This book is concerned with the study of the pollutant dispersion emitted from a point source with changes of the wind direction within urban area under different conditions of atmospheric stability. It is experimentally investigated in a wind tunnel and full-scale field experiments. In addition, it is examined using theoretical dispersion model. Wind tunnel experiment was examined using Laser Doppler Velocimetry (LDV), Thermister Anemometer, Multi-Channel Anemometer, Thermocouples and a Hydrocarbon Analyzer Detector with a scanivalve. Full-scale field experiment was conducted using Ultrasonic Anemometer, Photo-acoustic Multi-Gas Monitor and Data Logger. On the other hand, a simple theoretical dispersion model is created and applied based on Gaussian Dispersion Model.