Soot /ˈsʊt/ is a mass of impure carbon particles resulting from the incomplete combustion of hydrocarbons. Soot causes cancer and lung disease, and is the second-biggest human cause of global warming, Soot as an airborne contaminant in the environment has many different sources, all of which are results of some form of pyrolysis. Soot in very low concentrations is capable of darkening surfaces or making particle agglomerates, such as those from ventilation systems, Soot is the primary cause of ghosting, the discoloration of walls and ceilings or walls and flooring where they meet. It is generally responsible for the discoloration of the walls above baseboard electric heating units, the formation of soot depends strongly on the fuel composition. The rank ordering of sooting tendency of fuel components is, naphthalenes → benzenes → aliphatics, however, the order of sooting tendencies of the aliphatics varies dramatically depending on the flame type. The difference between the tendencies of aliphatics and aromatics is thought to result mainly from the different routes of formation. The formation of soot is a process, an evolution of matter in which a number of molecules undergo many chemical and physical reactions within a few milliseconds. Soot is a form of amorphous carbon. Gas-phase soot contains polycyclic aromatic hydrocarbons, the PAHs in soot are known mutagens and are classified as a known human carcinogen by the International Agency for Research on Cancer. Soot forms during incomplete combustion from precursor molecules such as acetylene and it consists of agglomerated nanoparticles with diameters between 6 and 30 ㎚. The soot particles can be mixed with metal oxides and with minerals, many details of soot formation chemistry remain unanswered and controversial, but there have been a few agreements, Soot begins with some precursors or building blocks. Nucleation of heavy molecules occurs to form particles, surface growth of a particle proceeds by adsorption of gas phase molecules. Coagulation happens via reactive particle–particle collisions, oxidation of the molecules and soot particles reduces soot formation. Soot, particularly diesel exhaust pollution, accounts for one quarter of the total hazardous pollution in the air. Among these diesel emission components, particulate matter has been a concern for human health due to its direct. In earlier times, health professionals associated PM10 with chronic disease, lung cancer, influenza, asthma. However, recent scientific studies suggest that these correlations be more linked with fine particles. Long-term exposure to air pollution containing soot increases the risk of coronary artery disease
Emission of soot in the fumes of a large diesel truck, without particle filters
The black staining on the power car of this Midland MainlineInterCity 125 High Speed Train is the result of soot building up on the train's surface.