Dispersion measurements of a tracer, uranine dye in solution, were made out to two miles from the re- lease point in unstable atmospheres. The tracer was released from the top of a 150-ft tower and sampled at ground level by 100 high-volume air samplers. Some sixteen releases for 30-min periods were analyzed. Techniques of dispersal, collection and analysis of the tracer are included. Meteorological measurements during the tests included vertical- and horizontal-wind-direction fluctuations at several levels on the 150-ft tower and vertical temperature difference. Measured air concentrations agree well with those predicted from a meteorological model using wind- direction variances as dispersion parameters. Prediction equations are also empirically developed for computing the distance to maximum ground-level air concentration and for lateral particle variance to two miles. The measured vertical inhomogeneity of turbulence does not prevent a fair agreement between pre- dicted and measured surface a... Abstract Dispersion measurements of a tracer, uranine dye in solution, were made out to two miles from the re- lease point in unstable atmospheres. The tracer was released from the top of a 150-ft tower and sampled at ground level by 100 high-volume air samplers. Some sixteen releases for 30-min periods were analyzed. Techniques of dispersal, collection and analysis of the tracer are included. Meteorological measurements during the tests included vertical- and horizontal-wind-direction fluctuations at several levels on the 150-ft tower and vertical temperature difference. Measured air concentrations agree well with those predicted from a meteorological model using wind- direction variances as dispersion parameters. Prediction equations are also empirically developed for computing the distance to maximum ground-level air concentration and for lateral particle variance to two miles. The measured vertical inhomogeneity of turbulence does not prevent a fair agreement between pre- dicted and measured surface a...