Simulation of atmospheric diffusion in low windspeed meandering conditions by a Monte Carlo dispersion model

Abstract

Conditions of low windspeed associated to strong stability and air stagnation correspond to highly nonstationary and inhomogeneous diffusion situations. In such «poor» diffusion cases, integrated models (like Gaussian models) are no longer valid. New numerical methodologies, like Monte Carlo methods, are needed. Recently a Monte Carlo particle model for airborne pollutant dispersion has been developed by our team. Its ability to predict ground-level concentrations in convective and neutral conditions with a high degree of accuracy was verified against tracer experiments. In the present paper our model is used to simulate the dispersion under low windspeed conditions. Particular emphasis is given to the problem of wind meandering. We have demonstrated the need of recording the wind statistics over averaging periods of the order of a few minutes and anad hoc algorythm to treat low windspeed situation when only hourly average data are available is suggested. The model results are compared to tracer data obtained by the Idaho National Engineering Laboratory (U.S.A.) in 1974.