Abstract As a contribution to the joint research project FEBUKO, hygroscopic properties of atmospheric Aitken and accumulation mode particles were measured in the Thueringer Wald, Germany, using a hygroscopicity-tandem differential mobility analyser (H-TDMA). The hygroscopic growth of particles with initial dry diameters of D p = 50 , 150, and 250 nm at 90% relative humidity was used to calculate average distributions of the soluble volume fraction with respect to the hygroscopic growth of ammonium sulphate. The application of this parameterisation procedure was tested by analysing the dataset with respect to the dependence of the soluble volume fraction on particle size and air masses character. With increasing dry particle size, the fraction of particles containing high soluble volume fractions was found to increase. The number of accumulation mode particles in marine air masses passing the sampling site having a large soluble volume fraction was significantly higher than in air masses of more continental character. For particles with D p = 50 nm , no air mass dependence of the soluble volume fraction was found. In marine air masses, particles with D p = 150 and 250 nm are assumed to undergo similar evolution processes, whereas in continental air masses this seemed to be the case for particles with D p = 50 nm and 150 nm.