A water-soluble fluorescent-dye aerosol has been used successfully as a meteorological tracer. Because of simple instrumental analysis of field samples and great sensitivity, the technique offers large savings in the cost of tracer studies. The aerosol consists of 2- to 10-micron particles of uranine, generated by pneumatic atomization of a solution. The analysis is based on the fluorescence of a uranine-water solution. The sensitivity of the analysis is 10−10 g (corresponding to a single 5-micron particle) and samples as small as 10−9 g have been analyzed readily. The technique has been applied to a field program involving evaluation over distances up to 8 miles during periods of maximum atmospheric diffusion.