An evaluation of Gaussian plume-depletion models with dual-tracer field measurements

Abstract

To evaluate atmospheric diffusion-deposition models, airborne tracer concentrations were measured during simultaneous releases of depositing (ZnS) and nondepositing (SF 6) tracers. The effective deposition velocity of the ZnS tracer, a polydisperse aerosol, was obtained from the near-surface, crosswind-integrated, dual tracer concentrations, using a method based on the surface depletion model of Horst (1977, Atmospheric Environment 11, 41–46.). These deposition velocities were in good agreement with predictions based on the particle size distribution of the ZnS tracer and on wind tunnel measurements of the deposition velocities of monodisperse aerosols. Four Gaussian plume-depletion models were evaluated with the dual tracer data. Source depletion and constant eddy-diffusivity models were found to overestimate the depositing/nondepositing concentration ratio near the surface, but the estimates of these models were noticeably improved by a profile correction to the source depletion model and a mass-conservation correction to the K model. Of the four models tested, the corrected source depletion model gave the best agreement with the observations.