posted on 2007-03-15, 00:00authored bySarah G. Riddle, Michael A. Robert, Chris A. Jakober, Michael P. Hannigan, Michael J. Kleeman
Size distributions of particulate hopanes, steranes, and
polycyclic aromatic hydrocarbons (PAHs) were measured
in the exhaust from four heavy-duty diesel vehicles
(HDDVs) operated under idle, creep, transient, and two high-speed driving modes. Particulate matter was collected
using a chassis dynamometer and a dilution sampling system
equipped with cascade impactors and filter samplers.
Samples were extracted using organic solvents and analyzed
using gas chromatography−mass spectrometry. Size
distributions of hopanes and steranes were functions of
engine load conditions and vehicle technology. Hopanes and
steranes peaked in size ranges larger than 0.18 μm
aerodynamic particle diameter under light load conditions
and less than 0.10 μm aerodynamic particle diameter
under heavier load conditions. The eight hopane size
distributions emitted from newer technology (>1998) vehicles
were unimodal while the four hopane size distributions
emitted from older technology vehicles (<1992) were bimodal.
Similar trends between older and newer vehicles were
not observed for sterane size distributions. The PAH
composition emitted from HDDVs was a function of driving
cycle and vehicle technology. Light driving cycles produced
quantifiable emissions of 3, 4, 5, and 6 ring PAHs (including
coronene). Heavier driving cycles produced only the 3 and
4 ring PAHs in quantifiable amounts. PM1.8 and PM0.1
source profiles constructed using the relative abundance
of hopanes and steranes to total organic carbon were
functions of vehicle load condition. Increasing load reduced
the relative abundance of motor oil tracers in the PM1.8
size fraction and increased the abundance of these tracers
in the PM0.1 size fraction. The relative abundances of
PAHs in the PM0.1 and PM1.8 size fractions emitted from
the oldest vehicle tested (1985 HDDV) were significantly
higher than for any other vehicle tested.