Plume rise and dispersion near the shoreline of a large lake when flow patterns are dominated by the lakebreeze

The rise and dispersion rates of the plume from a large thermal generating station located on the Lake Ontario shoreline in relatively flat terrain on the outskirts of a large city are examined under conditions where the local flow patterns are dominated by lake breeze circulations. For the periods of analysis winds aloft were observed using pilot balloons released over the land near the source and temperature structure in the vertical was observed on both sides of the shoreline using an instrumented light aircraft. This study was conducted with the full co-operation of the power company concerned and the characteristics of the emissions were readily available for the period of analysis. The plume was recorded for subsequent analysis using time lapse photographic techniques. Application of special films and filtering devices permitted observations to be extended beyond the point where the plume is no longer visible to the naked eye. Analysis of individual photographs is conducted using a photo densitometer to avoid error through the introduction of subjective interpretations. The position of the plume centerline in space and the vertical spread of the plume have been determined under conditions of moderate wind shear in the vertical and a slightly stable lapse rate through the layer of rise and dispersion. Tall stacks are used at the particular station observed and plume rise is enhanced by relatively large momentum and buoyancy forces. It is found that well above the surface) despite a strongly buoyant emission) within the lake breeze circulation system rise and rate of dispersion of a plume in the vertical are less than would normally be predicted on the basis of ground level observation of meteorological parameters. (author)