The morphology of the coal from the smoldering cigarette was characterized using light microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), inductively coupled plasma spectroscopy, and image analysis. The coal of the smoked cigarette was divided into four regions: the char positioned at and behind the char line of the cigarette paper, the coal base located just in front of the char line, the coal tip located in front of the coal base, and the ash that surrounded the exterior surface of the coal cone. The morphology of the char behind the coal consisted of tobacco shreds that transitioned from yellow to brown to black with changes in morphology from minimal surface damage to cuticle separation. The blackened area of the coal base contained shreds that exhibited vesicle formation to carbonized shells to inorganic encrustation of the shreds, all of which are characteristic morphologies of pyrolysis. Shreds within the coal tip region exhibited morphologies similar to those found in the coal base as well as progressive cell wall degradation through etching, morphology that is characteristic of oxidative pyrolysis. Shred structures from the ash region consisted of inorganic replicas of the tobacco shreds to materials that consisted of melts of inorganic components. Some of the potassium, sulfur, and sodium from the tobacco migrated into the gas stream.
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