To the relevant diameter of aerosol particles in the 0.1 to 1 μM transition range.

Modern techniques used for particle sizing in the 0.1 to 1 μm transition range are based on different kinds of forces acting upon the particles. In a spiral centrifuge or a low pressure cascade impactor particles are exposed to mechanical forces and can be classified according to their aerodynamic diameter down to about 0.08 resp. 0.03 μm. In a differential mobility analyzer (DMA) particles are separated by electrical forces up to particle diameters of about 1 μm. Submicron particles below about 0.4 μm are often measured in diffusion batteries where particles are classified according to their diffusion coefficient. The diameter derived from the electrical mobility and from the diffusion coefficient can be combined to a common mobility diameter which is only a function of the geometrical particle dimensions. When studying particle behaviour in aerosol systems one has to be cautious in all cases where the forces acting upon the particles during the experiments differ from those ones used for their size characterization. To demonstrate this problem number size distributions of atmospheric aerosols are considered and particle deposition studies in human lungs are reported