Aerosol optical depth (AOD) data from the Aerosol Robotic Network (AERONET) instrument at Goddard Space Flight Center were compared with surface chemical data from the Interagency Monitoring of Protected Visual Environments (IMPROVE) sampler at Washington, D.C. for the years 1995--1997. These sites were the only ones in the two networks in close enough proximity to make such a comparison. The Spearman correlation coefficients between AOD and boundary-layer aerosol properties derived from the IMPROVE data ranged from about 0.42 to 0.55. The relatively weak correlations for these urban sites are consistent with findings in previous studies, and are most likely due to the lack of information on the vertical profiles of aerosol mass concentration, composition, and relative humidity.