuric Acid Water Nucleation) is a model of binary nucleation that is based on laboratory measurements of the binding energies of sulphuric acid and water in charged and neutral clusters. Predictions of SAWNUC are compared for the first time comprehensively with experimental binary nucleation data from the CLOUD chamber at European Organization for Nuclear Research. The experimental measurements span a temperature range of 208–292 K, sulphuric acid concentrations from 1·106 to 1·109 cm−3, and distinguish between ion-induced and neutral nucleation. Good agreement, within a factor of 5, is found between the experimental and modeled formation rates for ion-induced nucleation at 278 K and below and for neutral nucleation at 208 and 223 K. Differences at warm temperatures are attributed to ammonia contamination which was indicated by the presence of ammonia-sulphuric acid clusters, detected by an Atmospheric Pressure Interface Time of Flight (APi-TOF) mass spectrometer. APi-TOF measurements of the sulphuric acid ion cluster distributions (math formula with i = 0, 1, ..., 10) show qualitative agreement with the SAWNUC ion cluster distributions. Remaining differences between the measured and modeled distributions are most likely due to fragmentation in the APi-TOF. The CLOUD results are in good agreement with previously measured cluster binding energies and show the SAWNUC model to be a good representation of ion-induced and neutral binary nucleation of sulphuric acid-water clusters in the middle and upper troposphere.
Chemical reduction-oxidation mechanisms within mantle rocks link to the terrestrial carbon cycle by influencing the depth at which magmas can form, their composition, and ultimately the chemistry of gases released into the atmosphere. The oxidation state of the uppermost mantle has been widely accepted to be unchanged over the past 3800 m.y., based on the abundance of redox-sensitive elements in greenstone belt–associated samples of different ages. However, the redox signal in those rocks may have been obscured by their complex origins and emplacement on continental margins. In contrast, the source and processes occurring during decompression melting at spreading ridges are relatively well constrained. We retrieve primary redox conditions from metamorphosed mid-oceanic ridge basalts (MORBs) and picrites of various ages (ca. 3000–550 Ma), using V/Sc as a broad redox proxy. Average V/Sc values for Proterozoic suites (7.0 ± 1.4, 2σ, n = 6) are similar to those of modern MORB (6.8 ± 1.6), whereas Archean suites have lower V/Sc (5.2 ± 0.4, n = 5). The lower Archean V/Sc is interpreted to reflect both deeper melt extraction from the uppermost mantle, which becomes more reduced with depth, and an intrinsically lower redox state. The pressure-corrected oxygen fugacity (expressed relative to the fayalite-magnetite-quartz buffer, ΔFMQ, at 1 GPa) of Archean sample suites (ΔFMQ –1.19 ± 0.33, 2σ) is significantly lower than that of post-Archean sample suites, including MORB (ΔFMQ –0.26 ± 0.44). Our results imply that the reducing Archean atmosphere was in equilibrium with Earth’s mantle, and further suggest that magmatic gases crossed the threshold that allowed a build-up in atmospheric O2 levels ca. 3000 Ma, accompanied by the first “whiffs” of oxygen in sediments of that age.
We have developed and characterized the novel PTR3, a proton transfer reaction-time-of-flight mass spectrometer (PTR-TOF) using a new gas inlet and an innovative reaction chamber design. The reaction chamber consists of a tripole operated with rf voltages generating an electric field only in the radial direction. An elevated electrical field is necessary to reduce clustering of primary hydronium (H3O+) and product ions with water molecules present in the sample gas. The axial movement of the ions is achieved by the sample gas flow only. Therefore, the new design allows a 30-fold longer reaction time and a 40-fold increase in pressure compared to standard PTR-TOF-MS. First calibration tests show sensitivities of up to 18000 counts per second/parts per billion and volume (cps/ppbv) at a mass resolution of >8000 m/Δm (fwhm). The new inlet using center-sampling through a critical orifice reduces wall losses of low volatility compounds. Therefore, the new PTR3 instrument is sensitive to VOC typically present in the ppbv range as well as to semivolatile organic compounds (SVOC) and even highly oxidized organic molecules (HOMs) present in the parts per quadrillion per volume (ppqv) range in the atmosphere.
