A measuring system with a measuring system inlet and a measuring system outlet for investigating concentrated, larger aerosol particles of an aerosol in the gas phase, comprising a multi-stage aerosol particle concentrator for separating fine particles and a portion of the gas phase of the aerosol, as well as a measuring chamber for analysing the larger aerosol particles, wherein: i) the measuring chamber comprises at least one measuring instrument for the qualitative and/or quantitative determination of the aerosol particles, in particular in real time, and ii) the aerosol particle concentrator comprises a first and at least one last (4-x) virtual impactor stage each with a sample inlet, side outlet and sample outlet, wherein the virtual impactor stages separate a larger portion of the aerosol with fine particles and concentrate the larger aerosol particles in the smaller portion of the aerosol, wherein the aerosol particle concentrator - comprises an aerosol suction pump with an aerosol inlet and aerosol outlet for generating a negative pressure in the virtual impactor stages, wherein the side outlet of the first virtual impactor stage is connected to the aerosol inlet of the aerosol suction pump, characterized in that the aerosol particle concentrator comprises - a circulating flow channel in which a portion of the separated aerosol with fine particles is returned in the circulating flow from the aerosol outlet to the aerosol inlet of the aerosol suction pump, wherein the side outlet of the last (4-x) virtual impactor stage is connected to the circulating flow channel. i) the measuring chamber comprises at least one measuring instrument for the qualitative and/or quantitative determination of the aerosol particles, in particular in real time, and ii) the aerosol particle concentrator comprises a first and at least one last (4-x) virtual impactor stage each with a sample inlet, side outlet and sample outlet, wherein the virtual impactor stages separate a larger portion of the aerosol with fine particles and concentrate the larger aerosol particles in the smaller portion of the aerosol, wherein the aerosol particle concentrator - comprises an aerosol suction pump with an aerosol inlet and aerosol outlet for generating a negative pressure in the virtual impactor stages, wherein the side outlet of the first virtual impactor stage is connected to the aerosol inlet of the aerosol suction pump, characterized in that the aerosol particle concentrator comprises - a circulating flow channel in which a portion of the separated aerosol with fine particles is returned in the circulating flow from the aerosol outlet to the aerosol inlet of the aerosol suction pump, wherein the side outlet of the last (4-x) virtual impactor stage is connected to the circulating flow channel. - comprises an aerosol suction pump with an aerosol inlet and aerosol outlet for generating a negative pressure in the virtual impactor stages, wherein the side outlet of the first virtual impactor stage is connected to the aerosol inlet of the aerosol suction pump, characterized in that the aerosol particle concentrator comprises - a circulating flow channel in which a portion of the separated aerosol with fine particles is returned in the circulating flow from the aerosol outlet to the aerosol inlet of the aerosol suction pump, wherein the side outlet of the last (4-x) virtual impactor stage is connected to the circulating flow channel.