The air we breathe is full of microscopic particles. This particulate matter is very complex, both in size and composition. Different components of particulate matter contain metal oxides, silica dust, and soot particles. Soot particles are a major form of air pollution in the industrialized world. Every combustion engine that runs, barbecues and campfires that are lit, and unwanted (natural) fires release huge amounts of soot particles into the atmosphere.