This European Standard specifies the use of different metrics for the measurement of exposure by inhalation of NOAA during a basic assessment and a comprehensive assessment, respectively, as described in EN 17058 . This document demonstrates the implications of choice of particle metric to express the exposure by inhalation to airborne NOAA, e.g. released from nanomaterials1 and present the principles of operation, advantages and disadvantages of various techniques that measure the different aerosol metrics. Potential problems and limitations are described and need to be addressed when occupational exposure limit values might be adopted in the future and compliance measurements will be carried out. Specific information is mainly given for the following metrics/measurement techniques: - Number/Condensation Particle Counters by optical detection; - Number size distribution/differential mobility analysing systems by electrical mobility; - Surface area/electrical charge on available particle surface; - Mass/chemical analyses (e.g. Inductively Coupled Plasma atomic Mass Spectrometry (ICP-MS), X-Ray Fluorescence (XRF)) on size-selective samples (e.g. by impaction or diffusion). This document is intended for those responsible for selecting measurement methods for occupational exposure to airborne NOAA.