This paper reports mass measurements, size distributions,
and the transient response of tailpipe particulate
emissions from 21 recent model gasoline vehicles.
Transient measurements are made for the FTP drive cycle
(and limited ECE tests) using a scanning mobility particle
sizer and an electrical low-pressure impactor. The particles
emitted in vehicle exhaust have diameters in the 10-300
nm diameter range, with a mean diameter of about 60 nm.
Particle emissions during the drive cycles occur as
narrow peaks that correlate with vehicle acceleration.
Cold start emissions generally outweigh those from a hot
start by more than a factor of 3. Particulate mass deduced
from the transient distributions agrees semiquantitatively
with gravimetric measurements. Tailpipe particulate emissions
from the recent model gasoline vehicles tested are very
low, with mass emission rates ranging downward from 7 mg/
mi for a light-duty truck during the cold start phase of
the FTP drive cycle to e0.1 mg/mi during phase 2 for nearly
half of the test vehicles. Three high-mileage (>100 K mi)
test vehicles exhibited similarly low particulate emission rates.
The FTP-weighted 3-bag average is under 2 mg/mi for
all the conventional gasoline vehicles tested.