Source Characterization of Polycyclic Aromatic Hydrocarbons by Using Their Molecular Indices: An Overview of Possibilities - Reviews of Environmental Contamination and Toxicology - page 83

readily than A0 (Tobiszewski and Namiesnik 2012 and references cited by these
authors). Iqbal et al. ( 2008 ) noted that the P0/A0 ratio also depends on analytical
matrix effects.
When degradation significantly changes the P0/A0 ratio, consistency with other
ratios such as FL0/PY0 and P1/P0 has to be checked (Hwang et al. 2003 ). De Luca
et al. ( 2004 , 2005 ) noted that a prerequisite for the applicability of the P0/A0 is that
ʣPAH >0.22 ʼg/g dry weight. Furthermore, when P0/A0 values are close to the
pyrogenic/petrogenic thresholds, the ratio may be misleading for certain sources
such as automobile exhausts (Morillo et al. 2008b ). Dvorska et al. ( 2011 ) reported
that the P0/A0 ratio is not very useful for distinguishing between traffic and domes-
tic heating sources.
The P0/A0 ratio and other ratios such as FL0/PY0, BaA/C0 have been widely
applied (Budzinski et al. 1997 ; Sicre et al. 1987 ; Wang et al. 2001 , 2006 ; Yunker
et al. 2002 ). However, caution needs to be exercised when applying the P0/A0 ratio
for intermediate values (e.g., 4-15), on sediment that contains weathered PAH, or
for solely pyrogenic discriminations (Bucheli et al. 2004 ; Dvorska et al. 2011 ;
Hwang et al. 2003 ; Karlsson and Viklander 2008 ; Yan et al. 2005 ; Zhang et al.
2005 ). Thus, P0/A0 is more useful for petrogenic-pyrogenic discriminations.

5.3.3 The Ratio of Methylphenanthrenes to Methylanthracene

Methylphenanthrenes can be used to distinguish between petrogenic and pyrogenic
sources by comparing them with methylanthracenes that are mainly products of
catalytic or thermal cracking (Lake et al. 1979 ; Stout and Wang 2007 ; Uhler et al.
2007 ; Walker and Dickhut 2001 ). Such pyrolytic processes reduce the proportions of
9-, 4-, and 1-methylphenanthrenes in favor of methylanthracenes (Stout and Wang
2007 ). Therefore, a ʣP1/2-A1 (sum of methylphenanthrenes to 2-methylanthracene)
ratio might serve as an indicator of the presence of coal tar, or of cracked gas-oil
blending stock in heavy fuel oils (Uhler et al. 2007 ). Using this ratio it is also pos-
sible to distinguish heavy fuel oil from crude oil (Uhler et al. 2007 ).
Methylphenanthrenes are thermodynamically stable, and thus the ʣP1/2-A1
ratio should be high for most crudes and higher rank coals, which are produced dur-
ing different geologic periods and under different heating conditions.
Methylanthracenes may rapidly decompose to methylphenanthrenes (Walker and
Dickhut 2001 ). Furthermore, the ʣP1/2-A1 ratio is sensitive to different source
inputs, which may significantly alter its value (Walker and Dickhut 2001 ).

5.3.4 Methylphenanthrene Plus Methylanthracene Versus Their Parents

A sensitive indicator for tracing petrogenic and pyrogenic PAHs is the ratio of meth-
ylphenanthrene plus methylanthracene to the sum of parent phenanthrene plus
parent anthracene: PA
PA

11
00

+
+

, or PA1/PA0 in short (Fig. 10 ) (Da Silva and Bicego

2010 ; Mitra et al. 2009 ; Yan et al. 2005 ; Yunker et al. 2002 ). High PA1/PA0 ratios
(>1.5) generally indicate petroleum, but occasionally PA1/PA0 is greater than 1.5