During three field campaigns at the Jungfraujoch High Alpine Research Station, Switzerland, size-fractionated aerosol was collected using a cascade impactor. The particles were impacted on silicon oil-coated quartz sampling substrates. The actual analysis was then performed directly on these quartz sampling substrates using total reflection X-ray fluorescence. The resulting size distributions of 16 elements (S, Cl, K, Ca, Ti, Mn, Fe, Cu, Zn, Se, Br, Rb, Sr, Y, Zr, Pb) were investigated to determine the best cut-off diameter to distinguish between geogenic and anthropogenic particles. The obtained cut-off diameter of 1 μm is an important parameter in the current world-wide measurements under the auspices of the World Meteorological Organization's Global Atmosphere Watch aerosol project.