This International Standard specifies a method for sampling, sample conditioning and determination of dinitrogen monoxide (N2O) content in the flue gas emitted from ducts and stacks to atmosphere. It sets out the non-dispersive infrared (NDIR) analytical technique, including the sampling system and sample gas conditioning system. This International Standard is a reference method for periodic monitoring and for calibration, adjustment or control of automatic monitoring systems permanently installed on a stack. This reference method has been successfully tested on a sewage sludge incinerator where the N2O concentration in the flue gas was up to about 200 mg/m3.