Source Characterization of Polycyclic Aromatic Hydrocarbons by Using Their Molecular Indices: An Overview of Possibilities - Reviews of Environmental Contamination and Toxicology - page 80

account for other kinds of degradation (biotic or abiotic), if a model describes them
adequately. Several authors have evaluated the different types of degradation that
affects PAH ratios (e.g., Costa and Sauer 2005 ; Stout et al. 2003 ; Uhler and Emsbo-
Mattingly 2006 ; Wang et al. 1998 ). Hence, different PAH ratios may also be used as
a simple means of evaluating degradation.

5.2 Sum of PAHs

A way to quantify the amount of pollution for a specific area, and also to take the
first step in characterizing a PAH source, is to compare the sum of PAHs with the
amounts released by a suspected source (Dupree and Ahrens 2007 ; Saber et al. 2005 ,
2006 ; Stout 2007 ). “Total PAHs” is commonly defined as the sum of identified
three- to six-ringed parent PAH compounds, which is denoted as ʣPAH or EPA 16
(i.e., the U.S. EPA sixteen priority PAHs). To account for uncombusted petroleum
sources that are rich in alkyl PAHs, TPAH is defined as the sum of all quantified
parent and alkyl PAHs (Stout et al. 2003 ; Yan et al. 2006 ). Sometimes naphthalene,
perylene and retene are excluded from TPAH estimation because the naphthalene is
a common laboratory contaminant and perylene and retene could have a non-anthro-
pogenic origin (Boehm et al. 2001 , 2002 , 2007 ; Gogou et al. 2000 ).

5.3 Low Molecular Weight PAH Ratios

5.3.1 Naphthalene Indices

Naphthalene and alkyl naphthalene ratios find several applications in source
identification, as they constitute potentially useful thermal (Stout et al. 2002 ) or
weathering parameters for crudes, coals, bitumen and other sources. Roush and
Mauro ( 2009 ) used the N0/N1 ratio (parent naphthalene over methylnaphthalene) to
detect coal tar residues enriched in naphthalene oil. The ratio MNR = 2-N1/1-N1
(2-methylnaphthalene to 1-methylnaphthalene) is unaffected by light weathering
and can be used to distinguish products that have different methylnaphthalene con-
tent, such as lightly weathered distillates (Stout and Wang 2007 ). MNR and other
alkylnaphthalenic ratios were used for the characterization of coals of different
ranks (Radke et al. 1982 ). For minimally weathered sediments, the petrogenic back-
ground may be deduced simply from a high N0/F0 (naphthalene to fluorene) ratio
(Neff et al. 2006 ).
In the initial weathering stages of an oil spill, the loss of naphthalene and meth-
ylnaphthalenes relative to dimethylnaphthalenes (N0 + N1/N2) can be used as a
measure for the loss of PAHs due to dissolution (Diez et al. 2007 ). The N3/P3 (tri-
methyl naphthalenes over trimethylphenanthrenes) ratio is useful for estimating the
weathering state of light crude oils (Peters et al. 2005 ). Heavier weathering may be
evaluated by the sum of alkylated naphthalenes over TPAH or over the recalcitrant