The Global Irrigation Model (GIM) is used within the framework of the global hydrological model WaterGAP to calculate monthly irrigation crop water use. Results on a 0.5 degrees grid include, consumption (ICU) and, via division by irrigation efficiencies, water withdrawal (IWU). The model distinguishes up to two cropping periods of rice and non-rice crops, each grown for 150 days, using a grid of area equipped for irrigation (AEI). Historical development of AEI and fraction of area actually irrigated (AAI) was previously considered via scaling of cell-specific results with country-specific factors for each year. In this study, GIM was adapted to use the new Historical Irrigation Data set (HID) with cell-specific AEI for 14 time slices between 1900 and 2005. AEI grids were temporally interpolated, and using the optional grid of AAI/AEI, results for years 1901-2014 were generated (runs "HID-ACT"). Thus, new installation or abandonment of irrigation infrastructure in new grid cells can be represented in a spatially explicit manner. For evaluated years 1910, 1960, 1995, and 2005, ICU from HID-ACT was superior to country-specific scaled results (run "HID-ACTHIST") in representing historical development of the spatial pattern. Compared to US state-level reference data, spatial patterns were better, while country totals were not always better. For calculating the cropping periods, 30-years climate means are needed, the choice of which is relevant. Four chosen periods before 1981-2010 all resulted in considerable, pertaining changes of ICU spatial pattern, and various percent changes in country totals. This might be because of already present climate change.
This study examines the urban heat island (UHI) of Brussels, for both current (2000–2009) and projected future (2060–2069) climate conditions, by employing very high resolution (250 m) modelling experiments, using the urban boundary layer climate model UrbClim. Meteorological parameters that are related to the intensity of the UHI are identified and it is investigated how these parameters and the magnitude of the UHI evolve for two plausible trajectories for future climate conditions. UHI intensity is found to be strongly correlated to the inversion strength in the lowest 100 m of the atmosphere. The results for the future scenarios indicate that the magnitude of the UHI is expected to decrease slightly due to global warming. This can be attributed to the increased incoming longwave radiation, caused by higher air temperature and humidity values. The presence of the UHI also has a significant impact on the frequency of extreme temperature events in the city area, both in present and future climates, and exacerbates the impact of climate change on the urban population as the amount of heat wave days in the city increases twice as fast as in the rural surroundings.
Das Ziel dieser Arbeit ist die Untersuchung der stratosphärischen Meridionalzirkulation mit Hilfe von chemisch aktiven Spurengasen. Diese motiviert sich durch die Tatsache, dass der Klimawandel neben den viel erforschten Auswirkungen auf die Troposphäre, auch Reaktionen in der Stratosphäre zur Folge hat, welche bisher weit weniger tiefgehend untersucht wurden. Das macht die Stratosphäre zu einem aktuellen und frequentierten Forschungsgebiet der experimentellen und theoretischen Meteorologie. Neben vereinzelten hochaufgelösten in-situ Messungen und globalen Satellitendaten sind es hier vor allem globale numerische Klima-Chemiemodelle, die für Analysen genutzt werden. Für diese Arbeit wurden Daten des EMAC-Modells (engl.: ECHAM/MESSy Atmospheric Chemistry) ausgwertet, welche im Rahmen der ESCiMo (engl.: Earth System Chemistry integrated Modelling) Initiative vom MESSy-Konsortium (engl.: Modular Earth Submodel System) erstellt wurden. Die Zielsetzung dieser Arbeit war, ob sich etwaige Änderungen des stratosphärischen Transports anhand von modellierten, chemisch aktiven, idealisierten Spurengasen feststellen lassen. Idealisiert bedeutet hierbei, dass diese Gase ein konstantes Mischungsverhältnis am Erdboden aufweisen und den identischen chemischen Prozessen unterliegen wie die realistischen Tracer. Dies hat zur Folge, dass diese Spurengase somit nicht in das Strahlungsbudget des Modells rückkoppeln und ihre Verteilung nicht durch zeitliche troposphärische Trends beeinflusst wird. Zur Analyse des stratosphärischen Transports wurden die Differenzen der monatlich gemittelten Mischungsverhältnisse zweier Zeitpunkte der verschiedenen Substanzen im Vertikalprofil betrachtet und ausgewertet, wobei hier die photolytische Lebenszeit und die Zeitskala des Transports zu berücksichtigen war. Um die Saisonalität von Transport und Chemie zu berücksichtigen, wurden dazu die Monate März, Juni, September und Dezember analysiert.
