Tracer Release Experiment

The tracer experiment concentrated on near-source dispersion with 10 sample sites located downwind within approx. two blocks of the release site. Planning for the release utilised both wind tunnel (EnFlo, Surrey) and numerical model (Cambridge) estimates.

The release was undertaken at 5:00pm on 15th May 2003 from a vehicle parked in York Street using two tracers: SF6 and the perfluorocarbon PMCH. Both were released for 15 minutes each, offset by 1.5 minutes. At the sampling stations, 10 consecutive 3 minute air bag samples were collected. All but one of the sampling stations were at ground level, the other being on the roof of WCC.

Moderate SSW winds prevailed throughout the release as a cold front approached. Initial results from the tracer release confirm the success of the experiment, with the tracers present in the air samples collected. There is in general a common pattern in the variation of concentrations of the tracer sampled at each site through time. Variations in the concentration levels were within the expected levels for the 3 minute sampling based on wind tunnel estimations deduced from block-averaged, higher sampling frequency data.