Source Characterization of Polycyclic Aromatic Hydrocarbons by Using Their Molecular Indices: An Overview of Possibilities - Reviews of Environmental Contamination and Toxicology - page 81

alkylated chrysenes (e.g., N1-N4/C1-C3) (Bence et al. 1996 ; Boehm et al. 2008 ;
Wang et al. 2006 ). After the rapid dissolution of the parent naphthalene and methyl-
naphthalenes, these ratios decrease more slowly (Bence et al. 1996 ).

5.3.2 The Ratio of Phenanthrene to Anthracene

The ratio of parent phenanthrene to parent anthracene (P0/A0) redundant has been
extensively used to differentiate between petrogenic and pyrogenic PAH pollution in
sediments (e.g., Grimmer et al. 1981 ; Gschwend and Hites 1981 ; Guo et al. 2007 ;
Lake et al. 1979 ; Sicre et al. 1987 ). Thermodynamically, this ratio is temperature-
dependent (Budzinski et al. 1997 and references therein). Phenanthrene is the ther-
modynamically most stable triaromatic isomer, and its prevalence over A0 supports
petrogenesis (Budzinski et al. 1997 ; De Luca et al. 2004 , 2005 ; Gogou et al. 2000 ).
High-temperature (800-1,000 K) processes yield low P0/A0 ratio values (4-10),
usually less than 5. The slow thermal maturation of organic matter in petroleum leads
to much higher P0/A0 values (50 at 373 K) (Budzinski et al. 1997 ; De Luca et al.
2005 ; Neff et al. 2005 ; Wang et al. 2001 ). However, fresh petroleum products occa-
sionally exhibit small P0/A0 values (down to 4), whereas some combustion sources
have a higher value (Budzinski et al. 1997 ; Colombo et al. 1989 ; Wang et al. 1999a ).
P0/A0 ratios in different literature data sources are summarized in Fig. 9 . Also
shown in Fig. 9 are the P0/A0 threshold values that researchers used to distinguish
petrogenic from pyrogenic sources. For example, P0/A0 > 15 for likely petrogenic
inputs (or >30 for negligible pyrogenic) and P0/A0 < 15 for the dominance of pyro-
lytic sources (<5 according to Neff et al. 2005 ), such as fuel combustion or other
high-temperature processes (Budzinski et al. 1997 ; De Luca et al. 2004 ; Morillo
et al. 2008a ). Yunker et al. ( 2002 ) concluded that a lowest P0/A0 boundary of 9 or
10 appears applicable for petrogenics, except that P0/A0 ratios overlap for certain
sources such as diesel oils, coals, and coal emissions (Fig. 9 ).
In summary: i) P0/A0 > 30 shows crude oil contamination, but creosote and the
combustion of some coals or crude occasionally exhibit high P0/A0 ratios, ii) values
30 > P0/A0 > 10 show a mixed source profile, but if diesel and coal combustion and
creosote are ruled out, then such values indicate a probable petrogenic source, iii)
values 10 > P0/A0 > 5 define a mixed source profile, and iv) values smaller than 5
indicate pyrogenic origin except for gasoline fuel, some road fingerprints, and low
rank coals that exhibit 5 < P0/A0 < 9.
The different thermodynamic stabilities of P0 and A0 allow biogeochemical pro-
cesses to alter the P0/A0 value (Bucheli et al. 2004 ; Lake et al. 1979 ; Yan et al.
2006 ). The phenanthrenes photodegrade much more slowly than anthracenes
(Behymer and Hites 1988 ; Hwang et al. 2003 ). As a result, smaller quantities of A0
are observed during the daytime in urban areas (Yunker et al. 2002 ). However,
Zhang et al. ( 2005 ) calculated an air-to-sediment (i.e., receptor-to-source) ratio
to be approximately 1 for P0/A0. This indicated that the P0/A0 ratio does not
change significantly during deposition from atmospheric emissions to sediment.
Nevertheless, the P0/A0 is sensitive to parameters such as molecular mobility and
volatility (Zhang et al. 2005 ).