Validation of passive diffusion samplers for SO2 and NO2

Abstract Passive diffusion samplers of the type described by Ferm (1991) were tested at sites in Australia for measurement of ambient levels of SO 2 and NO 2 . For samplers exposed over periods of one to four weeks the passive diffusion samplers were found to provide quantitative measurements of these gases. Precision of the samplers, expressed as mean percentage difference between duplicates, was in the range 5–10% for NO 2 at ∼15 ppbv and 25–10% for SO 2 in the range 0.5–5 ppbv. Experiments with passive NO 2 samplers of different lengths confirmed the prediction by Heal and Cape ( Atmospheric Environment 31 , 1911–1923) of a significant artefact due to chemical reactions within the sampler, but also confirmed that the short tube length employed by the Ferm-type sampler renders this artefact insignificant for these samplers.