Froin January 2006 on, a continuous experiment consisting in determinations of granulometrie composition of the airborne dust has been performed in the Institute of Environmental Engineering of PAS, Zabrze. The investigations include measurements of concentrations of PM1 - the suspended in ambient air particles of the aerodynamic diameter not grater than I μm - by using the PM10 Dekali impactor. The results of twelve month measurements (January - December 2006) arc presented in the paper: the granulometrie composition of total suspended dust (PM10, PM2.5, PM1) in winter and summer at an urban background site in the Silcsian Agglomeration. Monthly and seasonal average concentrations of PM I O, PM2.5 and PM1 were computed.