Die Resultate zeigten, dass chemisch aktive Substanzen in der Tat geeignet sind Änderungen in der Dynamik festzustellen. So stellte sich heraus, dass mit einer allgemeinen Intensivierung der stratosphärischen Meridionalzirkulation im kommenden Jahrhundert gerechnet werden kann, wobei hiervon besonders die untere Stratosphäre betroffen ist. Eine Differenzierung welche Komponente der Zirkulation (Residualtransport oder bidirektionale quasi-horizontale Mischung) hierbei von übergeordneter Bedeutung ist, konnte nicht spezifiziert werden. Um abzuschätzen, ob sich die Änderung der Zirkulation durch Änderungen in den Mischungsverhältnissen von chemisch aktiven Substanzen mit Hilfe von direkten Messungen nachweisen lässt, wurde die atmosphärische Variabilität des Modells bestimmt und mit den Veränderungen dieser Mischungsverhältnisse verglichen. Es zeigte sich, dass diese modellierte atmosphärische Variabilität zum Teil deutlich größer war, als die Differenzen der Mischungsverhältnisse und so ohne eine Vielzahl von in-situ Messungen keine eindeutige Aussage zulassen. Um eine statistisch valide Aussage treffen zu können, müssen daher mehrere Messreihen innerhalb eines Monats durchgeführt werden. Zudem stellte sich heraus, dass der Monat Juni der bestmögliche Messzeitraum ist, da hier die natürliche Variabilität am geringsten ist. Zuletzt wurden die Spurengase mit vergleichsweise kleiner chemischer Lebenszeit auf normierten N2O-Isoplethen untersucht und die Verschiebung dieser Kurve zwischen den zwei Zeitpunkten analysiert. Die so gewonnenen Resultate ließen den Schluss zu, dass sich auf diese Weise die atmosphärische Variabilität reduzieren lässt und bei Nutzung mit experimentellen Daten eine zu den Tracer-Differenzen konsistente Aussage zulässt. So bestärkte diese Methode die These, dass sich der stratosphärische Transport innerhalb des 21. Jahrhunderts wahrscheinlich verstärken wird.
Evidence of widespread wildfires in a coal seam from the middle Permian of the North China Basin
(2017)
The North China Basin is the largest coal-bearing basin in China, and has an areal extent of 800,000 km2. We analyzed 138 coal samples and in situ pillar coal samples of the middle Permian from this basin by macropetrography, microscope, scanning electron microscope, gas chromatography, and gas chromatography–mass spectrometer in order to study wildfires. High contents of inertinite (charcoal) and natural coke particles observed in coal samples indicate that vegetation in precursor mires and peats of the middle Permian coal from north China was exposed to far-ranging wildfires. In addition, high-molecular-weight polycyclic aromatic hydrocarbons were detected in the coal samples. These aromatic compounds were formed under high temperatures and provide further evidence of wildfire. These wildfires would have discharged significant CO and CO2 gases into the atmosphere and affected the paleoclimate and paleoecosystem.
Coccolithophores are an abundant phytoplankton group that exhibit remarkable diversity in their biology, ecology and calcitic exoskeletons (coccospheres). Their extensive fossil record is a testament to their important biogeochemical role and is a valuable archive of biotic responses to environmental change stretching back over 200 million years. However, to realise the full potential of this archive for (palaeo-)biology and biogeochemistry requires an understanding of the physiological processes that underpin coccosphere architecture. Using culturing experiments on four modern coccolithophore species (Calcidiscus leptoporus, Calcidiscus quadriperforatus, Helicosphaera carteri and Coccolithus braarudii) from three long-lived families, we investigate how coccosphere architecture responds to shifts from exponential (rapid cell division) to stationary (slowed cell division) growth phases as cell physiology reacts to nutrient depletion. These experiments reveal statistical differences in coccosphere size and the number of coccoliths per cell between these two growth phases, specifically that cells in exponential-phase growth are typically smaller with fewer coccoliths, whereas cells experiencing growth-limiting nutrient depletion have larger coccosphere sizes and greater numbers of coccoliths per cell. Although the exact numbers are species-specific, these growth-phase shifts in coccosphere geometry demonstrate that the core physiological responses of cells to nutrient depletion result in increased coccosphere sizes and coccoliths per cell across four different coccolithophore families (Calcidiscaceae, Coccolithaceae, Isochrysidaceae and Helicosphaeraceae), a representative diversity of this phytoplankton group. Building on this, the direct comparison of coccosphere geometries in modern and fossil coccolithophores enables a proxy for growth phase to be developed that can be used to investigate growth responses to environmental change throughout their long evolutionary history. Our data also show that changes in growth rate and coccoliths per cell associated with growth-phase shifts can substantially alter cellular calcite production. Coccosphere geometry is therefore a valuable tool for accessing growth information in the fossil record, providing unprecedented insights into the response of species to environmental change and the potential biogeochemical consequences.
