The dispersion of sulfur hexafluoride tracer and sulfate from automobile emissions in the immediate vicinity of a highway were estimated for conditions similar to those existing during the General Motors sulfate dispersion experiment conducted at a GM test track. A second-order closure model of turbulent transport in the planetary boundary layer was used to predict the steady-state dispersion under two conditions: with the mean wind and velocity component variances specified by the data or predicted with the aid of an automobile wake model. The GM measured wind data apparently suffered from low vertical velocity variance readings at the 1.5 meter height, and led to an overprediction of the SF6 levels by an average factor of 1.77 for the 18 tower collection points during the 15 test days. The correlation fell to 0.96 of the measured levels when the model also predicted the wind fields. The results indicate that close to the highway, buoyancy effects were small even in the critical case when the wind is light and aligned with the roadway.

"EPA-600/4-79-013." Prepared by Aeronautical Research Associates of Princeton, Inc., under contract 68-02-2285. "Project Officer Francis S. Binkowski." ""Feb. 1979. Includes bibliographical references.