A method of nitrogen dioxide and sulphur dioxide determination in ambient air by use of passive samplers and ion chromatography

A passive sampling method for simultaneous determination of SO2 and NO2 in ambient air is presented. Sampling periods from 24 h to 1 month can be applied. SO2 and NO2 collected by the sampler are determined as sulphate and nitrite with ion chromatography in a single run. Both suppressed or nonsuppressed IC can be applied with the former giving lower detection limits. Analysis for NO2 as nitrite can be also performed spectrophotometrically after reaction with Saltzman reagent. The lower determination limit for monthly exposure of samplers is 0.5 and 0.7 μg m−3 for NO2 and SO2, respectively. For shorter periods of exposure the determination limit is proportionally higher. Precision of the method as RSD is 6% for NO2 and 14% for SO2 at concentrations of around 50 μg m−3. Influence of meteorological factors like sunlight, wind velocity, temperature and humidity of air on sampling rate have been minimised by an appropriate modification of the sampler and calibration of the method under various conditions. The method has been optimised to make it possible to perform large number of analyses at a very low cost. Passive samplers can be stored before and after exposure for a period of up to 10 weeks what makes it possible to prepare and analyse them by a central laboratory for better integrity of data. Samplers can be sent from and back to the central laboratory by mail. Suitability of the method for large-scale monitoring was demonstrated in several projects.