A LABORATORY STUDY AND IMPROVED PDF MODEL OF FUMIGATION INTO A GROWING CONVECTIVE BOUNDARY-LAYER

A saline convection tank was used to study the fumigation of a plume a s it is entrained into and rapidly mixed through a growing convective boundary layer. Dispersion results in the form of crosswind-integrated concentrations for the whole field were obtained using a quantitative video digitization technique. Good agreement was obtained with a prob ability density function (PDF) dispersion model when it was modified t o properly account for the spatial variability of the local mixed laye r height. A wide range of boundary layer growth rates from very slow ( 0.002w) to fast (0.15w*, where w* is the convective velocity) was inv estigated to determine the influence of growth rate on ground-level co ncentrations (GLCs), duration of the fumigation episode, and thickness of the boundary layer entrainment zone. Within this range of growth r ates, maximum crosswind-integrated GLCs were found to be only very wea kly dependent on the entrainment rate. The duration of a fumigation ep isode was found to be proportional to the sum of the entrainment zone thickness and the initial plume spread and inversely proportional to t he boundary layer growth rate. The experimental and model results are shown to be applicable to fumigation into a thermal internal boundary layer developing inland from a shoreline as well as to nocturnal inver sion breakup fumigation. Copyright (C) 1996 Elsevier Science Ltd