The activity median aerodynamic diameters (AMADs) of long-lived radon decay product ((210)Pb, (210)Po) in aerosols collected in the Barcelona area (Northeast Spain) during the period from April 2006 to February 2008 are presented. The (210)Po mean AMAD was 420 nm, while the (210)Pb mean AMAD was 500 nm. The temporal evolution of (210)Pb and (210)Po AMADs shows maxima in autumn and winter and minima in spring and summer. (210)Pb AMAD are being used to estimate the mean-residence time of atmospheric aerosols.