Airborne mass concentration (μg/m3) Particle diameter (μm) Particles/ml
of air
Particle surface area (μ3/ml air)
 1021.224
 100.5153120
 100.0224000003016

Table modified from data of G Oberdorster. The relevance of this lies in the fact that any monitor collecting all of these particles in these three different conditions would always give the same airborne mass concentration of 10 μg/m3. However, the physical characteristics of the cloud are very different for particle number and surface area and both of these are properties that might have important impact on the lung.