The diffusive sampling technique is based on the theory of molecular diffusion of gases, hence the term "diffusive sampling". The gas molecules diffuse into the sampler, where they are quantitatively collected on an impregnated filter or an adsorbent material, giving a concentration value integrated over time. No electricity, pump or other surrounding equipment is needed. Further, the samplers are small, light, cheap, soundless, re-usable and do not require electricity or calibration in the field.

Inorganic gases are absorbed by chemical reaction on a filter, impregnated with a solution specific to each pollutant measured. The reaction product, which is washed out of the filter prior to analysis, is specific to the particular gas in question. Organic gases, which do not react sufficiently fast with other chemicals, are instead trapped on an adsorbent material and subsequently desorbed thermally during the analysis.

The form of diffusive sampler used in this project for inorganic pollutants (SO₂ and NO₂) has been developed at IVL for measurements of ambient air pollutants. The sampler is 25 mm in diameter and 12 mm thick, mainly consisting of an impregnated filter and a diffusion barrier that keeps the sampling rate constant.

During transport and storage the sampler is placed in a plastic container. The sampling starts as soon as the container is opened and stops when the container is closed. The analyses are performed using ion chromatography for SO₂ and flow injection analysis for NO₂.

Volatile organic compounds are collected using diffusive samplers consisting of a tube of stainless steel, packed with an adsorbent material. The tubes are conditioned and analysed prior to sampling. During storage and transport the tubes are capped in both ends. When starting the sampling, one of the caps is removed and replaced by a diffusion cap. To avoid the migration of water droplets from outside the cap into the front gauze, a special, brimmed diffusion cap has been developed.

During sampling, the diffusion tube is oriented vertically with the diffusion cap down. A field blank consisting of a capped sampling tube is mounted in parallel with the diffusion tube. Re-capping the diffusion tube ends the sampling. The analyses are performed using a gas chromatograph with a flame ionisation detector (FID).