The goal of this study was to determine under what conditions, if any, measurements of aerosol properties made at the Earth's surface are representative of the aerosol properties within the column of air above the surface. This project used data from the Atmospheric Radiation Measurement (ARM) site at the Southern Great Plains (SGP) site, which is one of the only locations in the world where ground-based and in situ airborne measurements of atmospheric aerosol are made on a routine basis. All flight legs in the one-year period from March 2000 to March 2001 were categorized as either within or above the atmospheric boundary layer (ABL) using an objective mixing-height-determination technique. The correlations between the aerosol properties measured at the surface and those measured within and above the ABL were then computed. The conclusion of this comparison is that the aerosol extensive and intensive properties measured at the surface are representative of values within the ABL, but not within the free atmosphere.