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PETROLEUM AND INDMDUAL POLYCYCLIC AROMATIC HYDROCARBONS

2,6-Dimethylnaphthalene

CH₃

7,12-Dimethylbenz[a]anthracene

1 -Methylphenanthrene

Dibenzofuran

Quinoline

NH,

1-Naphthylamine

Dibenzothiophene

Figurę 14.3 Examples of PAH compounds with attached alkyl groups and aromatic compounds with nitrogen, sulfur, or oxygen.⁸ Except for the alkyl groups, hydrogen atoms bonded to carbon atoms are omitted.

14.3.2 PAHs

Most PAHs are formed by a process of thermal decomposition (pyrolysis) and subseąuent recombination (pyrosynthesis) of organie molecules.¹⁶ Incomplete combustion of organie matter produces PAHs in a high-temperature (500 to 800°C) environment. Ali forms of combustion, except flammable gases well mixed with air, produce some PAHs. Subjection of organie materiał in sediments to a low-temperature (100 to 300°C) environment for long periods of time produces PAHs as coal and oil deposits within sedimentary rock formations (a.k.a. diagenesis).⁷-¹⁷ Although the PAH compounds formed by high- and low-temperature processes are similar, the occurrence of alkylated PAHs is greater in the low-temperature process.¹⁴ Biological formation of PAHs occurs in chlorophyllous plants, fungi, and bacteria.²⁸

Natural sources of PAHs include forest and grass fires, oil seeps,; yolcanoes, plants, fungi, and bacteria. Anthropogenic sources of PAHs include petroleum, electric power generation, refuse incineration, and home heating; production of coke, carbon black, coal tar, and asphalt; and intemal combustion engines.²’⁷ The primary mechanism for atmospheric contamination by PAHs is incom-