Diesel Bus Emissions Measured in a Tunnel Study

The emission factors of a bus fleet consisting of
approximately 300 diesel-powered buses were measured
in a tunnel study under well-controlled conditions during a
2-d monitoring campaign in Brisbane. Particle number
and mass concentration levels of submicrometer particles
and PM2.5 were monitored by SMPS and DustTrak
instruments at the tunnel's entrance and exit, respectively.
Correlation between DustTrak and TEOM response to
diesel emissions was assessed, and the DustTrak results
were recalculated into TEOM equivalent data. The mean value
of the number and mass emission factors was (3.11±2.41)
× 1014 particles km-1 for submicrometer particles and
583±451 mg km-1 for PM2.5 (DustTrak), respectively. TEOM
PM2.5 equivalent emission factor was 267 ± 207 mg
km-1. The results are in good agreement with the emission
factors determined from steady-state dynamometer
testing of 12 buses from the same Brisbane City bus fleet.
The results indicate that when carefully designed, both
approaches, the dynamometer and on-road studies, can
provide comparable results, applicable for the assessment
of the effect of traffic emissions on airborne particle
pollution. A brief overview of emission factors determined
from other on-road and dynamometer studies reported
in the literature as well as with the regulatory values used
for the vehicle emission inventory assessment is presented
and compared with the results obtained in this study.