Source Characterization of Polycyclic Aromatic Hydrocarbons by Using Their Molecular Indices: An Overview of Possibilities - Reviews of Environmental Contamination and Toxicology - page 100

burned oils (Hegazi and Andersson 2007 ; Wang and Fingas 1995 ). Wang and Fingas
( 1995 , 2003 ) established a database of the methyldibenzothiophene ratios for
crudes, weathered and biodegraded oils, and other petroleum products. The ratios
pair of 11
41

−
−

D

D versus 2131

−+−
−

DD
D

exhibits a satisfactory discriminating ability

41

for different oils (Hegazi and Andersson 2007 ). Alternatively, such ratios may be
used as biodegradation indicators, because 1-D1 is most affected by biodegradation,
whereas 2-D1 and 3-D1 are the least affected by biodegradation (Faksness et al.
2002 ; Hegazi and Andersson 2007 ). Therefore, prior knowledge of the weathering
state of a sample is necessary before the methyldibenzothiophene ratios can be used
either as source or weathering indicators (Wang and Fingas 1995 ). Furthermore, the
1-D1/4-D1 ratio correlates with coal vitrinite reflectance (Dzou et al. 1995 ; Hansen
et al. 2007 ; Stout and Emsbo-Mattingly 2008 ). As the coals mature, the value of the
1-D1/4-D1 increases, because the less stable 4-D1 decreases (Dzou et al. 1995 ).
The dimethyldibenzothiophenes, together with the methyldibenzothiophene dis-
tributions, may further assist in the identification of oils (Hegazi and Andersson
2007 ), or to distinguish between coal combustion and automobile emissions (Allan
1999 ; Marvin et al. 2000 and references therein). According to these authors, the
D1/D0 ratio is distinct for diesel emissions (1.6-2.9) and coal tars or coke oven
condensates (0.11-0.18). Similarly, the D2/D0 ratio ranges from 2.7 to 4.2 for diesel
vehicles, vs. a range of 0.03-0.04 for coal tars and coke oven condensates. Allan
( 1999 ) points out that coke oven emissions yield D2/D0 < 2.4. The D2/D0 ratio is
increased by biodegradation, solubilization and evaporation, whereas photo-
oxidation decreases it (Allan 1999 ).
Benzonaphthothiophenes are sometimes used for source discrimination tasks.
For example, the ratio of IP to benzo[ b ]naphtho[ 2 , 1 - d ]thiophene has been used to
distinguish vehicle emissions (<0.4) from urban heating sources (>0.9) in Gliwice,
Poland (Bylina et al. 2005 ). However, this ratio is insensitive to coke oven emis-
sions. Allan ( 1999 ) reported that the benzo[ b ]naphtho[ 2 , 1 - d ]thiophene/benzo[ b ]
naphtho[ 2 , 3 - d ]thiophene is characteristic for diesel emissions (>3.2), whereas coal
tar or coke oven emissions exhibit lower values of this ratio. For such sources, D0
and dibenzonaphthothiophene ratios are far superior to other PAH ratios (BeP/BaP,
ghi /BeP, BkF/BeP, ghi /BaP) (Allan 1999 ).

5.6 HMW Five- and Six-Ringed PAHs

5.6.1 Ratio of Benzo[ e ]pyrene to Benzo[ a ]pyrene

The benzo[ e ]pyrene/benzo[ a ]pyrene (BeP/BaP) ratio is indicative of aging particles
when >1, and has been used as a photodegradation indicator in atmospheric aerosols
(Okuda et al. 2002 ; Tan et al. 2009 ; Tobiszewski and Namiesnik 2012 ). The BeP/
BaP ratio is not affected by biodegradation and evaporation in sediments, tarballs,
tars and in creosote-contaminated sites (Costa and Sauer 2005 ; Stout et al. 2003 ;
Uhler and Emsbo-Mattingly 2006 ; Zakaria and Takada 2007 ).