Abstract: A gas sensor 10 for detecting particles in a gas stream has a first electrochemical pump cell 14, which has a measuring chamber 16 in which a first electrode 18 is disposed to pump particles between the first measuring chamber 16 and the gas stream. Furthermore, a second electrochemical pump cell 20 is provided, which has a second measuring chamber 22 in which a second electrode 24 is disposed so as to pump particles. According to the invention, the second measuring chamber 22 is connected to the gas stream via an absorber medium 34 for absorption of the particles to be detected. This makes it possible to absorb the particles to be detected in a first operating mode using the absorber medium 34, and to desorb the absorbed particles in a second operating mode, and to detect the quantity of the desorbed particles. Thus, the gas sensor 10 is able to take even low concentrations into account, and short-term measuring errors do not have such a serious effect.