The Tunnel Impactor is developed to enable the determination of the mass concentration and mass size distribution of coarse aerosol from the ambient atmosphere. The instrument consists of a large wind-directed tube functioning as an aerosol inlet. Further down the tube four impactors are mounted, each with different dimensions (2, 5, 15 and 50 mm wide ribbons), thus offering different cut-off characteristics. A constant air flow through the tube is accomplished by four fans, mounted at the rear end, in order to keep impaction conditions constant and well defined. The experimentally assessed cut-off diameters are in the range from 10 to 60 µm.

The instrument was found to perform properly under ambient conditions at windspeeds above 1 m/s up to 7.5 m/s. In the windtunnel, it is frequently used to study aerodynamic properties of different sorts of dust. up