Soot


Soot
Emission of soot from a large diesel truck, without particle filters

Soot (play /ˈsʊt/) is a general term that refers to impure carbon particles resulting from the incomplete combustion of a hydrocarbon. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolyzed fuel particles such as cenospheres, charred wood, petroleum coke, and so on, that may become airborne during pyrolysis and that are more properly identified as cokes or chars. The gas-phase soots contain polycyclic aromatic hydrocarbons (PAHs).[1] The PAHs in soot are known mutagens [2] and are classified as a "known human carcinogen" by the International Agency for Research on Cancer (IARC).[3]

Soot, as an airborne contaminant in the environment has many different sources but they are all the result of some form of pyrolysis. They include soot from internal combustion engines, power plant boilers, hog-fuel boilers, ship boilers, central steam heat boilers, waste incineration, local field burning, house fires, forest fires, fireplaces, furnaces, etc. These exterior sources also contribute to the indoor environment sources such as smoking of plant matter, cooking, oil lamps, candles, quartz/halogen bulbs with settled dust, fireplaces, defective furnaces, etc. Soot in very low concentrations is capable of darkening surfaces or making particle agglomerates, such as those from ventilation systems, appear black. 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 and can be know as a gas. The formation of soot depends strongly on the fuel composition.[4] The rank ordering of sooting tendency of fuel components is: naphthalenes → benzenes → aliphatics. However, the order of sooting tendencies of the aliphatics (alkanes, alkenes, alkynes) varies dramatically depending on the flame type. The difference between the sooting tendencies of aliphatics and aromatics is thought to result mainly from the different routes of formation. Aliphatics appear to first form acetylene and polyacetylenes; aromatics can form soot both by this route and also by a more direct pathway involving ring condensation or polymerization reactions building on the existing aromatic structure .[5][6]

Contents

Description

Soot is a powder-like form of amorphous carbon.

Hazards

Soot is in the general category of airborne particulate matter, and as such is considered hazardous to the lungs and general health when the particles are less than five micrometres in diameter, as such particles are not filtered out by the upper respiratory tract.[citation needed] Smoke from diesel engines, while composed mostly of carbon soot, is considered especially dangerous—owing both to its particulate size and to the many other chemical compounds present.[citation needed]

Long-term exposure to urban air pollution containing soot increases the risk of coronary heart disease, according to a major study published in New England Journal of Medicine in 2007.[7] Diesel exhaust (DE) gas is a major contributor to combustion derived particulate matter air pollution. In several human experimental studies using a well-validated exposure chamber setup DE has been linked to acute vascular dysfunction and increased thrombus formation.[8][9] This serves as a plausible mechanistic link between the previously described association between particulate matter air pollution and increased cardiovascular morbidity and mortality.

See also

References

  1. ^ Rundel, Ruthann, "Polycyclic Aromatic Hydrocarbons, Phthalates, and Phenols", in Indoor Air Quality Handbook, John Spengleer, Jonathan M. Samet, John F. McCarthy (eds), pp. 34.1-34.2, 2001
  2. ^ Rundel, Ruthann, "Polycyclic Aromatic Hydrocarbons, Phthalates, and Phenols", in Indoor Air Quality Handbook, John Spengleer, Jonathan M. Samet, John F. McCarthy (eds), pp. 34.18-34.21, 2001
  3. ^ Soots (IARC Summary & Evaluation, Volume 35, 1985)
  4. ^ Seinfeld, John H. ; Pandis, Spyros N. Atmospheric Chemistry and Physics - From Air Pollution to Climate Change (2nd Edition).. John Wiley & Sons.
  5. ^ Graham, S. C, Homer, J. B., and Rosenfeld, J. L. J. (1975) "The formation and coagulation of soot aerosols generated in pyrolysis of aromatic hydrocarbons", Proc. Roy. Soc. Lond. A344, 259-285.
  6. ^ Flagan, R. C., and Seinfeld, J. H. (1988) Fundamentals of Air Pollution Engineering, Prentice-Hall, Englewood Cliffs, NJ.
  7. ^ "Long-Term Exposure to Air Pollution and Incidence of Cardiovascular Events in Women" Kristin A. Miller, David S. Siscovick, Lianne Sheppard, Kristen Shepherd, Jeffrey H. Sullivan, Garnet L. Anderson, and Joel D. Kaufman, in New England Journal of Medicine February 1, 2007
  8. ^ "Diesel exhaust inhalation increases thrombus formation in man", Andrew J. Lucking, Magnus Lundback, Nicholas L. Mills, Dana Faratian, Stefan L. Barath, Jamshid Pourazar, Flemming R. Cassee, Kenneth Donaldson, Nicholas A. Boon, Juan J. Badimon, Thomas Sandström, Anders Blomberg, and David E. Newby1
  9. ^ "Persistent Endothelial Dysfunction in Humans after Diesel Exhaust Inhalation", Håkan Törnqvist, Nicholas L. Mills, Manuel Gonzalez, Mark R. Miller, Simon D. Robinson, Ian L. Megson, William MacNee, Ken Donaldson, Stefan Söderberg, David E. Newby, Thomas Sandström, and Anders Blomberg

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