The present invention relates to a measuring system for investigating concentrated, larger aerosol particles of an aerosol in the gas phase, having a multi-stage aerosol particle concentrator and also a measuring chamber for analyzing the larger aerosol particles, with at least one measuring device for the qualitative and/or quantitative determination of the aerosol particles, in particular in real time. The aerosol particle concentrator separates a larger part of the aerosol with fine particles and concentrate the larger aerosol particles in the smaller part of the aerosol. The aerosol particle concentrator includes an aerosol suction pump generating a negative pressure in the virtual impactor stages and a circulating-flow channel in which a part 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. The present invention also relates to a method for investigating concentrated, larger aerosol particles of an aerosol.