A portable system 1 for analyzing gaseous flows that vary over time is described, the system comprising a sampling chamber 18, a gas sampling module 7, an ion filtering module 8 and an ion detecting module 9. The gas sampling module 7 is configured to adjust an input gaseous flow Fi of gas particles from the sampling chamber 18, ionize said gas particles and to emit the produced ions, so as to generate an ion flow I. The ion filtering module 8 is configured to controllably select at least one type of ion present in the ion flow I and to generate a corresponding at least one homogeneous ion beam I′, having an intensity representative of the concentration of the corresponding gas particle in the gaseous composition to be analyzed. The ion detecting module 9 is configured to measure the intensity of the at least one ion beam I′.