particulates - atmospheric particles made up of a wide range of natural materials (e.g., pollen, dust, resins), combined with man-made pollutants (e.g., smoke particles, metallic ash); in sufficient concentrations, particulate scan be a respiratory irritant. Primary sources of man-made particulate emissions are industrial process losses (e.g., from cement plants) and stationary combustion sources. Motor vehicles contribute a relatively minor amount of particulates. See emissions (stationary source), pollutants.