This International Standard specifies a standard reference method for the determination of PM10 and PM2,5 mass concentrations at stationary emission sources by use of two-stage virtual impactors. The measurement method is especially suitable for in-stack measurements of particle mass concentrations in flue gas. The method can also be used for flue gas which contains highly reactive compounds (e.g. sulfur, chlorine, nitric acid) at high temperature or in the presence of high humidity. The International Standard is applicable to higher dust concentrations. Coarse particles are separated into the nozzles with negligible rebound and entrainment phenomena of collected coarse particulates. For the same reason, the artefacts due to high concentrations in gases or emissions are quite limited. This International Standard is not applicable to the determination of the total mass concentration of dust.