Source Characterization of Polycyclic Aromatic Hydrocarbons by Using Their Molecular Indices: An Overview of Possibilities - Reviews of Environmental Contamination and Toxicology - page 96

incorporated uncombusted into diesel soots, retaining the bell-shaped distribution
(Fig. 4 and Fig. S16, Supporting Material), which readily modifies to a
PAH0 < PAH1 < PAH2 < PAH3 profile during weathering. Furthermore, the ratio of
alkylated chrysenes to the five target alkylated PAH homologues is significantly
higher in diesel soots (0.1-0.2) or in diesel burn residues than in diesel fuel (0.001)
or other weathered fuels (Wang et al. 1999b ).
Urban background or pyrogenic impact on sediments can be deduced from high
ratios of chrysene to dimethylchrysenes (i.e., predominance of non-alkylated parent
PAHs over their dimethyl- or ethyl-alkylated equivalents) (Stout et al. 2004 ). This
C0/C2 ratio is minimally affected by degradation, can indicate pyrogenic origin if
higher than 1 (Battelle Memorial Institute et al. 2003 ), and can be used to distin-
guish between different pyrogenic sources (Roush and Mauro 2009 ). Similarly,
Wang et al. ( 2001 ) used the relative distribution of the highly degradation-resistant
alkyl (C0 to C3) chrysene series to apportion sources by using mass balance
equations.

BC
CC

0
23

The ratio is a measure of the alkylation (Stout et al. 2003 ) and can be

+

used to determine pyrogenic or petrogenic origin. For example, the contribution of
a petroleum component (lubricating oil) to urban background enabled Stout et al.
( 2003 ) to distinguish creosote from urban background by using the BC0/C2 + C3
ratio. The measured values for the BC0/C2 + C3 ratio given by Stout ( 2007 ) for
contributions to sediments are 0.11-0.12 for crude, 0.28-0.27 for petrogenic and
4.11-7.86 for pyrogenic. In coal tars, the biodegradability of the BC0/C2 + C3 ratio
is moderate and its evaporability is negligible (Douglas et al. 2007a ; Uhler and
Emsbo-Mattingly 2006 ). Saha et al. ( 2009 ) suggested that the BC0/BC1 ratio can be
used to distinguish pyrogenic (>1) from petrogenic sources. Costa et al. ( 2004 ) used
the C n /FP n double ratio plot ( n = 1, 2) to distinguish MGP tars from background
pyrogenic contamination.
Several weathering ratios that use chrysenes have been reported. Degradation
increases the ratios C2/P2 and C3/P3 at a relatively constant rate (Barakat et al.
2001 ; Bence et al. 1996 ). Additionally, these ratios can assist in discriminating dis-
tillates such as diesel (when alkylated chrysenes are absent the ratios approach zero)
from unweathered crude oil (Bence et al. 1996 ). Similarly, the ratio of the C2-C4
alkylchrysenes to the P2-P4 alkylphenanthrenes increases as the weathering pro-
ceeds, because phenanthrenes are more soluble in water and are thus removed from
the oil faster (Page et al. 2003 ). In general, ratios of chrysenes to the more degrad-
able two- and three-ringed PAHs can be used to ascertain the weathering state of
sediments (partly because of the low solubility of chrysenes in water) (Kim et al.
2008 ; Page et al. 1999 ). Such ratios are called weathering ratios (weathering and
biodegradation greatly affect them). Weathering-sensitive ratios are usually
combined with ratios that are unaffected by weathering, to resolve multiple sources
and the extent of weathering (Barakat et al. 2001 ).