A passive sampler for SO2 and NO2
This method has been used in industrial areas, in urban areas and for studies of indoor/outdoor exposures.
A sensitive diffusion sampler for sulphur dioxide (SO2) and nitrogen dioxide (NO2) in ambient air has been used in several investigations to undertake a screening of the spatial concentration distribution.
The sampler was developed by the Swedish Environmental Research Institute (IVL) and has been used in several cases by NILU. The sampler includes an impregnated filter inside a small plastic tube. To avoid turbulent diffusion inside the sampler, the inlet is covered by a thin porous membrane filter. Gases are transported and collected by molecular diffusion. The uptake rate is only dependent upon the diffusion rate of the gas. The collection rate is 31 l/24h for SO2 and 36 l/24h for NO2. Also NH3 can be collected at a rate of 59 l/24h.
For SO2 the measuring ranges are approximately 0,1-80 ppb for a sampling period of one month. The corresponding range for NO2 is 0,02-40 ppb.The passive samplers are assembled and made ready for use at NILU. After exposure the samplers are usually returned to NILU where concentrations of SO2 are determined as sulphate by ion chromatography. NO2 and NH3 is determined by spectrophotometry.
Some examples of applications
Studies using passive sampling have been undertaken by NILU outdoor and indoor in Norway, Egypt, Russia and Venezuela. The sampling periods have varied from 1 day to one month dependent upon the general pollution levels.