Temperature and Driving Cycle Significantly Affect Carbonaceous Gas and Particle Matter Emissions from Diesel Trucks

The present study
examines the effects of fuel [an ultralow sulfur
diesel (ULSD) versus a 20% v/v soy-based biodiesel–80% v/v
petroleum blend (B20)], temperature, load, vehicle, driving cycle,
and active regeneration technology on gas- and particle-phase carbon
emissions from light and medium heavy-duty diesel vehicles (L/MHDDV).
The study is performed using chassis dynamometer facilities that support
low-temperature operation (−6.7 °C versus 21.7 °C)
and heavy loads up to 12 000 kg. Organic and elemental carbon
(OC-EC) composition of aerosol particles is determined using a thermal-optical
technique. Gas- and particle-phase semivolatile organic compound (SVOC)
emissions collected using traditional filter and polyurethane foam
sampling media are analyzed using advanced gas chromatograpy/mass
spectrometry methods. Study-wide OC and EC emissions are 0.735 and
0.733 mg/km, on average. The emissions factors for diesel vehicles
vary widely, and use of a catalyzed diesel particle filter (CDPF)
device generally mutes the carbon particle emissions in the exhaust,
which contains ∼90% w/w gas-phase matter. Interestingly, replacing
ULSD with B20 did not significantly influence SVOC emissions, for
which sums range from 0.030 to 9.4 mg/km for the L/MHDDVs. However,
both low temperature and vehicle cold-starts significantly increase
SVOCs in the exhaust. Real-time particle measurements indicate vehicle
regeneration technology did influence emissions, although regeneration
effects went unresolved using bulk chemistry techniques. A multistudy
comparison of the toxic particle-phase polycyclic aromatic hydrocarbons
(PAHs; molecular weight (MW) ≥ 252 amu) in diesel exhaust indicates
emission factors that span up to 8 orders of magnitude over the past
several decades. This study observes conditions under which PAH compounds
with MW ≥ 252 amu appear in diesel particles downstream of
the CDPF and can even reach low-end concentrations reported earlier
for much larger HDDVs with poorly controlled exhaust streams. This
rare observation suggests that analysis of PAHs in particles emitted
from modern L/MHDDVs may be more complex than recognized previously.