This document covers the monitoring of air cleanliness by particles in terms of concentration of airborne nanoscale particles. For monitoring purposes, only populations of particles with a lower size limit of 0.1 microns (100 nm) or less – “nanoscale” – are considered. The monitoring given in this document is for use mainly in “operational” states. NOTE 1 For the purposes of this document, reference is made to “nanoscale particles”, which means all nano-objects having one (nanoplate), two (nanofibre) or three (nanoparticle) dimensions in the nanoscale. NOTE 2 As a consequence, the specifications for monitoring air cleanliness by nanoscale particle concentration of the cleanroom in operational state also considers process specifics, e.g., used equipment, personnel behaviour, etc. NOTE 3 Health and safety considerations are excluded from this document.