Which ultra-fine particle concentrations can we expect?

There is no standardization on ultra-fine particles at the moment. However, scientific discussions are ongoing on the formation of a standard. Nevertheless, it is possible to give some reference concentrations (Ultra-fine particles are measured in concentrations particles/cm3)

Clean air in the alps < 1.000
Clean office air 2.000 – 4.000
Outside Air in urban area 10.000 – 20.000
Polluted outside air (smog) > 50.000
Cigarette smoke > 50.000
Workplaces (like welding) 100.000 – 1.000.000


Note, it is expected that there is no threshold concentration below which there is no negative health effect. Air should be as clean as practically possible. The threshold concentration at which people feel immediate impact is around 50.000 particles/cm3. Asthmatic people immediately feel the effect of smog.

Surface area, particle number, and size
Traditionally, the concentration of airborne particles is often measured as a mass concentration. Other measurement units such as number concentration or surface area concentration (total surface area of all particles in a volume of air) have a much more significant relation to the health effects. The table below shows the number and surface area concentration of a cloud of particles with a total airborne mass concentration of 10 µg/m3 when it contains particles of different diameters and clearly shows the remarkable effect of the particle diameter. The number of particles in a certain volume of air increases dramatically along with the surface area per unit volume of air, as the particle size decreases into the region of ultra-fine particles.