Source Characterization of Polycyclic Aromatic Hydrocarbons by Using Their Molecular Indices: An Overview of Possibilities - Reviews of Environmental Contamination and Toxicology - page 85

5.3.5 Ratio of Methylphenanthrenes to Phenanthrene

After carbonaceous materials are combusted at 600-1,500 °C, phenanthrene domi-
nates over its alkylated homologues, which are negligible (Lehndorff and Schwark
2009 ). High ratios of methylphenanthrenes (the sum of 1- plus 2-, and optionally
3- plus 9-methylphenanthrenes) over phenanthrene (P1/P0) indicate combustion at
low temperatures that preserve the petrogenic alkylation pattern, e.g., fossil fuels,
products of petroleum diagenesis, inefficient combustion, etc. (Elmquist et al. 2007 ;
Lehndorff and Schwark 2009 ; Luo et al. 2008 ; Mitra et al. 1999 ; Takada et al. 1990 ).
In petrogenic sources such as unburned fossil organic material, petroleum, oil
shales, and their refined products, the P1/P0 ratio displays values over 2 (Gschwend
and Hites 1981 ; Hwang et al. 2003 ; Kim et al. 2008 ; Luo et al. 2008 ; Takada et al.
1990 ; Zakaria et al. 2002 ). When P1/P0 < 1 (Budzinski et al. 1997 ; Hwang et al. 2003 ;
Takada et al. 1990 ), or 0.4 < P1/P0 < 0.7, according to Elmquist et al. ( 2007 ) a pyro-
genic origin may be inferred. Indeed, in Fig. 11 , the area of overlap between pyro-
genic and petrogenic sources (coal, used lubricants, automobile exhausts) is mainly
the interval 1 < P1/P0 < 2. Because phenanthrene is less stable than its methyl homo-
logues, the degradation of crude or diesel increases the P1/P0 (Burns et al. 1997 ).
The methylphenanthrenes to phenanthrene ratio has been used to identify pyro-
genic or petrogenic hydrocarbon contaminants (e.g., Farrington et al. 1977 ; Guo et al.
2007 ; Luo et al. 2008 ), or, together with the dimethylphenanthrene (DMP) ratio, to
trace PAH sources over time (Sect. 5.3.8 ) (Elmquist et al. 2007 ). The P1/P0 ratio has
also been used to distinguish asphalt from vehicle emissions (along with the D1/P1
ratio-methyldibenzothiophenes to methylphenanthrenes), and vehicle traffic (0.7 to
8.2) from background domestic pollution (0.7-1.2) in Tokyo (Takada et al. 1990 ).
Used oil or diesel emissions have both petrogenic (unburned fuel, P1/P0 > 2) and
pyrogenic (HMW) PAH signatures (Mostafa et al. 2009 ; Zakaria et al. 2002 ).
Therefore, the P1/P0 ratio is usually higher in diesel vehicle emissions than in gaso-
line ones (Hwang et al. 2003 ; Larsen and Baker 2003 ). Accordingly, Hwang et al.
( 2003 ) calculated the diesel and gasoline vehicle contributions to pine needles via a
mass balance model. Furthermore, pyrogenic contribution from used crankcase oil
could cause the P1/P0 ratio to be correlated with chrysene, benzo[ a ]pyrene,
benzo[ ghi ]perylene and the total PAHs (Zakaria et al. 2002 ).

5.3.6 Distribution of Methylphenanthrenes

Alkylphenanthrene homologues are considered as petrogenic markers and enable
petrogenic PAHs to be recognized (Gogou et al. 2000 ). For example, if P2 > P1 + P0
(dimethylphenanthrenes concentration is higher than the sum of the concentra-
tions of methylphenanthrene plus phenanthrene), then the dominant source is
petroleum (Gogou et al. 2000 ; Sicre et al. 1987 ). However, coal combustion
and wood smoke may show maxima in the parent PAH, or the methyl-PAH, or
the dimethyl-PAH (Sicre et al. 1987 ; Yunker et al. 2002 ). Furthermore, coal PAHs
(Fig. S27, Supporting Material) do not follow the “usual” pyrogenic or petrogenic