Sulfataerosole in einem urbanen Gebiet (Wien)

Zusammenfassung An einer stark befahrenen Straße in Wien wurden Messungen der Korngrößenverteilung des Staubes und der Sulfataerosole mittels 9stufiger Kaskadenimpaktoren durchgeführt. An derselben Meßstelle wurden Tagesgänge der Konzentrationen von Staub und wasserlöslichem Sulfat ermittelt. Parallel dazu wurden die Konzentrationen von SO₂ (relativkonduktometrisch) und Ozon (Chemilumineszenzmethode) sowie die Parameter Temperatur und relative Feuchte registriert. Die 36 Tagesgänge mit einer Dauer von je 36 Stunden wurden zu gleichen Teilen im Winter- und Sommerhalbjahr 1978/79 gemessen. In allen Fällen wurde das SO₄ ^2– nach Eluierung mit Wasser photometrisch nach der Thorinmethode bestimmt. Das Maximum der Korngrößenverteilung der Sulfate liegt zwischen 0,5 und 1m, diejenige des Staubes zeigt eine deutliche Trennung in Coarse- und Accumulation-Mode. Innerhalb einer Höhe von 20 m wurde im Mittel keine Vertikalvariation der Korngrößenverteilung der Sulfate gefunden. Die geometrischen Mittelwerte der Staubkonzentration betragen im Sommer (Winter) 208 (265)g/m³, diejenigen der Sulfatkonzentration 8,7 (16,2)g SO₄ ^2–/m³. Die höchsten Sulfatwerte finden sich im Mittel untertags, Spitzenwerte der SO₄ ^2–-Konzentration (bis zu 80g/m³) traten bei nebeligen Wetterlagen auf. Ein eindeutiger Zusammenhang zwischen der Sulfatkonzentration und dem Ozongehalt sowie den meteorologischen Parametern wurde nicht gefunden, die Korrelation zwischen Sulfat- und SO₂-Konzentration ist gesichert positiv. Geschätzte Oxydationsraten liegen zwischen 0,5 und 4,5% SO₂/h.

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Sulfate aerosols in an urban field (Vienna)

Summary At a site beside a frequented street in the centre of Vienna measurements of the size-distribution of dust and sulfate aerosol were made using 9-stage-cascade-impactors. At the same site diurnal variations of the concentrations of dust (using a high-volume-sampler), water-soluble sulfates, SO₂ (conductumetric) and ozone (chemiluminescence method) and the variations of temperature and relative humidity were registrated. The time resolution was 2 hours. The 36 diurnal variations (each of them with a duration of 36 hours) are distributed over 1978/79. In all cases SO₄ ^2– was determined photometrically using the thorine-method. The size-distribution of dust shows the existence of coarse- and accumulation-mode. The maximum of the size-distribution of SO₄ ^2– is between 0.5 and 1m aerodyn. diam. No vertical variation of SO₄ ^2–-concentration could be observed up to a height of 20 m above ground. Geometric mean values of dust-concentration in summer (winter) are 208 (265)g/m³, of SO₄ ^2–-concentration 8.7 (16.2)g/m³. Highest values of SO₄ ^2–-concentration occured during daytime in the mean. High concentrations (up to 80g SO₄ ^2–/m³) yielded under foggy weather conditions. Correlations are positive between SO₄ ^2– and SO₂ but positive or negative or even missing between sulfate and O₃, relative humidity and temperature. Estimated oxidation rates are 0.5–4.5% SO₂/h.

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Vorgetragen beim 8. Internationalen Mikrochemischen Symposium in Graz, 25.–30. August 1980.     

Validation of flow simulation and gas combustion sub-models for the CFD-based prediction of NOx formation in biomass grate furnaces

While reasonably accurate in simulating gas phase combustion in biomass grate furnaces, CFD tools based on simple turbulence–chemistry interaction models and global reaction mechanisms have been shown to lack in reliability regarding the prediction of NO_x formation. Coupling detailed NO_x reaction kinetics with advanced turbulence–chemistry interaction models is a promising alternative, yet computationally inefficient for engineering purposes. In the present work, a model is proposed to overcome these difficulties. The model is based on the Realizable k–? model for turbulence, Eddy Dissipation Concept for turbulence–chemistry interaction and the HK97 reaction mechanism. The assessment of the sub-models in terms of accuracy and computational effort was carried out on three laboratory-scale turbulent jet flames in comparison with the experimental data. Without taking NO_x formation into account, the accuracy of turbulence modelling and turbulence–chemistry interaction modelling was systematically examined on Sandia Flame D and Sandia CO/H₂/N₂ Flame B to support the choice of the associated models. As revealed by the Large Eddy Simulations of the former flame, the shortcomings of turbulence modelling by the Reynolds averaged Navier–Stokes (RANS) approach considerably influence the prediction of the mixing-dominated combustion process. This reduced the sensitivity of the RANS results to the variations of turbulence–chemistry interaction models and combustion kinetics. Issues related to the NO_x formation with a focus on fuel bound nitrogen sources were investigated on a NH₃-doped syngas flame. The experimentally observed trend in NO_x yield from NH₃ was correctly reproduced by HK97, whereas the replacement of its combustion subset by that of a detailed reaction scheme led to a more accurate agreement, but at increased computational costs. Moreover, based on results of simulations with HK97, the main features of the local course of the NO_x formation processes were identified by a detailed analysis of the interactions between the nitrogen chemistry and the underlying flow field.