Australian Journal of Basic and Applied Sciences, 3(2): 486-496, 2009 ISSN 1991-8178 Characteristics of Concentration Pollutant in Plume Dispersal: Probability Study Mohamed F. Yassin and Abdirashid A. Elmi 1,2 2 Department of Environmental Technology and Management, College for Women, Kuwait 1 University, P.O. Box 5969, Kuwait, Safat 13060, Kuwait, Faculty of Engineering, Assiut University, Assiut-71516, Egypt. 2 Abstract: The instantaneous concentration fluctuation in pollutant plume dispersion in a neutral stratified atmospheric boundary layer previously measured experimentally in a wind tunnel experiment were used for the purpose of evaluating the probability of concentration distributions. The diffusion fields in the boundary layer were studied using an isolated building model. Instantaneous concentration fluctuations reported were measured along the mean plume centerline at various downwind distances from the source at different heights with the frequency of 1KHz. Probabilistic analysis was performed on the concentration fluctuation, and the probability density functions (PDF) of mean concentration, fluctuation intensity and crosswind mean-plume dispersion were developed. Furthermore, the effects of turbulence intensity on the statistical nature of concentration fluctuations were presented and discussed. Probability density functions of the concentration fluctuation data have shown a significant non-Gaussian behavior. The lognormal distribution appeared to be the best fit to the shape of probability density functions of fluctuating concentration measured in the boundary layer in the wind tunnel. It is also shown that the plume dispersion PDF near the source was shorter than that those far from the source. Keywords: Atmospheric dispersion; Concentration fluctuation; Probability distribution; Wind tunnel INTRODUCTION The boundary layer of the atmosphere is characterized by relatively high turbulence, with fluctuations in one-second averages of variables such as wind speed typically having magnitudes roughly equal to 10 to 100% of the mean value. When pollutants are emitted into this boundary-layer velocity field, they are carried out by turbulent eddies and also are observed to exhibit fluctuations at the same order of magnitude as their mean value. Therefore, these fluctuations are of great practical importance when the pollutant is highly toxic or flammable material. Most dispersion models are capable of predicting the mean pollutant concentration, but provide no guidance on the probability of fluctuations from this mean value (Hanna and Insley, 1989). The study of concentration fluctuations in dispersing plumes of pollutants in urban environment has resulted considerable advance in understanding the detailed structure of plumes in recent years. An understanding of concentration fluctuation is important for a number of practical applications. Several experiments have described tracer experiments using fast response concentration detectors. Those studies describe the turbulent fluctuations of concentrations at fixed points downstream of continuously emitting source. The results have given statistical descriptions of the concentration fluctuations under relatively simple atmospheric conditions in terms of, the standard deviation of concentration and the concentration probability density function (PDF). Study of probability distribution of fluctuating concentration has been hampered by a lack of suitable instrumentation. Some of the initial attempts at both predicting and measuring concentration fluctuations in ground level plumes have again emphasized the need for thorough experimentation. Recently, several studies have been completed for the probability distribution of concentration fluctuations. Sykes (1984), Hanna (1984), Sawford et al. (1985), Sawford (1987). and Diner et al. (1988). have agreed that the distribution of concentration fluctuation is skewed towards higher values, but disagree on the exact form of optimum distribution function. Furthermore, they have suggested analytical expressions for the mean and Corresponding Author: Mohamed F. Yassin, Department of Environmental Technology and Management, College for Women, Kuwait University, P.O. Box 5969, Kuwait, Safat 13060, Kuwait. E-mail: Mohamed_f_yassin@hotmail.com, 486