Electron microscopic characterization of exhaust particles containing lead dibromide beads expelled from aircraft burning leaded gasoline.

Piston powered aircraft burning leaded gasoline contribute ~70% of the lead in the atmosphere in the US. The physical size, composition, and structure of aircraft exhaust particles containing lead dibromide are poorly understood and heretofore have not been examined directly by electron microscopy (EM), in particular when captured from an aircraft in flight. To accomplish this, exhaust samples were trapped on EM supports within 10-15 ms of exiting the aircraft exhaust pipe. High angle annular detector dark field scanning EM revealed irregular particles with a mean diameter of 13 nm consisting of a 4 nm microcrystal of lead dibromide surrounded by a halo of hydrocarbons. In contrast, exhaust particles from an automobile burning leaded fuel averaged 35 nm in diameter and contained 5-10, 4 nm lead beads. Of significant concern, the smaller aircraft particles could penetrate mucosal barriers in the lung and be readily taken up by epithelial cells.