When assessing global water resources with hydrological models, it is essential to know the methodological uncertainties in the water resources estimates. The study presented here quantifies effects of the uncertainty in the spatial and temporal patterns of meteorological variables on water balance components at the global, continental and grid cell scale by forcing the global hydrological model WaterGAP 2.2 (ISI-MIP 2.1) with five state-of-the-art climate forcing input data-sets. While global precipitation over land during 1971–2000 varies between 103 500 and 111 000 km3 yr−1, global river discharge varies between 39 200 and 42 200 km3 yr−1. Temporal trends of global wa- ter balance components are strongly affected by the uncertainty in the climate forcing (except human water abstractions), and there is a need for temporal homogenization of climate forcings (in particular WFD/WFDEI). On about 10–20 % of the global land area, change of river discharge between two consecutive 30 year periods was driven more strongly by changes of human water use including dam construction than by changes in precipitation. This number increases towards the end of the 20th century due to intensified human water use and dam construction. The calibration approach of WaterGAP against observed long-term average river discharge reduces the impact of climate forcing uncertainty on estimated river discharge significantly. Different homgeneous climate forcings lead to a variation of Q of only 1.6 % for the 54 % of global land area that are constrained by discharge observations, while estimated renewable water resources in the remaining uncalibrated regions vary by 18.5 %. Uncertainties are especially high in Southeast Asia where Global Runoff Data Centre (GRDC) data availability is very sparse. By sharing already available discharge data, or installing new streamflow gauging stations in such regions, water balance uncertainties could be reduced which would lead to an improved assessment of the world’s water resources.
Ice nucleating particles over the Eastern Mediterranean measured by unmanned aircraft systems
(2016)
During an intensive field campaign on aerosol, clouds and ice nucleation in the Eastern Mediterranean in April 2016, we have measured the abundance of ice nucleating particles (INP) in the lower troposphere from unmanned aircraft systems (UAS). Aerosol samples were collected by miniaturized electrostatic precipitators onboard the UAS at altitudes up to 2.5 km. The number of INP in these samples, which are active in the deposition and condensation modes at temperatures from −20 to −30 ◦C, were analyzed immediately after collection on site using the ice nucleus counter FRIDGE. During the one month campaign we encountered a series of Saharan dust plumes that traveled at several kilometers altitude. Here we present INP data from 42 individual flights, together with aerosol number concentrations, observations of lidar backscattering, dust concentrations derived by the dust transport model DREAM (Dust Regional Atmospheric Model), and results from scanning electron microscopy. The effect of the dust plumes is reflected by the coincidence of INP with the particulate mass (PM), the lidar signal and with the predicted dust mass of the model. This suggests that mineral dust or a constituent related to dust was a major contributor to the ice nucleating properties of the aerosol. Peak concentrations of above 100 INP std.l -1 were measured at −30 ◦C. The INP concentration in elevated plumes was on average a factor of 10 higher than at ground level. Since desert dust is transported for long distances over wide areas of the globe predominantly at several km altitude we conclude that INP measurements at ground level may be of limited significance for the situation at the level of cloud formation.
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 determine mean age. We present balloon-borne AirCore observations from two midlatitude sites: Timmins in Ontario/Canada and Lindenberg in Germany. During the Timmins campaign, five AirCores sampled air in parallel with 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 Hemisphere midlatitudes. The time series now covers more than 40 years and shows a small, statistically non-significant positive trend of 0.15 ± 0.18 years decade−1. This trend is slightly smaller than the previous estimate of 0.24 ± 0.22 years decade−1 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.
AirCore-HR : a high-resolution column sampling to enhance the
vertical description of CH₄ and CO₂
(2017)
An original and innovative sampling system called AirCore was presented by NOAA in 2010 (Karion et al., 2010). It consists of a long ( > 100 m) and narrow (< 1 cm) stainless steel tube that can retain a profile of atmospheric air. The captured air sample has then to be analyzed with a gas analyzer for trace mole fraction. In this study, we introduce a new AirCore aiming to improve resolution along the vertical with the objectives to (i) better capture the vertical distribution of CO2 and CH4, (ii) provide a tool to compare AirCores and validate the estimated vertical resolution achieved by AirCores. This (high-resolution) AirCore-HR consists of a 300 m tube, combining 200 m of 0.125 in. (3.175 mm) tube and a 100 m of 0.25 in. (6.35 mm) tube. This new configuration allows us to achieve a vertical resolution of 300 m up to 15 km and better than 500 m up to 22 km (if analysis of the retained sample is performed within 3 h). The AirCore-HR was flown for the first time during the annual StratoScience campaign