A mobile harvesting unit which utilizes a high volume fan to separate crops from foreign matter, has a dust suppression system which substantially reduces particulates which are discharged with the fan exhaust. The dust suppression system has two stages. The first stage separates larger particles of foreign matter by deploying an air stream cleaning chain upstream of the fan. The second stage is contained within a air stream discharge duct. Within the air stream discharge duct, a liquid, such as water, is sprayed into the dust entrained air stream. The moistened air stream flows through a plurality of collection members which extend radially from a brush drum, where the moistened dust particles are accumulated on the collection members, such that the volume of dust particles contained within the air discharged from the harvesting unit is substantially reduced.