The work studies the influence of how the unattached fraction of radon daughters can influence effective dose. An experimental work was carried out for measuring the unattached fraction in presence of different size aerosols, and for each test an estimate of the effective dose was given. Tests were carried out at fixed radon concentrations and with different size aerosols. Potential alpha energy concentrations of both total and free fractions were measured, together with radon and aerosols air concentrations. Results showed increments of the equilibrium factor, reduction of the unattached fraction, and decrease of the effective dose. © 2017, Akadémiai Kiadó, Budapest, Hungary.