from CNES in August 2014 from Timmins (Ontario, Canada). High-resolution vertical profiles of CO2 and CH4 up to 25 km were successfully retrieved. These profiles revealed well-defined transport structures in the troposphere (also seen in CAMS-ECMWF high-resolution forecasts of CO2 and CH4 profiles) and captured the decrease of CO2 and CH4 in the stratosphere. The multi-instrument gondola also carried two other low-resolution AirCore-GUF that allowed us to perform direct comparisons and study the underlying processing method used to convert the sample of air to greenhouse gases vertical profiles. In particular, degrading the AirCore-HR derived profiles to the low resolution of AirCore-GUF yields an excellent match between both sets of CH4 profiles and shows a good consistency in terms of vertical structures. This fully validates the theoretical vertical resolution achievable by AirCores. Concerning CO2 although a good agreement is found in terms of vertical structure, the comparison between the various AirCores yields a large and variable bias (up to almost 3 ppm in some parts of the pro- files). The reasons of this bias, possibly related to the drying agent used to dry the air, are still being investigated. Finally, the uncertainties associated with the measurements are assessed, yielding an average uncertainty below 3 ppb for CH4 and 0.25 ppm for CO2 with the major source of uncertainty coming from the potential loss of air sample on the ground and the choice of the starting and ending point of the collected air sample inside the tube. In an ideal case where the sample would be fully retained, it would be possible to know precisely the pressure at which air was sampled last and thus to improve the overall uncertainty to about 0.1 ppm for CO2 and 2 ppb for CH4
Recent analysis of long-term balloon-borne measurements of Antarctic stratospheric condensation nuclei (CN) and temperature combined with global model calculations showed the wide extent of a mid stratospheric layer of new particles. Here the nucleation model SAWNUC is used to derive Antarctic stratospheric gaseous sulfuric acid profiles and to investigate the nucleation process of this CN layer. The sulfuric acid profiles were derived for an altitude range of 18-32 km between July and October by simulating air parcel trajectories that descend inside the polar vortex and calculating the sulfuric acid amount that reproduces the observations. The derived sulfuric acid concentrations (volume mixing ratios) are of the order of magnitude of 104 cm-3 (10-14) in July. In the following months the concentrations increase to about 107 cm-3 (10 exp -11) in October. They depend strongly on the temperature because a given temperature leaves only a small sulfuric acid range to reproduce the observed magnitude of CN. Ion-induced nucleation occurs. However, while it dominates nucleation at higher temperatures it has no significant influence on the nucleation rates at lower temperatures. Preexisting particles significantly reduce nucleation at sulfuric acid mixing ratios below 1 ppt. First estimates of sulfuric acid production rates range from 0.5 to about 500 molecules cm-3 s-1. A production mechanism for gaseous sulfuric acid during the Antarctic winter seems to be necessary to fully explain the observations. The derived sulfuric acid profiles compare well with midlatitude and Arctic sulfuric acid concentrations.
Nucleation modeling of the Antarctic stratospheric CN layer and derivation of sulfuric acid profiles
(2017)
Recent analysis of long-term balloon-borne measurements of Antarctic stratospheric condensation nuclei (CN) between July and October showed the formation of a volatile CN layer at 21–27 km altitude in a background of existing particles. We use the nucleation model SAWNUC to simulate these CN in subsiding air parcels and study their nucleation and coagulation characteristics. Our simulations confirm recent analysis that the development of the CN layer can be explained with neutral sulfuric acid–water nucleation and we show that outside the CN layer the measured CN concentrations are well reproduced just considering coagulation and the subsidence of the air parcels. While ion-induced nucleation is expected as the dominating formation process at higher temperatures, it does not play a significant role during the CN layer formation as the charged clusters recombine too fast. Further, we derive sulfuric acid concentrations for the CN layer formation. Our concentrations are about 1 order of magnitude higher than previously presented concentrations as our simulations consider that nucleated clusters have to grow to CN size and can coagulate with preexisting particles. Finally, we calculate threshold sulfuric acid profiles that show which concentration of sulfuric acid is necessary for nucleation and growth to observable size. These threshold profiles should represent upper limits of the actual sulfuric acid outside the CN layer. According to our profiles, sulfuric acid concentrations seem to be below midlatitude average during Antarctic winter but above midlatitude average for the CN layer formation.
Der "Regionalatlas Rhein-Main" wird zum 75-jährigen Jubiläum der "Rhein-Mainischen Forschung" veröffentlicht. Er verfolgt das Ziel,
- einne Überblick über die regionale Struktur des Rhein-Main-Gebietes zu verschaffen,
- Politik, Wirtschaft und Verwaltung Grundlagendaten in regionalisierter Form für ihre Entscheidungen an die Hand zu geben, und
- den im Rhein-Main-Gebiet lebenden Menschen die regionalen Strukturen ihres Lebensraumes näher zu bringen.
