The passive sampling method allows the use of simple equipment to determine NO2 nitrogen dioxide and benzene concentrations at specific locations. Establishing a network with several measurement points is quick and requires little equipment. Passive samplers (cylindrical tubes of 3 to 7 cm long and 1 cm in diameter)are exposed to the open air for a fixed period, in about 3 meters high.By simple diffusion of the pollutant in the air, it is going to be trapped by the sampler. Usually the passive diffusion tubes are installed in narrow streets which are strongly influenced by traffic.