Nanoparticles which float in the air may seem somewhat insignificant. Nevertheless, knowing them is a vital in many fields: for example, when evaluating individual or room filtration systems, the effectiveness of protection equipment for workers who handle potentially dangerous elements and the suitability of the handling practices of nanoparticles in industrial processes.

http://www.nanobasque.eu/aNBW/web/en/society/reports/index.jsp?nId=94