Im Rahmen einer Zusammenarbeit zwischen der Thüringer Landesanstalt für Umwelt und Geologie und der Goethe-Universität Frankfurt fand in Kooperation mit dem Deutschen Wetterdienst (DWD) eine umfassende Studie zum konvektiven Unwetterpotential über Thüringen statt. Unwetterereignisse, die durch konvektive Prozesse in der Atmosphäre verursacht werden, besitzen ein nicht unerhebliches Schadenspotential, obwohl sie oftmals eine räumlich eng begrenzte Ausdehnung aufweisen. Aufgrund ihrer Charakteristik ist sowohl die Vorhersage solcher Ereignisse, als auch eine vollständige, systematische Erfassung für eine detaillierte Auswertung längerer Zeitreihen noch immer eine Herausforderung. Zusätzliches Interesse besteht in der Abschätzung der durch den Klimawandel abhängigen Entwicklung des zukünftigen Gefährdungspotentials konvektiver Unwetter. Für eine gezielte Untersuchung des Themenkomplexes ist eine Vielzahl unterschiedlicher Daten und Methoden verwendet worden. Mit Hilfe von Fernerkundungsdatensätzen wird ein räumlich differenziertes Gefährdungspotential über Thüringen nachgewiesen. Bedingt durch das Relief ist das Auftreten von Konvektion am häufigsten und intensivsten über dem südlichen Thüringer Wald und dessen Ostrand zu beobachten, während Nordthüringen eine deutlich geringere Aktivität solcher Unwetterereignisse aufweist. Eine Abschätzung mittels globaler Klimamodelle und daraus abgeleiteten Wetterlagen zeigt unter Berücksichtigung des RCP8.5 Klimaszenarios für die nahe Zukunft (2016-2045) eine Zunahme des Gefährdungspotentials durch konvektive Unwetter. Aufgrund des Anstiegs feuchter Wetterlagen (49 % auf 82 %) erhöht sich die Zunahme der Gefährdung für den Zeitraum 2071-2100 noch deutlicher. Im Vergleich zu diesem statistischen Ansatz nimmt die projizierte Gefährdung durch extreme Ereignisse erheblich zu (Faktor 6), wenn die Ergebnisse expliziter Simulationen konvektiver Ereignisse mit einem regionalen Klimamodell (mit horizontaler Gitterdistanz von 1 km) und eine Zunahme der Tage mit konvektiven Extremereignissen berücksichtigt werden. Ein Anstieg der Gefährdung durch konvektive Unwetter in der Zukunft ist wahrscheinlich. Eine Quantifizierung bleibt jedoch unsicher.
Laut jüdischem Kalender entstand die Welt vor genau 5778 Jahren, nach der Bibel vor 6021 Jahren. Doch als Forscher begannen, auf und in der Erde selbst nach Spuren ihres Alters zu suchen, mussten sie die Zahl immer weiter nach oben korrigieren. Nach heutigen Datierungsmethoden ist unser Planet zwischen 4,5 und 4,6 Milliarden Jahre alt.
The Earth’s surface condition we find today is a result of long exposure to metabolism of life forms. Particularly, molecular oxygen in the atmosphere is a feature which developed over time. The first substantial and lasting rise of atmospheric oxygen level happened ≈ 2.5 Ga ago, but localities are reported where transiently elevated oxygen levels appeared before this time-point. To trace the timing and circumstances of the earliest availability of free oxygen in the atmosphere is important to understand the habitats of early microbial life forms on Earth.
This thesis focuses to obtain information of oxygen levels and the related atmospheric cycling of metals in sediments of the 3.5 to 3.2 Ga Barberton Greenstone Belt. First, as iron was a ubiquitous constituent of Archean seawater, I investigated its isotopic composition in minerals of chemical sediments. Hereby, I tried to resolve the changes within the water basin on small scale sedimentary sequence cycles. Second, I focused on the minor constituents of Archean seawater. The Re-Os geochronologic system and the abundance patterns of the platinum-group elements were chosen to integrate information of oxygen promoted weathering of a large source area. To integrate information of a large time interval, the isotopes of uranium were investigated over a large stratigraphic section.
The two key findings of this thesis are:
• Quantitative oxidation of ferrous iron in surface layers of Paleoarchean seawater occurred during the onset and termination of hydrothermal FeIIaq delivery into shallow waters.
• Paleoarchean sedimentary successions of the Barberton Greenstone Belt lack any evidence of transient basin-scale oxygenation.
