Development and validation of tools for the implementation of european air quality policy in Germany (Project VALIUM)
In the framework of the German Atmospheric Research Program AFO-2000 a system of consistent coupled numerical models has been developed. The purpose of the model system is to serve as a tool for the execution of European urban air quality regulations. A consortium with the acronym VALIUM was formed, which consisted of German research institutes, environmental consultancies and an environmental agency. A substantial part of the VALIUM program was devoted to the generation of a set of high quality data for the validation of the numerical model system. The validation data are based on a combination of field studies, tracer experiments and corresponding wind tunnel experiments. The field experiments were carried out inside and around a street canyon in a city district of Hanover/Germany. After a brief introduction to the VALIUM project a summary of the main results will be given.
Coupling of urban street canyon and backyard particle concentrations
Differences in particle mass and number concentrations between a busy urban street canyon (north-south orientation, about 50,000 vehicles 24 h -1 ) and an adjacent backyard were measured with optical particle counters. The influence of meteorological quantities, especially turbulent flow within the urban canopy layer, was also studied. Particle mass concentrations PM 10 and PM 1 were consistently larger within the street canyon due to enhanced emission and resuspension. For the study period this resulted in higher concentrations in the canyon of on average 30 % (PM 10 ) and 22 % (PM 1 ). Although elevated transport of submicrometer particles was related to easterly wind directions, the largest relative concentration differences between both sites were associated to cross-canyon flow from westerly wind directions. This is due to the canyon vortex being able to direct polluted air masses to the measurement site during flow being directed perpendicular to the canyon axis. For less polluted air within the backyard the backyard vortex is of minor influence. We found different influence of thermal and mechanical turbulence on the temporal evolution of concentration differences at both sites. Thermal turbulence was positively correlated with particle concentrations, while the latter was characterised by negative correlation coefficients.
Long-Term Sodar Observations in Moscow and a New Approach to Potential Mixing Determination by Radiosonde Data
The experimental data about thermal stratification of a low layer of atmosphere, received by the sodar sounding and direct measurements simultaneously, are summarized and discussed. The conclusion was made that sodar records of small-scale turbulent structures can be efficiently explained in terms of a thermal stratification type. The statistics of the thermal stratification in the lowest 800-m air layer are presented by the data of long-term sodar observations during 10 years at Moscow University, which were analyzed separately per hour. According to these data, the climatology of inversions, thermal convection, and weak-stable stratification is described. The mixing layer height, estimated by margins of turbulent structures on sodar records, was analyzed and compared with the one derived by traditional Holzworth method using radiosonde measurements. Climatology of the mixing-layer height in Moscow by the sodar data, as well as its variations due to synoptic effects, is discussed. A new approach is the usage of integral parameters (e.g., the instability energy) instead of heights to determine the potential mixing more precisely. This method allows us to eliminate errors of the height determination, when the temperature profile and dry-adiabatic line are close to each other. Moreover, instability energy in any case represents more realistic estimations of mixing because inertial lifting was taken into account.