The method specified is based on drawing continuously, at a constant flow rate, an air sample through a particle filter before it enters the chemiluminescence analyser. It then flows into a reaction chamber where it is mixed with an excess flow of ethylene. Ozone and ethylene react instantaneously to produce light in the visible region (maximum at about 400 nm). The emitted light intensity is proportional to the concentration of ozone in the air sample and is measured by a photomultiplier tube. Applies to determination of the mass concentration of ozone between 2 µg/m^3 and 10 mg/m^3 at the reference conditions.