Source Characterization of Polycyclic Aromatic Hydrocarbons by Using Their Molecular Indices: An Overview of Possibilities - Reviews of Environmental Contamination and Toxicology - page 116

good for distinguishing weathered crudes, whereas C2/P2 can be used to distinguish
crude from diesel, and 2-P1/1-P1 can be used to discriminate between fuel oils. For
coal PAHs, the phenanthrenic ratios (MPIs), the 1-D1/4-D1, and BbF/BkF correlate
with vitrinite reflectance (coal ranks). Unfortunately, little is known about the PAH
composition of coals, which is geographically very variable (Achten and Hofmann
2009 ; Stout and Emsbo-Mattingly 2008 ).
Three-ringed PAHs such as D n ( n = 1,2…), P1/A1, AY/AE, F0, and the two-
ringed N0 are useful for distinguishing coal-derived liquids such as unweathered
creosotes and coal tars, which do not follow the usual pyrogenic/petrogenic distri-
butions. Weathered creosotes are rich in benzofluoranthenes, BaA, benzopyrenes,
C0, FL0, PY0 (Fig. S28, Supporting Material). Ratios of four- or five-ringed
(methyl) PAHs such as C0/BaA, BbF/BkF, FP0/FP2 + FP3, may prove useful for
distinguishing (un)weathered creosote from background contamination and other
high-temperature processes.
Useful indicators of biomass combustion are alkylphenanthrenic indices such as
DMPs and retene (RET/C0, RET/PY1, RET/benzo[ b ]naphtho[ 2 , 1 - d ]thiophene etc.),
and PAH markers such as coronene. Of these, coronene is also a vehicle combustion
marker, as are five- to six-ringed PAHs such as BeP, ghi , PY0, and other LMW PAHs
(e.g., P1, F0, D0, benzonaphthothiophenes, etc.), which can assist in discriminating
automobile-related emissions from other combustion forms (wood, coal, etc.).
Perylene, even though not of anthropogenic origin, can help yield information as
to the source, depositional environment and the transport dynamics of the PAHs
before or during their deposition.
In summary, a full scan analysis (all suspected sources included) should include
the EPA16 parent PAHs (mostly pyrogenic discrimination), the five target alkylated
(PI and petroleum products), the fluoranthenes/pyrenes homologues (pyrogenic/
petrogenic discrimination), BeP (vehicle), PER (Biogenic), RET, and DMPs (bio-
mass/softwood). This “initial screening” yields a set of candidate substances to be
analyzed. A faster, cost-effective solution can narrow down the number of PAH
analytes, but it depends on the case in question.

6.2 What Are the Inherent Uncertainties in These Indicators

and How Does the Value of the Indicator Change After
Undergoing Biogeochemical Processes (i.e., Photochemical
Oxidation, Degradation, Volatilization, etc.) in the Aquatic
Environment?

PAH degradation, background contamination, mixing of multiple sources and simi-
larities between the PAH sources are functions of anthropogenic, environmental,
and geographic conditions that differentially affect all but a few PAH molecular
indices. It is possible to take these uncertainties into account by using suitable deg-
radation/weathering PAH ratios.