scope:

Scope and objective

This VDI-guideline is not intended to be applicationspecific but it can serve as a component for such a guideline. Calculation methods for atmospheric turbulence parameters supported by measurement values are presented which have to be available as input data for the application of different types of dispersion models. Through the given equations, the turbulence structure of the atmosphere is described by continuous stability variables (Section 2) on the basis of a meteorological pre-processors (Section 3) which is installed at the German Weather Service (Deutscher Wetterdienst - DWD) and which is operated with data from the synoptic stations of the DWD. This way, it is possible to now approach dispersion calculations, which were based so far on three-dimensional statistics of dispersion classes and were carried out with the Gaussian plume model, with more refined models using the same longstanding meteorological database. Turbulence structure may be calculated in dependence of stability and height as well as a function of surface roughness. This procedure is fundamentally different to the application of categorised dispersion parameters which have been derived from the scope of dispersion experiments at the Forschungszentren in Jülich and Karlsruhe for fixed emission heights and discontinuous stability ranges of the atmosphere. These parameters have been integrated in various technical guidelines of the Federal Republic of Germany.

The theoretical concept on which the previously described approaches are based, depends on isotropic and homogenous turbulence states. This idealised turbulence structure is only approximately realised even over flat and homogeneously structured terrain. Accordingly, the meteorological situation within the test area needs to be as "homogeneous" as possible e. if mesoscale circulation systems such as moun angegetain and valley breezes, land and sea breezes or frontal systems are present, the approach cannot be used.

The effect of veering of wind with height on turbulence and wind fields is not included in the presented parameterisation. Thus, the parameterisation can, strictly speaking, only be applied to dispersion calculations with source heights below 200 m and where the distance from the source is less than 20 km. The test area is limited to this space range. The mean wind velocity (referred to a height of 10 m above the disturbance level) in the test area may not decrease below 1 m/s. The parameterisation is unsuitable for the description of atmospheric turbulence and its related model-specific parameters for short emission times (e.g. explosive emissions). The quoted equations are more applicable if emissions, which occur over a time range of approximately half an hour, have to be depicted in a model. Using a series of more or less stationary situations, longer emission times may be considered.

Within this guideline, it is not intended to list methods for the description of turbulence which are based on the results of wind field models or those that may be used for turbulence parameterisation in such types of models. Specifications of this kind are still part of current research efforts and as such are not suitable for integration in technical guidelines.

Selection criteria for the recommendations of turbulence parameterisation stated in Section 4 are: consistency with the similarity theory, the possibility of a consistent formulation for all types of dispersion models within the framework of the Commission on Air Pollution Prevention of VDI and DIN - Standards committee (KRdL) and a steady transition between different turbulence states. The given equations are to be considered as the minimum requirement for parameterisations based on the similarity theory. However, deviations from these parameterisations are possible within the framework of the scattering width of the defined key variables. Selected stability areas of the atmosphere are depicted in a possible form as a function of height in Section 5 based on the recommended formulations for turbulence within the atmospheric boundary layer as stated in Section 4. Deviations which may occur due to the differences between experimentally determined measurement concentrations and calculated concentration values based on the given equations, are presented in Section 6.