1,721,219 research outputs found
Anthropogenes Bromoform aus der industriellen Wasserbehandlung
Full text linkThe control and ban of man-made long-lived ozone-depleting substances (ODSs) by the Montreal Protocol is expected to result in the recovery of the stratospheric ozone layer in the course of the 21st century. However, short-lived ODSs, which belong to the very short-lived substances (VSLSs), are not controlled and also participate in stratospheric ozone depletion through catalytic cycles. VSLSs are produced naturally from macroalgae and phytoplankton, and anthropogenically as disinfection by-products (DBPs) from chemical treatment of industrial water. Chemical treatment of seawater, e.g. cooling water of coastal power plants, mainly produces brominated VSLSs, with bromoform as the major DBP. Bromoform is also the largest source of organic bromine from biological marine sources to the atmosphere. However, the contribution of anthropogenic VSLSs to the global bromine budget is still unclear. Industrial water treatment has increased substantially over the last years due to strong economic growth and progressing industrialisation in East Asia and India. The increasing input of anthropogenic VSLSs from emerging industries to the environment has not been quantified yet. Given the growing importance of brominated VSLSs in the face of declining long-lived ODSs, a quantification of anthropogenic VSLS sources is urgently needed. The aim of this thesis is to quantify the environmental input of anthropogenic brominated VSLSs from industrial water treatment, their distribution in the ocean and atmosphere, and their entrainment into the stratosphere. The assessment focusses on the major DBP bromoform. The global distribution of anthropogenic bromoform sources serves as the initial release field for Lagrangian simulations of bromoform pathways in the ocean and atmosphere, and as the basis for air-sea flux calculations. Oceanic trajectory simulations are performed with the ARIANE software to analyse seasonal to annual variations of bromoform distribution. Atmospheric bromoform mixing ratios are simulated with the FLEXPART model in order to analyse the tropospheric and stratospheric distribution. Combining the climatological bottom-up air sea flux estimate with the bromoform flux from coastal power plants, the global bromine budget increases by 8–35 % to 1.9–2.2 Gmol Br a-1. Over 96 % of treated cooling water originate from the regions East-Southeast Asia, Europe, North America, India and Arabia. Bromoform is usually released close to its oceanic source. An effective transport into the stratosphere mainly takes place in the tropics, whereas in extratropical regions the majority of bromoform stays in the lower troposphere and is rapidly removed by deposition, e.g. in Europe. About half of the global anthropogenic bromoform is released in the region around East-Southeast Asia. The majority of this is discharged in the extratropics along the coasts of the Yellow, Japan and East China Seas. Still about 20 % of the bromoform from this region is entrained into the stratosphere during boreal winter due to transport towards the tropical West Pacific by northeasterly winds. The tropical West Pacific, as well as the Indian Ocean are the most efficient regions for stratospheric entrainment of bromoform. Over the Indian Ocean, tropical convection and the monsoon circulation during boreal summer transport 40–50 % of bromoform from the marine boundary layer to the stratosphere. Thereby, anthropogenic emissions contribute 10–43 % to stratospheric bromoform entrainment over the Indian Ocean, and 4–25 % over the global inner tropics. The anthropogenic sources of brominated VSLSs are predicted to increase in the future. In particular, increased bromoform emissions from growing industries in tropical regions will likely lead to more bromine input into the stratosphere. In order to reduce the uncertainties of DBP concentration in treated seawater, as well as the number of missing sources in the bromoform air-sea flux estimate, additional observations along the coasts close to the industrial areas are necessary. A better understanding of all natural and anthropogenic sources of brominated VSLSs and their future trends will thus improve estimates of the global atmospheric bromine input
SPARC 2017 - The SPARC Data Initiative: Assessment of stratospheric trace gas and aerosol climatologies from satellite limb sounders
No full textUpdate on Ozone Depleting Substances (ODSs) and Other Gases of Interest to the Montreal Protocol
