A compact elastic lidar was built to measure depolarization ratios from bio-warfare agent (BWA) simulant and interferent aerosol cloud releases in a recent field test using a 523.5 nm laser. Strong depolarization ratios were obtained for several of the simulants, while the interferents such as diesel exhaust gave very low depolarization ratios. Measurements of depolarization together with laser induced fluorescence can improve discrimination between BWA and non hazardous aerosols and reduce false alarms. In a separate experiment, a 1,047 nm laser was used for the same simulant and observed different depolarization ratios as expected from the particle size distribution. The experimental results were compared with the T-matrix calculation of the depolarization ratio.