In this study we provide aerosol characteristics for two case-studies from a summertime campaign over the northern Mediterranean region. Airborne measurements over the northern Adriatic and the western coast of the Black Sea provide a vertically resolved picture of aerosol optical, microphysical and chemical properties, and the horizontal variability of pollution across eastern and western Europe. Observed variations in the characteristics can be principally attributed to the source region of each air mass. This is particularly evident in a stratified aerosol profile over the Black Sea that results from an eastern European air mass at low altitudes underlying an air mass originating from central and western Europe. The atmospheric column over the Adriatic was found to be more homogeneous, both optically and in composition, comprising western European industrial pollution. Analysis of the chemical components of the sampled aerosol showed that the elevated pollution layer over the Black Sea was dominated by sulphates, while the lower layer was dominated by organic compounds, most likely due to agricultural fire events that were visible from the aircraft. This difference in chemical composition was reflected in the in situ single-scattering albedo; the lower layer had a mean value of 0.91 while the elevated layer had a higher mean value of 0.95, indicative of a stronger scattering component. Measurements over the Adriatic Sea displayed more consistency in composition between the two layers and a less apparent difference in the single-scattering albedo (SSA; 0.89 and 0.90 for the lower and elevated pollution layers, respectively). Airborne observations are complemented by surface sunphotometer and lidar retrievals, and satellite retrievals where available, and a closure investigation is performed to examine consistency of optical properties between these datasets. Copyright (C) 2007 Royal Meteorological Society.