Source Characterization of Polycyclic Aromatic Hydrocarbons by Using Their Molecular Indices: An Overview of Possibilities - Reviews of Environmental Contamination and Toxicology - page 87

Methylphenanthrene (1-, 2-, 3- and 9-P1) ratios of the more stable ʲ isomers to
the less stable ʱ isomers (9-, 4- and 1-P1) have been developed for monitoring the
thermal maturity of oil and middle distillate fuels (Faksness et al. 2002 ; Stout et al.
2002 ; Uhler et al. 2007 ). The European Committee for Standardization (CEN)
includes the ratio of 2-P1/1-P1 (sometimes called the methylphenanthrene ratio or
MPR) in its methods for identifying different oil products, such as IFO 380 heavy
fuel oil (Hansen et al. 2007 ; Uhler et al. 2007 ). However, preferential biodegrada-
tion of 2-methylphenanthrene (Faksness et al. 2002 ) may reduce the value of
2-P1/1-P1, which can then be used as a biodegradation ratio (Wang and Brown
2009 ). In such a case, caution is necessary when utilizing this biodegradation index
for bunker fuels that may represent a blend of different oils and fuels, which conse-
quently have altered physicochemical properties (Wang and Brown 2009 ).
Another methylphenanthrenic ratio, the 4-P1 + 5-P1/P1, may be used to discrimi-
nate wood fires from coal combustion or asphalt (Simcik et al. 1999 ). Low values of
this ratio have been observed for oil (0.02), which can thus be discriminated from
other pyrogenic sources (Gschwend and Hites 1981 ).

5.3.7 Retene

The ratio of retene to chrysene (RET/C0) has been used to apportion softwood (e.g.,
fir and pine) combustion sources (RET/C0 = 4.5) and other combustion sources
(RET/C0 = 0.35) (Bogdal et al. 2011 ; Mathieu and Friese 2012 ; Yan et al. 2005 ,
2007 ). However, hardwood combustion may significantly reduce the RET/C0 ratio
(similar to the dimethylphenanthrene ratio: Sect. 5.3.8 ), which is insensitive to
inputs from the combustion of petroleum or of coal. It is thus recommended to use
the RET/C0 ratio together with other ratios such as the DMP ratio (Yan et al. 2005 ).
Roush and Mauro ( 2009 ) suggested that the RET/C0 ratio be used to distinguish
between coal fines (high value) and coal tar or petroleum products (low value).
Other RET ratios have occasionally been used. Dupree and Ahrens ( 2007 ) used
the retene to methylpyrene (RET/PY1) (three-/four-ringed alkyl PAHs) ratio to dis-
tinguish wood soot in urban runoff samples. The retene to pyrene (RET/PY0) ratio
was used to trace wood combustion in air (0.25-0.4) and sediments (Bucheli et al.
2004 and references cited by these authors). The RET/P4 ratio has been used to dis-
tinguish different spilled oil products according to the CEN methodology (Hansen
et al. 2007 ). Grimalt et al. ( 2004 ) suggested that the ratio of retene to benzo[ b ]
naphtho[ 2 , 1 - d ]thiophene, can be used together with the DMP ratio to distinguish
between wood combustion and sulfur pyrogenic sources such as coal combustion.

5.3.8 Dimethylphenanthrenes

17
17 26

,

The dimethylphenanthrene ratio (DMP ratio) is useful for distinguishing

, + ,

between vehicle emissions and wood combustion. The 1,7-dimethylphenanthrene
isomer is thermally unstable relative to 2,6-dimethylphenanthrene (by 3.3 kcal/