Abstract: A method and apparatus for determining a concentration of aerosol particles in a carrier gas. The method comprises providing an aerosol having aerosol particles in a carrier gas comprising at least one condensable component; introducing at least part of the aerosol into a chamber of a pressure-rated vessel, wherein the chamber is delimited by at least one wall adjoining the chamber and set to a temperature which is above a saturation temperature of the at least one condensable component; subsequently removing part of the aerosol from the chamber, as a result of which a decrease in pressure in the chamber occurs, as a result of which the at least one condensable component condenses at least partly on the aerosol particles; and determining a concentration of aerosol particles in the carrier gas during removal of the part of the aerosol from the chamber.