An apparatus (100,200) for the removal of nitrous oxide in a gas stream (101,201) containing nitrous oxide which is derived from exhalation air and present in the gas stream in a concentration supporting exothermic decomposition of nitrous oxide. The apparatus has a main flow line (102,202) with: a) an inlet arrangement (103,203) with an inlet port (105,205), b) an outlet arrangement (104,204) with an outlet port (106,206), and between these arrangements c) a decomposition chamber (107,207). The main characteristic feature is that the decomposition chamber contains a catalyst material (108,208) promoting the decomposition of nitrous oxide to N2 and O2 together with a heat neutralizing medium (109,209).
