Trace gas concentrations and atmospheric state parameters were measured aboard the NOAA King Air research aircraft during flights on August 16, 1988, along the Appalachian Mountains from central Pennsylvania to northern Georgia. Stepwise profiles were flown over five surface sites where measurements of certain atmospheric parameters were being made. A stationary cold front lying across southern Virginia effectively divided the area into two weather regimes; to the north of the frontal zone the air was slightly cooler and much drier than that to the south. Considerable convective activity developed from early to midafternoon along and south of the front. The comparison between the aircraft and ground sites included measurements of the primary pollutants SO2 and several hydrocarbons, NOy, the secondary pollutants H2O2 and O3, and meteorological parameters. Continuity between the aircraft and surface meteorological and trace gas measurements was consistent at the northernmost site, which is situated in a relatively level valley. The agreement was poorer at the other four ground sites, which are located on or near mountaintops. Most of the meteorological and trace gas measurements, other than those made at Scotia were found to differ by substantial margins, often by more than 10 times the resolution of the instruments. However, within a few hours after the flights, the surface measurements, particularly those of H2O2 and O3, achieved values comparable to those measured with the aircraft, thus suggesting that air sampled at the canopy level did not mix readily with the bulk of the boundary layer.