The influence of non-uniform Po-218 density distribution on the downstream filter was estimated on the basis of a numerical analysis of the aerosol particle transport inside a tube and of a numerical estimation of the efficiency for alpha radioactive particle detectors. For published diffusion coefficients of 0.103, 0.067 and 0.045 cm(2) s(-1), the error was found to be +20%, +25% and +26% respectively, compared with a uniform deposition.