A new technique to measure spatial distributions of aerosols in rooms is presented. This measurement system is based on Particle Image Velocimetry (PIV), which has non-intrusive, simultaneous, and whole field measurement features. In this quantitative flow determination, tracer particles and surrogate aerosols are introduced into the indoor air, illuminated by a light sheet,and photographed. Image shifting is used to determine the direction of particle movement. The digital images are processed automatically by image interrogation techniques. The particle size, the concentration spatial distribution, and a two-dimensional velocity vector map can be obtained by applying different data analysis techniques and calibration procedures.