Fachdokumente Online der Landesanstalt für Umwelt Baden-Württemberg

zur LUBW   zum Ministerium für Umwelt, Klima und Energiewirtschaft   zum Ministerium für Ländlichen Raum und Verbraucherschutz   zum Ministerium für Verkehr und Infrastruktur  

Abstract

Close to the sources, aerosol properties are undergoing rapid changes. By a novel approach, the physical and chemical aerosol properties are determined by means of spatially and temporally highresolution lidar measurements in combination with numerical simulations of aerosol optical properties with a high-resolution microphysics-chemistry-transport model.

During a field campaign performed near a pig livestock farm in Mettingen, Westphalia, from 11.09.21.09.2005 data for this novel approach were collected. Lidar measurements and aerosol in-situ measurements were performed on 8 and 6 days, respectively. In the campaign a new mobile eye-safe 3dimensional-scanning lidar which was developed within this project was employed for its first time in the field. The investigated aerosol source was weak, i.e., not visible with the eye; it caused an increase of the aerosol number density down-wind of up to 5 % in the lowermost 50 m of the atmosphere. The primary particulate matter emission flux was estimated to be 100-500 g/h.

The measured data as well as the model prediction agree that the aerosol plume is localized quite low in heights below 50 m above ground. Because it was not yet possible to visualize the lidar data in realtime during the campaign nor to analyse the aerosol in-situ data in realtime which – furthermore - were only collected on the ground, the location of the aerosol plume was known only in the horizontal plane but not in the vertical. Thus, most lidar measurements were made at higher elevation.

On September 20, 2005, the aerosol plume was detected with the lidar. the 2-dimensional structure of an aerosol plume of a livestock farm and its temporal variability could be investigated and the particle backscatter coefficient of the aerosols could be measured, to our best knowledge, for the first time. The high-resolution lidar data (0.33 s and 30 m) reveal the aerosol transported by the wind and bending of the plume by turbulence. High resolution is essential, to study aerosol emissions in complex orography and under quickly changing meteorological conditions. Longer averaging shows a Gaussian-shaped aerosol plume. As for this day no in-situ aerosol data are available to initialize the model, the lidar measurements and model results cannot be compared directly. Instead, simulations were made to assess the upper and lower limit of the expected lidar data. The results agree in backscatter coefficient and shape of the plume with the measurements.

In the meantime, the lidar has been further developed. Now, the particale backscatter data are visualized in real-time which allows to see the structure of aerosol plumes and identify their source in realtime during the measurements. The implementation of rotational Raman lidar channels allows now the direct and simultaneous measurement of the particle backscatter and extinction coefficients. Furthermore, other important atmospheric parameters like temperature are measured simultaneously. These characteristics render the new lidar unique worldwide.

The model which has been developed within this project allows calculating the spatial structures of aerosols and their optical properties. A sensitivity analysis to quantify the uncertainties of the model results caused by incomplete knowledge of aerosol contents and mass concentration distribution shows that the particle backscatter coefficient can be assessed here only within +50/-70%. This uncertainty can be reduced in future field experiments by improved in-situ and lidar measurements.

The combination of observations and modelling developed within this project could be used for an improved representation of aerosol sources in large-scale atmospheric modelling. Furthermore, aerosol sources could be assessed with regard to the health hazards they possibly pose, a prerequisite for mitigation measures.

 


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