An instrumented tethered balloon, acoustic Sodar and micropulse LiDAR, and ground-based sensors were used to characterize the atmospheric boundary layer from the surface to 750 meters in support of the “Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ)” campaign during July 2011 in Edgewood, MD. The primary objective was to connect ground-based measurements with airborne measurements obtained by the NASA P3B aircraft during overpasses. The balloon profiles were a series of vertical ascents to maximum altitude followed by descents punctuated by time series at constant altitudes during P3B over-flights. Instruments carried on the tethered balloon documented the meteorological variables T, p, q, and wind velocity, chemical species (O3, NO, NO2, NOx), PM2.5 and CCN. The results are being integrated with measurements of other investigators to provide a detailed description of the evolving boundary layer. Preliminary results from selected case studies will be presented illustrating the importance of horizontal transport and stability on local air quality. Special emphasis is given to morning transition periods and regional bay/sea breezes and their influence on pre- and post-intrusion air quality.