A pollution estimation system (100) for estimating pollution level caused by exhaust gas of motor vehicles is provided. The system comprises an acoustic sensor interface (110) arranged to obtain use-data from an acoustic sensor comprising an audio sample of a motor vehicle sound and a trained exhaust gas model unit (120) arranged to receive as input the audio sample of the use-data and to apply a trained exhaust gas model to the received audio sample to produce an estimated pollution level associated with the received audio sample. The trained exhaust gas model has been obtained by training an exhaust gas model on multiple training items using a machine learning algorithm, the multiple training items comprising multiple audio samples of motor vehicle sounds obtained from one or more acoustic sensors and associated pollution levels.