Abstract

The Meteorological Service of Canada has recently developed a mobile scanning lidar facility (RASCAL: Rapid Acquisition SCanning Aerosol Lidar) capable of fast azimuth and elevation scanning profiles of the lower troposphere. Lidar is a remote sensing technique that provides high temporal and spatial information on atmospheric particulates and was ideally suited for characterizing stack plume dynamics. RASCAL was located predominantly downwind of the Noranda-Horne smelter stack source located in northern Quebec. Two three-week periods during February (winter) and July/August (summer) of 2000 were chosen to examine the behaviour of the plume because of the differences in humidity and boundary layer dynamics. The scanning speeds were adjusted to allow a complete scanning profile to be collected within 30–60 seconds. Along-plume-axis and cross-sectional scans provided an opportunity to directly measure plume dynamics and interaction with the planetary boundary layer, including the ability to detect fumigation events. Several algorithms have been developed to quantify the area, shape, horizontal and vertical extents of the plume as a function of the distance from source. Examples are shown where the cross-sectional area of the plume remained constant at a given distance from source even though its shape was highly variable. Also, boundary layer height, wind speed and direction of the plume can be extracted from the RASCAL data under certain conditions. These data are valuable for comparison with model predictions as well as providing initialization input for long range dispersion models.

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