As far as concerns the risks of nanotechnology, the focus of attention is on nanomaterials and in particular on free nanoparticles. Alongside the investigation of their possible toxicity, the question of the exposure of humans and the environment is an essential element of their risk assessment. Nanoparticles suspended (distributed and embedded) freely in the air are of particular relevance, since they can easily penetrate the human body via the lungs. In addition, it is extremely difficult to monitor the spread of nanoparticles in the air.
Commercially available particle counters can be used to determine the concentration of particles and droplets in the air down to a size of a few nanometres. In the light of the high background concentration of natural nanoparticles and those generated by human activity, the first priority is to distinguish between natural and synthetic nanoparticles. While an on-site concentration measurement can be carried out in a few minutes, the analysis of the nanoparticles contained in the air, that is the determination of their form and composition is only possible using complex electron microscopy procedures in the laboratory. This situation currently constitutes the main problem for determining the concentration of synthetic nanoparticles and will do so for the near future.