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mol). As petroleum matures, the DMP ratio decreases; softwood combustion how-
ever, is associated with high DMP values (Benner et al. 1995 ; Gogou et al. 2000 ;
Yunker et al. 2002 ).
Yunker et al. ( 2002 ) suggested that DMP > 0.7 indicates strong wood combustion
sources, and (Yan et al. 2005 , 2007 ) state that a DMP < 0.7 indicates that vehicle/
petroleum/fossil fuel or non-softwood emissions are dominant. Others (Lehndorff
and Schwark 2009 and references therein) have suggested that a ratio of DMP < 0.43
indicates vehicle emissions exclusively. Yunker et al. ( 2002 ) point out that DMP
ratios in the range of 0.45-0.7 may indicate marine or terrestrial oils, terrestrial
source rocks or even a mix of vehicle emissions and wood combustion. Thus, DMP
ratios in these ranges may imply multiple mixed sources.
The DMP ratio in aerial particulate matter was used to apportion softwood com-
bustion and motor vehicle emissions (Benner et al. 1995 ). It has also been used to
estimate the present and historic relative contributions of softwood, coal, and petro-
leum combustion sources to sediments (Yan et al. 2005 ; Yunker et al. 2002 ). In these
studies, the DMP ratio was used together with the fluoranthene to pyrene ratio.
However, for wood and coal combustion the DMP ratio is best used in conjunction
with the ratio of retene to chrysene (Yan et al. 2005 ). The DMP ratio has been used
together with the acenaphthylene to acenaphthene (AY/AE) ratio, which is a marker
for MGP tars, to distinguish coal soot from coal tar or other sources such as tires,
oil, or bitumen (Craig and Mauro 2012 ; Dupree and Ahrens 2007 ).
In sources other than softwood combustion, the DMP ratio has a low value and
should not be applied to distinguish petroleum or its combustion products, particu-
larly in sediments with background contamination (Bogdal et al. 2011 ; Yunker et al.
2002 ). Biodegradation increases the DMP ratio (Jimenez et al. 2006 and references
therein). The DMP and RET/C0 ratios may also be compromised by hardwood emis-
sions, which produce lower ratios than softwood emissions (Yan et al. 2005 ).
Therefore, DMP-based source apportionment may be inaccurate in areas affected by
multiple combustion sources (Elmquist et al. 2007 ; Mandalakis et al. 2004 ). Yan et al.
( 2005 ) have argued that 7,9-dimethylphenanthrene may be used instead of 2,6 DMP
to apportion PAHs from fresh bituminous coal and brown-coal smoke. These two
substances are present in similar amounts in bituminous sources, although softwood
combustion emissions contain much greater amounts of 1,7 DMP than 1,6 DMP.
5.4
Four-Ringed PAHs
5.4.1
The Ratio of Fluoranthene to Pyrene
Similar to the P0/A0 ratio, the fluoranthene to pyrene (FL0/PY0) ratio correlates
with the temperature of formation (e.g., Budzinski et al. 1997 ). Thermodynamically,
fluoranthene is less stable than its isomer pyrene (Yan et al. 2005 ). FL0 is less
favored than PY0 under fossil fuel formation conditions (Iqbal et al. 2008 ). As a
result, FL0/PY0 < 1 for petrogenic products, except for certain coals, crudes and
diesels (Fig. 12 ).
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