General Information about PAHs

Summary

--- PAHs are products of incomplete combustion and are widely produced by industrial processes.
--- Certain PAHs are carcinogenic.
--- Particulate matter (less than 2.5 micron) acts as a carrier for PAHs into the human body.

What are PAHs?

PAH is an acronym for Polycyclic Aromatic Hydrocarbon (sometimes the term Polynuclear is also used).

How are PAHs formed?

PAHs are products of incomplete combustion. Inefficient combustion of solid and liquid fuels such as coal, wood, kerosene and fuel oil can lead to PAH formation.

 
What are the common sources of PAHs? (Ref. 1)

Mobile Sources:	Diesel and gasoline engines
Workplace Environments:	Service stations, coke ovens and tar plants
Combustion Burners:	Heaters, boilers and furnaces
Industrial Incinerators :	Municipal, hazardous and hospital wastes
Domestic Activities:	Cigarette smoke, wood and kerosene stoves, oil burners, barbecues
Industrial processes:	Petroleum catalytic cracking, iron and steel foundries, aluminum production and carbon black manufacture

Are PAHs regulated in the USA? (Ref. 2)

Under the Clean Air Act Amendments, the list of hazardous air pollutants to be regulated include Polycyclic Organic Matter (POM) -- organic compounds with more than one benzene ring, and which have a boiling point greater than or equal to 100 ºC. Most PAHs fall under the category of POM.

Which are the typical PAHs?

Naphthalene	Acenaphthylene	Acenaphthene	Fluorene
Phenanthrene	Anthracene	Fluoranthene	Pyrene
Chrysene	Benz(a)anthracene	Benzo(k)fluoranthene	Benzo(b)fluoranthene
Benzo(a)pyrene	Indeno(1,2,3cd)pyrene	Dibenzo(a,h)anthracene	Benzo(g,h,i)perylene

 
Particulate-bound versus vapor phase fractions (Ref. 3)

High molecular weight PAHs are predominantly adsorbed on soot and particulate matter (due to the low vapor pressure).
The ratio of the amount of a PAH present in the particulate-bound phase to the amount present in the vapor phase is dependent upon the specific PAH and the system properties (particulate loading and temperature).

Toxicity (Ref. 4) 

Toxicological studies have identified several PAHs as being carcinogenic. Some of the carcinogenic PAHs are Benzo(a)pyrene, Benzo(b)fluoranthene, Benzo(a)anthracene and Benzo(c)phenanthrene.

Particulate fraction for health concerns (Ref. 5)

Ultrafine particles (less than 2.5 microns) are not removed by the upper respiratory tract and are carried into the lungs. These ultrafine particles act as carriers of chemicals (like PAHs) into the human body.

Current methods for PAH sampling and analysis (Ref. 6) 

Currently, PAHs are measured using a sampling train (MM-5, CARB 429, high/low volume samplers) followed by analysis using HPLC or GC/MS.  

 
References

1) Locating and Estimating Air Emissions from sources of Polycyclic Organic Matter (POM), USEPA, Research Triangle Park, PB88-149059, 1987.
2) The New Clean Air Act, A Guide to the Clean Air Program as amended in 1990, Morgan, Lewis and Bockius, Washington, D.C., 1990.
3) S.O.Baek et al, Phase distribution and particle size dependency of PAHs in urban atmosphere, Chemosphere, Vol.22, No.5-6, 503-520, 1991.
4) A.Dipple, Polycyclic Aromatic Hydrocarbon Carcinogenesis, Polycyclic Hydrocarbons and Carcinogenisis, ACS Symposium Series 283, Washington, D.C., 1985.
5) Ledbetter, L.W., Air Pollution, Dekker, New York, 1972.
6) Determination of Polycyclic Aromatic Hydrocarbon (PAH) emissions from stationary sources, Method 429, California Air Resources Board, 1989.

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