An inlet conduit (32) connects to aerosol source (100) of an initial particle concentration. A first flow path having particle counter (62) connects to inlet conduit (32). A second flow path (36) connects to the inlet conduit (32) and branches to form third flow path (38) and fourth flow path (40) which meet at junction (50). A flow restrictor (42) is positioned in the third flow path (38). Filter (44) and a flow meter (46) are connected in the fourth flow path. An outlet path (52) connects to the junction (50). A low particle counter (54), a second filter (56) and a second flow meter (58) are positioned in the outlet path. The system can accurately perform a traceable measurement of the dilution factor of an aerosol particle concentration traceable to national standards and allows for traceable measurements of aerosol concentrations below the dynamic range of a given particle counter.