Abstract: A condensation particle counter includes a saturation section, an aerosol inlet assigned to the saturation section, a condensation section, a measuring section for condensation particles, and an outlet section. The aerosol inlet allows a flow of an aerosol loaded with particles. Each of the condensation section, the measuring section and the outlet section are arranged downstream of the saturation section. A critical nozzle is arranged in the outlet section. The critical nozzle includes a critical nozzle inlet. A pump suctions the aerosol. An outlet line extends from the critical nozzle to the pump. A valve device is arranged in the outlet line between the critical nozzle and the pump. A pressure measuring device is arranged upstream of the critical nozzle inlet. The outlet line is entirely closed or partially closed by the valve device depending on a measurement value of the pressure measuring device.