The Manzimnyama Iron Formation (IF, Fig Tree Group, Barberton Greenstone Belt, South Africa) has been deciphered to exist of cyclic stacks of lithostratigraphic units with varying amounts of iron oxide and carbonate minerals. In-situ femtosecond-Laser-Ablation ICP-MS iron isotope measurements showed that the majority of siderite (γ56Fe ≈ −0.5 ‰) precipitated directly from seawater of γ56Fe ≈ 0 ‰. Ferric iron from the surface layers is preserved in ≤ 1μ m hematite and in magnetite that has been grown within the consolidated sediment. During FeIIaq events, fine-grained hematite (γ56Fe ≈ 2.2 ‰) and magnetite (γ56Fe 0.5 to 0.8 ‰) indicate oxygen levels in surface waters of lower than 0.0002 μM. Upon onset and termination of iron oxide abundance, magnetite with γ56Fe ≈ 0 ‰ indicates that low concentrations of FeIIaq in surface waters were oxidized quantitatively. These observations demonstrate the existence of iron oxidation in Paleoarchean surface waters independent of FeIIaq concentration. This is the first investigation of Paleoarchean IF showing that lithostratigraphic cyclicity can be traced in iron isotopic composition of oxide minerals.
ID-ICP-MS measurement of Re, Ir, Ru, Pt and Pd, trace element (SF-ICP-MS) and ID-MCICP- MS uranium isotope determination have been applied to carbonaceous shale of the Mapepe Fm. (Fig Tree Group) after inverse Aqua Regia leaching and bulk digestion. The sediments reveal a silicified fraction which exhibits a seawater REE signature and a mixture of detrital and meteoritic PGE. Neither enrichment of the redox-sensitive elements Re or Mo nor fractionated uranium isotopes have been found on a stratigraphic interval of several hundred meters. The non-silica fraction shows no depletion of Re which indicates that the detrital material had no contact to oxidizing fluids. ID-TIMS measurements of Re and Os after the CrO3-SO4 Carius Tube method of two sample intervals showed that the Re-Os isotopic systems of the non-silica fractions are identical to two komatiite occurrences. Weltevreden Fm. and Komati Fm. rocks were uplifted, eroded and transported to the deep part of the sedimentary basin without any change to the Re-Os system. Negative fractionated uranium isotopes (γ238U = −0.41 ± 0.01 ‰) associated with detrital Ba-Cr-U occurrences suggest the existence of distal redox-processes that involve uranium species. This study demonstrates that over the time of exposure and deposition of the Mapepe Fm. sedimentation, free oxygen was not available for weathering in the catchment area.
Ice nucleating particles over the eastern mediterranean measured by unmanned aircraft systems
(2017)
During an intensive field campaign on aerosol, clouds, and ice nucleation in the Eastern Mediterranean in April 2016, we measured the abundance of ice nucleating particles (INPs) in the lower troposphere from unmanned aircraft systems (UASs). Aerosol samples were collected by miniaturized electrostatic precipitators onboard the UASs at altitudes up to 2.5 km. The number of INPs in these samples, which are active in the deposition and condensation modes at temperatures from −20 to −30 °C, were analyzed immediately after collection on site using the ice nucleus counter FRIDGE (FRankfurt Ice nucleation Deposition freezinG Experiment). During the 1-month campaign, we encountered a series of Saharan dust plumes that traveled at several kilometers' altitude. Here we present INP data from 42 individual flights, together with aerosol number concentrations, observations of lidar backscattering, dust concentrations derived by the dust transport model DREAM (Dust Regional Atmospheric Model), and results from scanning electron microscopy. The effect of the dust plumes is reflected by the coincidence of INPs with the particulate matter (PM), the lidar signal, and the predicted dust mass of the model. This suggests that mineral dust or a constituent related to dust was a major contributor to the ice nucleating properties of the aerosol. Peak concentrations of above 100 INPs std L−1 were measured at −30 °C. The INP concentration in elevated plumes was on average a factor of 10 higher than at ground level. Since desert dust is transported for long distances over wide areas of the globe predominantly at several kilometers' altitude, we conclude that INP measurements at ground level may be of limited significance for the situation at the level of cloud formation.
