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64 CHAPTER 2. ATMOSPHERE AND REMOTE SENSING 2.4.7 Two-dimensional measurement of motorway emission plumes Participating scientist Irene Pundt, Kai Uwe Mettendorf Abstract A first Long-path Tom-DOAS experiment was carried out in April/May 2001 next to the German motorway A656 (between Heidelberg and Mannheim), as part of the BAB II campaign (Fiedler et al., 2001). From the measurements along 16 different light paths vertical profiles on both sides of the motorway as well as two-dimensional maps of the NO2, SO2 and ozone concentration distributions could be derived. Emission factors were calculated and compared to model simulations. Figure 2.31: Left: Tomographic setup used during a motorway emission campaign. From each telescope one light beam is directed successively towards the eight retro reflectors (circles). Right: NO2 motor vehicle emission plume perpendicular to a motorway (in ppbv). Black bar: Location of the motorway, chequered area: Experiment towers, wind direction: coming from the left. Background Traffic emissions are among the major sources for anthropogenic air pollution. Volatile compounds and nitrogen oxides (NOx) are, besides others, important components of these emissions. Vehicle emission factors are generally estimated by means of dynamometric test measurements, but they may change under real world conditions. Therefore, a couple of field studies, mostly performed inside tunnels, have been conducted. However, the air flow through tunnels is influenced by the moving cars, causing an artificial wind, which changes the traffic emissions. A more realistic approach to evaluate emission factors is to carry out measurements at an open road. Knowledge of vertical profiles on both sides of the road is necessary to calculate emission rates (in molecules s −1 m −1 ). Taking 2D images of the emission plume perpendicular to the line source can provide even more information than emission rates. 2D images can be used to validate 2D dispersion models, or in the case of short lived species, to validate 2D chemical transport models. Funding TOMDOAS (BMBF) Methods and results The tomographic arrangement consisted of two long path telescope sites (one at each side of the motorway), and eight retro reflector arrays (four on each side at different heights). Each of the telescopes emitted one light beam, which was successively directed to the different retro-reflectors. Altogether 16 different light paths were realised. 2D NO2 concentration distributions perpendicular to the motorway were derived for several time spans (right figure). Concentrations on the left-hand side of the figure represent the NO2 background abundance and the right-hand side the background concentration plus emissions. For the inversion, an algebraic reconstruction technique was used in combination with bilinear basis functions describing the distribution. The derived emission plumes are, within the errors, in good agreement with model expectations. To our knowledge, these are the first measurements of two dimensional sections of an emission plume from a line source. Using multibeam telescopes will increase the time resolution of the images from hours to minute ranges in the future. Outlook/Future work SO2 and HCHO emission rates are currently evaluated and compared to model simulations. Ozone distributions seem to be not consistent with model expectations. Further work is needed to understand the discrepancies. Main publication Pundt et al. [2005c], Laepple et al. [2004], Mettendorf [2005]
2.4. DOAS TOMOGRAPHY GROUP 65 2.4.8 Two dimensional concentration distributions of a NO2 Emission plume from a point source derived by Airborne DOAS Tomography Participating scientists Irene Pundt, Klaus-Peter Heue, Bing-Chao Song Abstract First airborne DOAS tomography measurements of two-dimensional concentration crosssections of a plume from a point source have been carried out. The measurements were performed with an AMAXDOAS (Airborne Multi-AXis Differential Optical Absorption Spectroscopy) instrument onboard a small aircraft during the second campaign of the European FORMAT project in August / September 2003. Figure 2.32: Left: Lines of sight of the flight track as function of the geographic position of the Sermide power plant plume. X is the latitudinal, y the longitudinal and z the vertical direction. For clearness, only the downward looking viewing directions are shown neglecting the scattering of light. The colors of the lines indicate the NO2 slant column densities along each of them. Right: NO2 2D mixing ratio distributions of the Sermide plume after tomographic inversion, first pass (distance from the plant: 5 km). Background The focus of this study is the first application of the Airborne DOAS Tomography technique to provide concentration distributions of NO2 along cross sections of a plume from a point source. A technique to formulate a two dimensional inversion problem with weighting matrices from single scattering radiative transfer simulations, which can be used for tomographic inversions, is presented. Funding TomDOAS (BMBF), FORMAT (EU) Methods and results As part of the second campaign of the European FORMAT project (FORMAldehyde as a tracer of photo oxidation in the Troposphere), the instrument was installed on board a Partenavia PA 68 aircraft. During one occasion, on 26 September 2003, it was possible to derive the information for two-dimensional reconstructions of an emission plume of a point source. Three over flights were performed across the emission plume of the NO2 emitting Sermide power plant, located at 45.02 degree N 11.25 degree E. Three reconstructions have been performed, one for each overpass. It is assumed that the plume has not changed during the course of the measurement. Therefore 5, 6 and 9 aircraft positions, resulting in 50, 60 and 90 lines of sight were included for the 1st, 2nd and 3rd overpass, respectively (left figure). For each overpass, the area of interest is divided into rectangular boxes with 16 vertical segments of 133 m height and horizontal segments of 1.5 km length. For each inversion, the weighting matrix was calculated for the respective 2D grid. Then the inversion is performed using the Simultaneous Iterative Reconstruction Technique (SIRT) method. The right Figure presents the resulting NO2 mixing ratio maps for the first overpass. Interestingly the first and the third overpass, which were conducted very close by, show similar shapes, indicating only small changes of the plume during the 12 minutes flight interval. From this finding we conclude that the quality of the reconstruction is reproducible and consistent. NOX emissions of 4.1-9.6 10 24 molec s −1 were derived, in agreement with the information given by the power plant company. Outlook/Future work The analysis of the FORMAT flights is ongoing. Main publication Pundt et al. [2005a], Heue [2005]
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Institut für Umweltphysik und Arbe
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Contents 1 Introduction/Overview of
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CONTENTS 7 3.2.1 Glaciological pilo
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