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 water suspension of the above APM material
s. The homogeneity of both bulk APM materials and the Loaded filters was te
sted by determining a number of elements by instrumental neutron activation
analysis (INAA), proton induced X-ray emission (PIXE) and micro-X-ray fluo
rescence (mu-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 t
o 20 elements important in air pollution studies the s(inh) values were bel
ow 15%, allowing target values with a reasonably low uncertainties (up to 2
0%) to be derived for the future use of the filters in proficiency testing
of laboratories involved in air pollution monitoring.