Geoelektrische Methoden sind weit verbreitet und werden häufig zur Erkundung des oberflächennahen Untergrundes eingesetzt. Angewendet werden standardmäßig meist nur linienhafte Anordnungen der Sender- und Empfängerelektroden, die nur wenige Zehner Meter lang sind. Hierdurch haben diese Methoden nur geringe Eindringtiefen. Um größere Eindringtiefen und 3-dimensionale Informationen über den Untergrund zu erhalten, sind in der vorgestellten Studie die Empfänger- und Senderdipole in mehr oder weniger regelmäßigen Abständen über das Untersuchungsgebiet verteilt worden. Mit jeder Empfängerstation sind kontinuierlich die elektrischen Spannungen in bis zu drei Richtungen aufgezeichnet worden. Für die Einspeisungen wurde ein Rechtecksignal verwendet, das sich gut von den Störfrequenzen und den natürlichen Spannungen abhebt. Die Richtungen der Einspeisedipole sind entsprechend den örtlichen Gegebenheiten, jedoch möglichst parallel zu den Messrichtungen, gewählt worden. Zur Auswertung der erhobenen Messdaten wurde ein Programmpaket entwickelt, das eine weitestgehend automatisierte Auswertung der Daten erlaubt. Die Bestimmung der scheinbaren spezifischen Widerstände und ihrer Messfehler wurde an den fouriertransformierten Datenzeitreihen durchgeführt. Hierdurch konnten Störeinflüsse minimiert werden und es wurde möglich selbst stark verrauschte Datensätze auszuwerten. Um die erhobenen Daten interpretieren zu können sind die berechneten scheinbaren spezifischen Widerstände als Grundlage für Inversionen und Modellstudien verwendet worden. Die oben beschriebene Methode wurde im Rahmen der vorliegenden Arbeit in zwei unterschiedlichen Messgebieten angewandt.
Messgebiet im Hohen Vogelsberg
Im Juli 2007 wurde damit begonnen, die Forschungsbohrung Sichenhausen-Eschwald im Hohen Vogelsberg abzuteufen. Ziel war es, Informationen über den strukturellen Aufbau des größten geschlossenen Vulkankomplexes Mitteleuropas zu gewinnen. Die Gesteinsansprache der Tiefbohrung lieferte bereits relativ früh Hinweise darauf, dass ein großer magmatischer Körper aufgeschlossen wurde.Aufgrund der begrenzten räumlichen Aussagekraft der Bohrung und fehlender Geländebefunde war es nicht möglich, den Mechanismus der Platznahme und die Größe des Körpers näher zu beschreiben. Die Kampagne hatte das Ziel diese Lücke zu schließen und ein 3-dimensionales Modell des Untergrundes zu erstellen.In dem annähernd quadratischen Untersuchungsgebiet, das eine Fläche von ca. 25 $km²$ aufweist, wurden 20 Datenlogger zur Aufzeichnung der elektrischen Spannungen aufgebaut. Die Empfängerdipole waren zwischen 20 m und 30 m lang. Insgesamt wurden 36 Stromeinspeisungen mit Stromstärken zwischen 28 A und 40 A an 16 unterschiedlichen Positionen für jeweils 2 bis 3 verschiedene Dipolrichtungen vorgenommen. Die Einspeisedipole waren zwischen 100 m und 300 m lang. Insgesamt konnten 1.439 scheinbare spezifische Widerstände berechnet werden.Die Ergebnisse der Modellierungen und der Inversion der Daten zeigen, dass mit der Forschungsbohrung ein domartiger Körper angebohrt wurde. Anhand der Ergebnisse kann die räumliche Ausdehnung des Körpers eingegrenzt und ein vorher noch nicht kartierter Gang nachgewiesen werden.
Messgebiet im Bereich der Kinzigtalsperre
Das etwa Ost-West verlaufende Kinzigtal bildet die naturräumliche und geologische Grenze zwischen dem vulkanischen Vogelsberg im Norden und dem, in diesem Bereich aus Sedimentgesteinen aufgebauten, Spessart im Süden.Die zwischen Steinau a. d. Str. und Bad Soden-Salmünster befindliche Kinzigtalsperre dient dem Hochwasserschutz und der Regulierung des Pegels der Kinzig bei Dürreperioden. Der aufgestaute See ist relativ flach und weist im Normalstau maximale Tiefen von ca. 6~m auf. Der Stausee ist jedoch über weite Teile etwa 4~m tief. In dieser Kampagne betrug der Abstand zwischen den einzelnen Empfängerstationen etwa 100 m bis 300 m. Es wurde aufgrund der beengten Platzverhältnisse eine Dipollänge von ca. 48 m für die Einspeise- und die Empfängerdipole im Messgebiet gewählt. Insgesamt wurden 14 Empfängerstationen im Messgebiet aufgebaut, von denen sich Neun auf dem Seegrund befanden. Das Messraster orientierte sich am vermuteten Verlauf der Kinzigtalstörung. An 8 Positionen sind in 21 Richtungen elektrische Ströme mit Stärken zwischen 2,2 A und 40 A in den Untergrund eingespeist worden. Es konnten 536 scheinbare spezifische Widerstände berechnet werden. Ziel war es, den Verlauf der Störung näher zu bestimmen und die Tiefe der im Untergrund vorhandenen salinären Grundwässer zu bestimmen. Die Bestimmung des Verlaufs der Kinzigtalstörung sowie die Tiefenbestimmung der salinären Grundwässer war mit den erhobenen Daten jedoch nicht möglich.
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.