Coarse Dust Recorder

The Coarse Dust Recorder has a tube at the end of which is a fan that creates a constant air velocity of 8.8 m/s in the tube. The recorder's air intake is kept pointed towards the wind by means of a weather vane.
Positioned in front of the fan is a cassette containing a strip coated with an adhesive; the strip is 5 mm wide and 12 m long. Consecutive sections of strip 20 mm long are exposed to the airflow. Depending on the air velocity and strip width, the larger particles are collected by the strip, while smaller particles are carried along past the strip by the airflow. There is a gradual transition from small to large particles. The 50% cut-off aerodynamic diameter is 14 µm. The following figure gives the collection efficiency as a function of particle size.


Figure 1 The collection efficiency of the Coarse Dust Recorder

The sampled dust is analysed using an automatic image analysis system. In this, the effective area coverage (EAC) and particle size distribution are determined. The effective area coverage is converted into the coarse dust concentration is calculated by means of an experimentally assessed conversion factor.



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