Search results for "stoffe"
showing 10 items of 71 documents
Cross-hemispheric transport of central African biomass burning pollutants: implications for downwind ozone production
2010
Pollutant plumes with enhanced concentrations of trace gases and aerosols were observed over the southern coast of West Africa during August 2006 as part of the AMMA wet season field campaign. Plumes were observed both in the mid and upper troposphere. In this study we examined the origin of these pollutant plumes, and their potential to photochemically produce ozone (O<sub>3</sub>) downwind over the Atlantic Ocean. Their possible contribution to the Atlantic O<sub>3</sub> maximum is also discussed. Runs using the BOLAM mesoscale model including biomass burning carbon monoxide (CO) tracers were used to confirm an origin from central African biomass burning fires. The…
Recent progress in understanding physical and chemical properties of African and Asian mineral dust
2011
International audience; This paper presents a review of recently acquired knowledge on the physico-chemical properties of mineral dust from Africa and Asia based on data presented and discussed during the Third International Dust Workshop, held in Leipzig (Germany) in September 2008. Various regional field experiments have been conducted in the last few years, mostly close to source regions or after short-range transport. Although significant progress has been made in characterising the regional variability of dust properties close to source regions, in particular the mineralogy of iron and the description of particle shape and mixing state, difficulties remain in estimating the range of va…
Appearance and use of Roman roofing materials in the region of the Aedui and Lingones
2014
Römische Konstruktionstechniken und Baustoffe können als Anzeichen für Romanisierung gewertet werden. Sie legenZeugnis von den veränderten Verhaltensweisen ab, wie die Haeduer und die Lingonen mit den natürlichen Ressourcenumgingen, um diese Materialien zu produzieren. Es können deutliche Unterschiede zwischen diesen beiden gallischenStämmen hinsichtlich des Einsatzes von Ziegel- und Steindächern beobachtet werden. Die Haeduer verwenden meistensZiegel für ihre Dächer, selbst wenn die lokal verfügbaren natürlichen Ressourcen eine Produktion dieses Baustoffesnicht erlauben. Im Gegensatz dazu kommen bei den Lingonen Ziegel nur dann zum Einsatz, wenn die entsprechendenRessourcen vorhanden …
Impact of rocket exhaust plumes on atmospheric composition and climate – an overview
2013
Rockets are the only direct anthropogenic emission sources into the upper atmosphere. Gaseous rocket emissions include CO, N2, H2, H2O, and CO2, while solid rocket motors (SRM) additionally inject significant amounts of aluminum oxide (Al2O3) particles and gaseous chlorine species into the atmosphere. These emissions strongly perturb local at- mospheric trace gas and aerosol distributions. Here, the previous aircraft measurements in various rocket exhaust plumes including several large space shuttle launch vehicles are compiled. The observed changes of the lower stratospheric composition in the near field are summarized.
Initial approaches in benchmarking and round robin testing for proton exchange membrane water electrolyzers
2019
Abstract As ever-increasing amounts of renewable electricity enter the energy supply mix on a regional, national and international basis, greater emphasis is being placed on energy conversion and storage technologies to deal with the oscillations, excess and lack of electricity. Hydrogen generation via proton exchange membrane water electrolysis (PEMWE) is one technology that offers a pathway to store large amounts of electricity in the form of hydrogen. The challenges to widespread adoption of PEM water electrolyzers lie in their high capital and operating costs which both need to be reduced through R&D. An evaluation of reported PEMWE performance data in the literature reveals that there …
Harmoniset funktiot kompleksialueessa ja konformikuvaukset
2014
Tämän tutkielman tarkoituksena on syventää tietoja kompleksianalyysistä tutustumalla harmonisiin funktioihin ja konformikuvauksiin. Funktioita, jotka toteuttavat Laplacen yhtälön, kutsutaan harmonisiksi funktioiksi. Harmonisten funktioiden määrittämiseen voidaan käyttää Cauchy-Riemannin yhtälöitä. Harmoniset funktioit ovat yhteydessä analyyttisiin funktioihin, sillä harmonisten funktioiden avulla voidaan selittää analyyttisten kuvausten teoriaa ja päinvastoin. Tämän tutkielman kannalta tärkeimpiä analyyttisiä kuvauksia ovat injektiiviset kuvaukset, jotka tunnetaan myös konformikuvauksina. Konformikuvaukset ovat alueiden välisiä kuvauksia, jotka säilyttävät kulmien suuruuden ja suunnan ja jo…
Thermodynamic correction of particle concentrations measured by underwing probes on fast-flying aircraft
2016
Particle concentration measurements with underwing probes on aircraft are impacted by air compression upstream of the instrument body as a function of flight velocity. In particular, for fast-flying aircraft the necessity arises to account for compression of the air sample volume. Hence, a correction procedure is needed to invert measured particle number concentrations to ambient conditions that is commonly applicable to different instruments to gain comparable results. In the compression region where the detection of particles occurs (i.e. under factual measurement conditions), pressure and temperature of the air sample are increased compared to ambient (undisturbed) conditions in certain …
Particle chemical properties in the vertical column based on aircraft observations in the vicinity of Cape Verde Islands
2011
During the second Saharan Mineral Dust Experiment (SAMUM-2) field campaign, particles with geometric diameters (d) between ∼0.1 and 25 μm were collected on board of the Deutsches Zentrum für Luft- und Raumfahrt (German Aerospace Center, DLR) Falcon aircraft. Size, chemical composition and mixing state of aerosols sampled (spatially and vertically resolved) along the West African coastline and in the Cape Verde Islands region were determined by electron microscopy. A pronounced layer structure of biomass-burning aerosol and desert dust was present for all days during the sampling period from 23 January to 6 February. The aerosol composition of the small particles (d < 0.5 μm) was highly v…
Solar radiative effects of a Saharan dust plume observed during SAMUM assuming spheroidal model particles
2011
The solar optical properties of Saharan mineral dust observed during the Saharan Mineral Dust Experiment (SAMUM) were explored based on measured size-number distributions and chemical composition. The size-resolved complex refractive index of the dust was derived with real parts of 1.51–1.55 and imaginary parts of 0.0008–0.006 at 550 nm wavelength. At this spectral range a single scattering albedo ω o and an asymmetry parameter g of about 0.8 were derived. These values were largely determined by the presence of coarse particles. Backscatter coefficients and lidar ratios calculated with Mie theory (spherical particles) were not found to be in agreement with independently measured lidar data.…
Transport of Antarctic stratospheric strongly dehydrated air into the troposphere observed during the HALO-ESMVal campaign 2012
2015
Abstract. Dehydration in the Antarctic winter stratosphere is a well-known phenomenon that is annually observed by satellites and occasionally observed by balloon-borne measurements. However, in situ measurements of dehydrated air masses in the Antarctic vortex are very rare. Here, we present detailed observations with the in situ and GLORIA remote sensing instrument payload aboard the German aircraft HALO. Strongly dehydrated air masses down to 1.6 ppmv of water vapor were observed as far north as 47° S in an altitude between 12 and 13 km in the lowermost stratosphere. The dehydration can be traced back to individual ice formation events above the Antarctic Peninsula and Plateau, where ice…