A dust sampling instrument comprising a D.V.P. Mark 11 pump with a swept volume of 90 cm₃. A filter paper is inserted into a bridge behind the inlet nozzle of the pump such that a circle of 1-cm diameter of the filter paper is exposed to the dust. The dust, while passing through the filter paper, produces a stain. The optical density of the stain is determined photoelectrically in a densitometer by the light that falls upon a galvanometer. The dust particle concentration is evaluated by a calibration factor. Its main disadvantage is that it underestimates the number of fine particles.