Ultra-fine particles make up only 10% of the mass, but 90% of air pollution. Nevertheless, they are not yet adequately taken into account in current legislation, which only addresses the mass of particles. Initially, via a limit value for PM10 (particles with a diameter of fewer than ten μm) and since 1.1.2010 additionally via a limit value for PM2.5 (particles with a diameter of fewer than 2.5 μm). Such particles can be measured in any authorized laboratory. Even particles of the size PM10 are not visible to the naked eye and are significantly smaller than a human hair (50 μm). The investigations of the Leibniz Institute for Tropospheric Research (TROPOS) (Fig. 2) show that the proportion of organic and elemental carbon (OC/EC) is particularly high in the ultrafine particle range.