In an urban-transit bus, fueled by biodiesel in Toledo, Ohio, single inhalable particle samples in October 2008 were collected and
detected by scanning electron microscopy and energy dispersive X-ray spectrometry (SEM/EDS). Particle size analysis found bimodal
distribution at 0.2 and 0.5 m. The particle morphology was characterized by 14 di erent shape clusters: square, pentagon, hexagon,
heptagon, octagon, nonagon, decagon, agglomerate, sphere, triangle, oblong, strip, line or stick, and unknown, by quantitative order.
The square particles were common in the samples. Round and triangle particles are more, and pentagon, hexagon, heptagon, octagon,
nonagon, decagon, strip, line or sticks are less. Agglomerate particles were found in abundance. The surface of most particles was coarse
with a fractal edge that can provide a suitable chemical reaction bed in the polluted atmospheric environment. The three sorts of surface
patterns of squares were smooth, semi-smooth, and coarse. The three sorts of square surface patterns represented the morphological
characteristics of single inhalable particles in the air inside the bus in Toledo. The size and shape distribution results were compared to
those obtained for a bus using ultra low sulfur diesel.