Use of INAA, PIXE and XRF in Homogeneity Testing of New IAEA Reference Air Filters

About 250 sets of polycarbonate (Nuclepore, Costar) membrane filters loaded with two urban air particulate matter (APM) obtained in Vienna and Prague were prepared by filtration of a watter suspension of the above APM materials. The homogeneity of both bulk APM materials and the loaded filters was tested by determining a number of elements by instrumental neutron activation analysis (INAA), proton induced X-ray emission (PIXE) and micro-X-ray fluorescence (-XRF). Relative standard deviations due to inhomogeneity (s_inh) were below 3% for many elements in the bulk APM materials. In the loaded filters, the s_inh values increased significantly. Nevertheless, for up to 20 elements important in air pollution studies the s_inh values were below 15%, allowing target values with a reasonably low uncertainties (up to 20%) to be derived for the future use of the filters in proficiency testing of laboratories involved in air pollution monitoring.