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.
Frequency distributions of the mixing height over an urban area from SODAR data
The height of the mixing-layer (MLH) is an important parameter in the assessment of the dilution of primarily emitted or secondarily formed air pollutants in the atmospheric boundary-layer. A continuous measurement of MLH is possible only by remote sensing. Here, 17 months of SODAR data have been analysed automatically to derive the MLH over the city of Hannover in Northern Germany. In contrast to earlier studies the MLH has been determined from vertical profiles of the acoustic backscatter intensity and from the variance of the vertical velocity component. The results are presented in form of monthly frequency distributions and mean daily courses of MLH. These statistical evaluations of MLH show a clear annual course and interannual variability. The study shows the possibility to derive meaningful climatological information from long-term SODAR measurements for air quality issues.
Seasonal mixing heights and inversions at Edmonton, Alberta
High-resolution temperature profile data collected by balloon-borne ascents from 1977 to 1983 were analysed to determine mixing heights and ground-based inversion depths. Early morning ground-based inversions occurred with a frequency ranging from 44% in spring to 88% in fall. Median depths of early morning ground-based inversions were found to range from 315 m in the spring to 414 m in the summer, fall and winter seasons, with median potential temperature gradients of 0.016, 0.021, 0.026 and 0.030°C m−1, respectively. Quartile deviations of ground-based inversion depths and strengths were about 30% of median values. Median mixing heights at solar noon in the spring, summer, fall and winter were 683, 659,381 and 162 m, respectively. The kink method gives consistently lower values of mixing heights than the Holzworth and capping methods for all seasons and times of day. Mixing heights determined from these data were generally lower than those estimated from rawinsonde data in earlier studies.