Source Characterization of Polycyclic Aromatic Hydrocarbons by Using Their Molecular Indices: An Overview of Possibilities - Reviews of Environmental Contamination and Toxicology - page 112

The ratio of the sum total of four- to six-ringed PAHs (including parent and alkylated
homologues) to total PAHs (Ring456/TPAH) is minimally influenced by the degrada-
tion of LMW PAHs (Yan et al. 2005 , 2006 ). Ring456/TPAH is sensitive to inputs from
fresh oil spills, and thus can be used to distinguish petrogenic (<0.4) and pyrogenic
(>0.5) inputs (Yan et al. 2005 , 2006 ). In the study of Yan et al. ( 2006 ), Ring456/TPAH
correlated with FL0/PY0, but weathering rendered the Ring456/TPAH insensitive to
petrogenic contributions. Furthermore, the applicability of the Ring456/TPAH is cur-
rently limited because of the small amount of data available to validate this ratio, par-
ticularly for environments where petrogenic sources are dominant (Yan et al. 2006 ).

5.8.4 Pyrogenic Index

The pyrogenic index (PI) is the ratio of the sum of the concentrations of EPA prior-
ity unsubstituted three- to six-ring PAHs (sometimes coronene is also added: Wang
et al. 2006 ) to the sum of the concentrations of the five target alkylated PAH homo-
logues (ʣ5alkylated: naphthalenes, luorenes, dibenzothiophenes, phenanthrenes
and chrysenes) (Wang et al. 1999b , 2001 , 2014 ):

= ++++++++++++
−

AY AE A P aA BbFBkF BePBaP Per ghi 0 0

14 1

IP DA

PI

( ) + ( ) +− ( ) +− ( ) +− ( )

N P − 4 D 1 4 F 0 4 C 0 4

PI ranges from 0.8 to 2.0 for pyrogenic sources and is much lower for petrogen-
ics: <0.01 for crudes and <0.05 for heavy oils and heavy fuels (Fig. 24 ; Wang et al.
1999a , b , 2001 , 2009 ). Thus, PI can be useful for distinguishing heavy fuels from
crude oils or light refined products, and soot from crude oils or petroleum products
(De Fatima et al. 2007 ; Wang et al. 1999a , b , 2001 ).
Compared with other indices, PI better resolves pyrogenic and petrogenic prod-
ucts (combustion significantly alters the value of PI) and is more accurate and con-
sistent (Wang et al. 1999a , b ). In contrast to combustion, weathering has little effect
on PI, which makes it one of the most reliable PAH indices.

5.8.5 Fossil Fuel Pollution Index

A precursor to PI for differentiating pyrogenic and petrogenic products is the fossil
fuel pollution index (FFPI) (Iqbal et al. 2008 ; Stout et al. 2001b ), defined as:

1
2 01234

( ) +++

NNNNNDDDDP PPPP 012340123 +++++++++ +

FFPI =

TPAH

FFPI is close to zero for most pyrogenic PAHs, whereas for sediments containing
significant amounts of fossil-fuel PAH constituents, the FFPI is close to 1 (Iqbal
et al. 2008 ). FFPI can thus be used as a method for apportioning the contribution of
different PAH sources.