These images show the mixing and classification of soot particles. The field-emission scanning electron microscope images of four different categories of soot particles are: (a) embedded, (b) partly coated, (c) bare and (d) with inclusions. Approximately 50 percent of the ambient soot particles are embedded, 34 percent are partly coated and 12 percent have inclusions. Only 4 percent of the particles are bare soot (not coated or very thinly coated). Scale bars, 500 nm. Right, spherical tar balls dominate in the emissions.