an apparatus for sampling ambient air to obtain coarse and fine fractions of particulate matter includes a single acceleration tube and a collection tube coaxially arranged along a central axis with a gap between facing distal ends thereof within a range of d / d 1 of 1 to 2 , wherein d is the distance or gap between the distal ends and d 1 is the inside diameter of the outlet at the distal end of the acceleration tube . a housing surrounding the acceleration and concentration tubes is provided with a side - wall nozzle connected to a suction device for drawing a major portion of the sampled ambient air therethrough and for separation of particulate matter , as a fine fraction , from that major portion . a second suction device draws a minor portion of the sampled ambient air , containing the coarse fraction of the particulate matter , in a straight path approximating the central axis , through the acceleration tube and through the collection tube for passage through a filter for separation of the coarse fraction of particulate matter . the ratio of the flow rates of the major and minor portions of the sampled ambient air is adjusted to provide a cutpoint within the range of 2 - 3 microns . the apparatus is preferably operated with a flow rate for the sampled ambient air within the range of 900 - 1200 liters per minute .