Representative sampling of aerosols

In order to obtain representative samples of aerosol, without deviations in particle size distribution, properly designed and positioned measurement probes are required. The particle settling velocity has to be known for proper selection of probes and probe positioning. using the settling velocity, it can be determined whether or not the criteria for stationary aerosol are applicable as well as the ideal probe design for each individual sampling situation. In order to obtain representative samples of non-stationary aerosol, properly designed and positioned isokinetic probes are required. The isokinetic probes assure that the same flow velocity is obtained in the probe as in the surrounding environment. Isokinetic probes must be positioned head on against the flow direction. In sampling of stationary aerosol, the probes have to be designed so as to avoid deviations in the sampled particle size distribution due to particle inertia and settling velocity. Probes designed for stationary conditions are preferably positioned horizontally but other inclinations are possible if the probes´ design permits it. Probe design is dependent on the sample to which the instrument is connected, the density and size of the aerosol particle, the density and viscosity of the gas phase of the aerosol and, in certain cases, the cross-section area of the duct the aerosol is moving through.