1 .l General This International Standard specifies a chemiluminescence method for the determination of the mass concentration of ozone in ambient air. The method is applicable to the determination of the mass concentration of ozone between 2 pg/m3 [O,OOl ppm(V/V)] and 10 mg/m3 [5 ppm(V/V)] at the reference conditions of 25 “C and 101,3 kPa. Ultraviolet (UV) photometry is specified as the primary calibration method because of its proven accuracy and specificity to ozone. The use of transfer Standards is allowed if they have been previously calibrated against the primary calibration method. 1.2 Limitations The chemiluminescent reaction of ozone with ethylene is not subject to interference from any of the common air pollutants. However, particulate matter, if not removed, will accumulate in the sampling line and may Cause a measurable destruction of ozone. If particulate matter is allowed to enter the reaction chamber of the analyser, it will not only scatter the emitted light but will also accumulate on the Optical window, thereby causing further attenuation of the emitted light. Also, any nitrogen(ll) Oxide in the sampled air will to some extent react with the ambient ozone; therefore, the time during which the ambient air remains in the sampling line must be sufficiently short to keep this effect to a minimum. NOTE 1 It has been reported by some researchers that, at about 80 % relative humidity and 22 “C, the responses for some commercially available chemiluminescence analysers were about 10 % higher than that for dry air. However, comparisons of ambient ozone measurements using commercially available chemiluminescence and UV-photometric analysers showed no significant differentes. This suggests that, in practice, any errors associated with calibrations using dry air are compensated by other effects.