The discussion about the particulate pollution of the air and its health effects is nowadays indispensable. But what makes particulate matter so dangerous? Basically, a distinction is made in the measurement between the two particle fractions PM10 and PM2.5. Under PM10 all particles fall with a maximum diameter of 10 μm, and with PM2.5 it is all particles, which diameter is smaller than 2.5 μm. With the naked eye, these particles are not visible. They are so small that PM2.5 particles in particular can penetrate into the alveoli. Even smaller particles of less than 1 μm in size are even able to penetrate into blood vessels.