1. 3. Passive sampler for SO2 and NO2, http://www.nilu.no/AQM/2b_passiv_sampler.htm.
2. 4. Rupprecht & Patashnick Co., Inc., High-Quality Passive Sampling of NO, NO2, NOx, SO2 and O3 in Indoor or Outdoor Environments, www.passivesampling.com.
3. 5. Measurements, http://medias.obs-mip.fr/idaf/maquette/measurements/Gas.html.