The performance of an aerodynamic lens operating at atmospheric pressure is analyzed numerically, and the results are verified through experiments measuring the particle beam size by laser light scattering. It is shown that a strongly focused particle beam is obtainable with a single orifice at atmospheric pressure, when the orifice Reynolds number is in the range 300 < Re < 700. Two different orifice sizes, d/D = 0.1 and 0.2, and particle sizes of 1-10 mum are studied with the Stokes number in the range 0.01 < St < 3.0. The smaller beam can be generated with the smaller orifice, but the concentration factors for different orifice sizes overlap giving a universal curve, when plotted versus Stokes number. Experimental results are in a very good agreement with numerical results. (C) 2003, Elsevier Science Ltd. All rights reserved.