The charges of airbome 3, 5 and 10 mu m spherical dielectric test particles passing through a novel AC unipolar charger have been measured individually. The measurements show the effectiveness of the charger and provide statistics on the particle charges measured. The 3 mu m particles were charged to significantly higher values than expected. These log-normally distributed particle charges were found to have an average significantly above the saturation level for dielectric particles. This is most probably because of increased surface conductivity due to sodium and chlorine surface impurities from dried surfactant used for the storage of such particles. (C) 2005 Elsevier Ltd. All rights reserved.