Reliable measurements of the sublimation rate of nonuniform layers of trinitrotoluene (TNT) microcrystals were carried out using a quartz crystal microbalance (QCM). The sample layer was prepared by precipitation of TNT from a well-defined volume of its solution in acetonitrile. The TNT solution was placed on the QCM electrode surface to form the precipitated layer of TNT microcrystals. It is shown that the kinetics of small TNT particles sublimation is controlled by the molecular diffusion in air. The sublimation process is well described by simple diffusion expressions that are discussed in the literature for both individual hemispherical-shaped microcrystals and disk-shaped layers. Expressions describing particle size evolution in time were derived based on this diffusion model. It is shown that the expressions developed can be used to simulate particle sublimation in a wide size range, including very small sub-micrometer particles.