Full text linkThis chapter concerns atmospheric changes in ozone-depleting substances (ODSs), such as chlorofluorocarbons (CFCs), halons, chlorinated solvents (e.g., carbon tetrachloride [CCl4] and methyl chloroform [CH3CCl3]) and hydrochlorofluorocarbons (HCFCs), which are controlled under the Montreal Protocol. Furthermore, the chapter updates information about ODSs not controlled under the Protocol, such as methyl chloride (CH3Cl) and very short-lived substances (VSLSs). In addition to depleting stratospheric ozone, many ODSs are potent greenhouse gases. Mole fractions of ODSs and other species are primarily measured close to the surface by global or regional monitoring networks. The surface data can be used to approximate a mole fraction representative of the global or hemispheric tropospheric abundance. Changes in the tropospheric abundance of an ODS result from a difference between the rate of emissions into the atmosphere and the rate of removal from it. The total amount of chlorine and bromine from ODSs that were controlled under the original Montreal Protocol is continuing to decline, as the overall emissions are smaller than the rate at which these ODSs are destroyed. Abundances of many of the first-stage replacement compounds, HCFCs, are now increasing very slowly or not at all.Fil: Laube, Johannes C.. Helmholtz Gemeinschaft. Forschungszentrum Jülich; AlemaniaFil: Tegtmeier, Susann. University of Saskatchewan; CanadáFil: Fernandez, Rafael Pedro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Interdisciplinario de Ciencias Básicas. - Universidad Nacional de Cuyo. Instituto Interdisciplinario de Ciencias Básicas; ArgentinaFil: Harrison, Jeremy. National Centre For Earth Observation; Reino UnidoFil: Hu, Lei. University of Colorado; Estados UnidosFil: Krummel, Paul. Csiro Oceans And Atmosphere.; AustraliaFil: Mahieu, Emmanuel. Université de Liège; BélgicaFil: Park, Sunyoung. Kyunpook National University; Corea del SurFil: Western, Luke. University Of Bristol
Investigations of gradient-drift and two-stream instabilities with analytical models and Particle-in-Cell simulations
Full text linkPlasmas with drifting electrons in crossed electric E and magnetic B field are used as ion sources in several applications including space propulsion and material processing. Despite long history, the nature of plasma instabilities in specific systems remains obscure. Gradient drift modes driven by combinations of the electron E×B drift and density gradient have been considered as one of the primary sources of fluctuations. In this work, we have verified the linear instability criteria for three possible regimes: ion-acoustic, modified two-stream, and electron cyclotron drift modes without the effect of the density gradients. For plasma parameters of interest for electric propulsion, we have studied the effects of finite values of the wave vector along the magnetic field and investigated the broadening and overlap of the cyclotron resonances and the transitions toward the ion-acoustic regime.
Studying the influence of density gradient on the Electron Cyclotron Drift Instability (ECDI), we show that for purely azimuthal modes, instabilities are enhanced for negative gradient density, while the positive gradients reduce growth rates. The lower-hybrid modes, which are a special case of more general ECDI, are then studied by eigenfrequencies analysis from the kinetic theory and comparison with an advanced fluid model, verifying the validity of the fluid model for different limits. The results indicate that in linear stage, the growth rates from the fluid model agree well with the kinetic theory.
This research also looks at the linear and nonlinear aspects of Buneman instability in magnetized and unmagnetized plasma, as a limit of ECDI. In this regard, the 1D (one-dimensional) particle in cell (PIC) simulations in the limit of cold electrons for the magnetized case are performed. The linear stage of the instability agrees well with the theoretical prediction. In the case of unmagnetized Buneman instability, it is found that in the regime of low drift velocity, the growth rate of the linear stage of the instability in 1D-PIC simulations differs significantly from the theoretical results. Hereof a series of highly resolved PIC simulations are performed with two different PIC codes. The initial noise due to particle discreteness is identified as a cause for discrepancies. The results of the performed simulations reveal that, although a quiet start scheme does not entirely solve the noise issue in PIC simulation, it improves the accuracy of linear growth rates
- …
