From considerations of dimensional analysis, the relationship among particulate mass flow rate, wind speed, air density, and gravitational acceleration is a mathematical function in which the mass flow rate is proportional to the wind speed cubed. On the other hand, experimental and field observations to date have been presented as relationships in which entrainment rate is proportional to the n('th) power of the wind speed (the empirical values of n have varied between 1 to 9). An experimental investigation has been conducted at Iowa State University in the open circuit wind tunnel of the Aerospace Engineering Department. The entrainment rates of lycopodium spores, diffused from line or point sources have been determined for various ranges of wind speed. A functional relationship is presented in which the source strength is proportional to the cube of the wind speed times an exponential function of friction to threshold speed ratio. The application of this relationship to the present, as well as other experimental and field data, shows good agreement with results. Further, ground concentration diagrams are obtained due to point or line source diffusion of lycopodium spores. The effects of two and three-dimensional obstructions on the redistribution of concentration have been studied. The experimental results in the absence of obstacles are compared to numerical predictions. Finally, the results are compared with the available experimental and field data.