Source Characterization of Polycyclic Aromatic Hydrocarbons by Using Their Molecular Indices: An Overview of Possibilities - Reviews of Environmental Contamination and Toxicology - page 66

motor vehicle exhausts. Indeno[ 1 , 2 , 3 - cd ]pyrene (IP) and benzo[ ghi ]perylene ( ghi )
are indicators (e.g., correlate with the total PAHs) of combustion sources and are
typical products of motor vehicle exhausts - although these HMW PAHs are not
transported far from their source (Boll et al. 2008 ; Larsen and Baker 2003 ; Ollivon
et al. 1999 ; Yunker et al. 2002 ). Ollivon et al. ( 1999 ) have suggested using benzo[ ghi ]
perylene and pyrene as tracers of vehicle emissions in river waters. Benz[ a ]anthra-
cene and chrysene are also considered to be automobile markers when other petro-
leum sources are excluded (Morillo et al. 2008b ; Yunker et al. 2002 ). Similarly,
particulate phase coronene in city centers may hypothetically be exclusively traffic-
related (Larsen and Baker 2003 ), especially at locations far from main point sources
of PAH emission (Bucheli et al. 2004 and references therein). Unlike the higher MW
alkylated PAHs (i.e., alkyl-fluoranthenes, -benz[ a ]anthracenes, -chrysenes, -pyrenes),
the alkylated LMW PAHs (i.e., alkyl phenanthrenes, alkyl anthracenes and alkyl
naphthalenes) are usually present in higher proportions than their parent PAHs in
diesel combustion soots and burn residues (Wang et al. 1999b ). The bell-shaped pro-
file of LMW PAHs in diesel combustion products accentuates the deviation from the
classical pyrogenic fingerprint, which prevails in higher MW PAHs (Fig. S17,
Supporting Material ; Sect. 2.1 ; Wang et al. 1999b ; Yunker et al. 2002 ). Higher MW
or sulfur PAHs such as coronene, BkF or benzo[ b ]naphtho[ 2 , 1 - d ]thiophene and
dibenzothiophenes have been proposed as markers of diesel emissions (Dobbins
et al. 2006 ; Larsen and Baker 2003 ; Marvin et al. 2000 ; Riddle et al. 2007 ; Wang
et al. 1999b ).
Compared with gasoline exhausts, diesel exhausts are said to be enriched in
phenanthrene, fluoranthene, pyrene and chrysene (Larsen and Baker 2003 ; Masclet
et al. 1986 ). Gasoline combustion produces patterns dominated by naphthalene and
HMW PAHs, such as benzo[ a ]pyrene and dibenz[ ah ]anthracene (Larsen and Baker
2003 ; Marr et al. 1999 ; Miguel et al. 1998 ; Valle et al. 2007 ). Instead, cyclopenta[ cd ]
pyrene and benzo[ ghi ]perylene have been proposed as markers for gasoline-fuel
combustion (Dzepina et al. 2007 ; Larsen and Baker 2003 ).
Motorcycles contribute significant amounts of PAHs to atmospheric environ-
ments in some locations, such as Southeast Asia. In other parts of the world (e.g.,
U.S.A. and Canada), motorcycle contribution to air PAHs is insignificant compared
to other traffic-related PAH emissions (Chien and Huang 2010 ; Oanh et al. 2013 ;
Valle et al. 2007 ). Two-stroke motorcycle exhausts have been reported to contain
higher amount of PAHs than four stroke or fuel injection motorcycles
(Boonyatumanond et al. 2007 ). Different factors such as motorcycle speed, engine
type and age affect the PAH patterns emitted (Chien and Huang 2010 ). Exhausts
from motor vehicles are transported far from point sources and contribute to diffuse
background levels.
The PAH concentrations decrease as the distance from traffic sources increases
(Boll et al. 2008 ). The typical gray particle color of automobile emissions makes the
particle-associated PAHs vulnerable to photodegradation (Dickhut et al. 2000 and
references therein). Furthermore, automotive emissions of PAHs depend on the fuel
and vehicle type and local traffic conditions (e.g., Geller et al. 2006 ; Lim et al. 2007 ;
Riddle et al. 2007 ).