Elevated Source SF₆-Tracer Dispersion Experiments in the Copenhagen Area

Atmosperic dispersion experiments were carried out in the Copenhagen area under neutral and unstable conditions in order to study the atmosperic dispersion process in a built-up area. The tracer sulphurhexafluoride was released without buoyancy from a tower at a height cf 115 m, and then
collected at ground-level positions in up to three crosswind series of tracer sampling units, positioned 2-6 km from the point of release.

A description is given of the developed tracer technique and the instrument system for the determination of the three-dimensional fluctuating wind velocity used in these experiments.

The dispersion parameters were estimated from the measured tracer concentration distribution and compared with the dispersion parameters that can be calculated from the measured atmospheric parameters by various standard methods. Some of these methods have been in common use for a long time, while others reflect the current stage of research. Theoretical aspects of the various methods are considered and discussed in the light of the experimental results. Based on the experinents, a semiempirical model is devised for predicting the lateral and vertical dispersion parameters for elevated point sources in an urban area under neutral and unstable conditions.

This report also contains a review of the fundamentals of dispersion theory. The more significant experimental campaigns reported in the literature are discussed briefly.