Particle and gaseous emissions from individual diesel and CNG buses 1IVL Swedish Environmental Research Institute, Gothenburg, Sweden
27 May 2013
2University of Gothenburg, Department of Chemistry and Molecular Biology, Atmospheric Science, Gothenburg, Sweden
Received: 14 July 2012 – Published in Atmos. Chem. Phys. Discuss.: 22 October 2012 Abstract. In this study size-resolved particle and gaseous emissions from 28
individual diesel-fuelled and 7 compressed natural gas (CNG)-fuelled buses,
selected from an in-use bus fleet, were characterised for real-world
dilution scenarios. The method used was based on using CO2 as a tracer
of exhaust gas dilution. The particles were sampled by using an extractive
sampling method and analysed with high time resolution instrumentation EEPS
(10 Hz) and CO2 with a non-dispersive infrared gas analyser (LI-840,
LI-COR Inc. 1 Hz). The gaseous constituents (CO, HC and NO) were measured by
using a remote sensing device (AccuScan RSD 3000, Environmental System
Products Inc.). Nitrogen oxides, NOx, were estimated from NO by using
default NO2/NOx ratios from the road vehicle emission model
HBEFA3.1. The buses studied were diesel-fuelled Euro III–V and CNG-fuelled
Enhanced Environmentally Friendly Vehicles (EEVs) with different
after-treatment, including selective catalytic reduction (SCR), exhaust gas
recirculation (EGR) and with and without diesel particulate filter (DPF).
The primary driving mode applied in this study was accelerating mode.
However, regarding the particle emissions also a constant speed mode was
analysed. The investigated CNG buses emitted on average a higher number of
particles but less mass compared to the diesel-fuelled buses. Emission
factors for number of particles (EFPN) were
EFPN, DPF = 4.4 ± 3.5 × 1014,
EFPN, no DPF = 2.1 ± 1.0 × 1015
and EFPN, CNG = 7.8 ± 5.7 ×1015 kg fuel−1.
In the accelerating mode, size-resolved emission factors (EFs) showed
unimodal number size distributions with peak diameters of 70–90 nm and 10 nm
for diesel and CNG buses, respectively. For the constant speed mode, bimodal
average number size distributions were obtained for the diesel buses with
peak modes of ~10 nm and ~60 nm.
Emission factors for NOx expressed as NO2 equivalents for the
diesel buses were on average 27 ± 7 g (kg fuel)−1 and for the CNG
buses 41 ± 26 g (kg fuel)−1. An anti-relationship between
EFNOx and EFPM was observed especially for buses with no DPF, and
there was a positive relationship between EFPM and EFCO.
Revised: 17 March 2013 – Accepted: 20 March 2013 – Published: 27 May 2013
Citation: Hallquist, Å. M., Jerksjö, M., Fallgren, H., Westerlund, J., and Sjödin, Å.: Particle and gaseous emissions from individual diesel and CNG buses, Atmos. Chem. Phys., 13, 5337-5350, doi:10.5194/acp-13-5337-2013, 2013.