During limited-mixed convective conditions, high concentrations of air pollutants have been observed at ground-level from buoyant plumes. Routinely-applied Gaussian plume dispersion models have difficulty simulating diffusion for these conditions. However, advances in convective scaling offer some hope for improved model formulations. The paper evaluates the usefulness of a diffusion formula proposed by Briggs. Thirty-nine hours of extensive meteorological, source, and tracer data were analyzed from the Kincaid field study. The evaluation of the Briggs formula compared to a Gaussian plume dispersion model showed better model performance.