We assessed the emissions response
of a fleet of seven light-duty
gasoline vehicles for gasoline fuel aromatic content while operating
over the LA92 driving cycle. The test fleet consisted of model year
2012 vehicles equipped with spark-ignition (SI) and either port fuel
injection (PFI) or direct injection (DI) technology. Three gasoline
fuels were blended to meet a range of total aromatics targets (15%,
25%, and 35% by volume) while holding other fuel properties relatively
constant within specified ranges, and a fourth fuel was formulated
to meet a 35% by volume total aromatics target but with a higher octane
number. Our results showed statistically significant increases in
carbon monoxide, nonmethane hydrocarbon, particulate matter (PM) mass,
particle number, and black carbon emissions with increasing aromatics
content for all seven vehicles tested. Only one vehicle showed a statistically
significant increase in total hydrocarbon emissions. The monoaromatic
hydrocarbon species that were evaluated showed increases with increasing
aromatic content in the fuel. Changes in fuel composition had no statistically
significant effect on the emissions of nitrogen oxides (NO<sub><i>x</i></sub>), formaldehyde, or acetaldehyde. A good correlation
was also found between the PM index and PM mass and number emissions
for all vehicle/fuel combinations with the total aromatics group being
a significant contributor to the total PM index followed by naphthalenes
and indenes
