Odorous gas sampling is the first step of odour measurement by dynamic olfactometry. Filling a polymer bag (Tedlar, Nalophan…) with the odorous gas is quite easy for channeled gas releases (exhausts like chimneys) or for collectable gas releases (biofilter surface). For this last case, devices such hoods allow the isolation of a part of the surface to collect the emitted flux in direction to a tube to simulate a small chimney and then to be in similar conditions than for channeled gas releases. Sampling is more problematic with passive area sources (solid or liquid) i.e. without emitted air flux such as waste water lagoons, landfills, composting piles… For these situations, a lot of devices were developed to collect compounds emitted from an isolated part of the surface. But these devices influence emission conditions (equilibrium liquid/gas or solid/gas) comparatively to real situations. In addition, the device must not modify the temperature over the surface and must warranty the “natural” air flow over the source but in reality the impact of the device is important on the collected gas and also on the sample to be analyzed. Due to the influent parameters, the device istself presents a strong impact on the result. Five years ago, a study carried out by Ecole des Mines d’Alès, INERIS and IRSN on behalf ADEME and with members of AFNOR commission X43F, showed a huge variability of results depending on the sampling device. On a same source, measured odour flows were sometimes 100 or 1000 times higher with some devices comparatively to the lowest obtained value. The revision of the European standard EN13725 must indicate how to sample such a source but the ideal device doesn’t exist. So, about this subject, the objective of the standard revision is to define a compromise with a device that does not change the emission in order to have the more realistic value as possible. The paper describes the French intercomparison test of area sampling devices (both on solid and liquid sources) carried out on site. The objective is also to demonstrate the limits of some equipments for direct measurement.
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