Validation of passive diffusion samplers for SO2 and NO2

Passive diffusion samplers of the type described by Ferm (1991) were tested at sites in Australia for measurement of ambient levels of SO2 and NO2. 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 NO2 at similar to 15 ppbv and 25-10% for SO2 in the range 0.5-5 ppbv. Experiments with passive NO2 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. (C) 1998 Elsevier Science Ltd. All rights reserved.