A plain-jet external-mixing, airblast atomizer has been studied. A bimodal drop size distribution behavior has been observed, where two different drop size populations have been identified. It was observed that as a result of the impingement of the air stream on the liquid jet, a portion of the liquid flows back toward the orifice, arrives at the orifice surface, spreads outward as a thin film in the radial direction, and is then atomized by the air stream emerging from the annular slot. While the large-drop population is generated by the atomization process occurring at the liquid-air collision region, the small-drop population Is generated by the backflow mechanism. This phenomenon has been studied experimentally and an approximate analysis has been proposed to describe it.