Supplemental Information
Comparison of vehicle exhaust particle size distributions measured by
SMPS and EEPS during steady-state conditions
Jian Xuea,b, Yang Lia,b, Xiaoliang Wangc, Thomas D. Durbina, Kent C. Johnsona, Georgios
Karavalakis, Akua Asa-Awukua, Mark Villelaa, David Quirosd, Shaohua Hud, Tao Huaid,
Alberto Ayalad and Heejung S. Junga,b,*
aCenter
for Environmental Research and Technology (CE-CERT), Bourns College of Engineering,
University of California, Riverside, Riverside, California, USA
b
Department of Mechanical Engineering, University of California Riverside, Riverside, California, USA
cDesert
d California
Research Institute, Reno, Nevada, USA
Air Resources Board (CARB), 1001 I Street, Sacramento, California, USA
This Supplemental Information contains the following information:
Section S1. Variations in particle mass emissions due to uncertainties in particle density for
the nucleation mode.
Section S2. Size distribution of SMPS and EEPS with Mazda 3 GDI at 30 mph.
Table S1. Particle mass emission estimation using two different particle effective density
profiles.
Figure S1. Schematic of the test setup.
Figure S2. Particle mass distribution by EEPS and SMPS with a GDI vehicle at steady state
speed of 30 mph.
Section S1: Variations in particle mass emissions due to uncertainties in particle density
for the nucleation mode.
In the main text, a constant density of hydrated sulfuric acid (1.46 g/cm3) was assumed for dp
< 30 nm, based on data presented by Zheng et al. (2012). However, this particle density did
not consider the condensation of organics and growth of nucleation-mode particles, which
may be significant in some engine operation conditions and fuels. Therefore, we assumed a
different particle density somewhat arbitrarily to assess the extent of the influence of particle
effective density on the total suspended particle mass. For dp >30 nm, the second density
profile (denoted as density2) share the same values of particle effective density with the
primary density profile (denoted as density1) in the main text. However, dp < 30 nm, the soot
effective density of 1.2 g/cm3 approximated by Maricq and Xu (2004) was applied. The IPSD
mass emission rates calculated with two sets of particle effective densities were calculated
and listed in Table S1.
The most significant change (~15%) was observed with the emissions of TDI vehicle
operated at 60 mph and 4% load based on SMPS measured particle size distributions. This is
expected because 99.9% the measured particles number was from nucleation mode particles.
For the emissions from the diesel generator, the GDI vehicle at 30 mph, and PFI vehicle at 25
mph, only very small changes in MIPSD were observed (varying from 0-0.8%). For the
emissions with the vehicle at 60 mph and 2% load, a change of 7% was observed as shown in
Table S1.
Section S2: GDI vehicles at 30 mph (Overlapping bi-modal distribution)
Figure S2a compares particle size distributions measured by the EEPS and SMPS for the GDI
vehicle operated at 30 mph using the EEPS Default and Soot Matrices. Larger uncertainties
observed during this condition compared to the 60-mph test condition. The SMPS reported a
bimodal size distribution with GMDs of 8 and 52 nm for the nucleation and accumulation
modes, respectively. Based on the relative contributions of the bimodal lognormal fit, the
nucleation mode contributed 82% of total particle number, a substantially larger fraction than
the nucleation mode observed during the test of the diesel generator using bio-fuel (12%). It
is also larger than the fraction of the nucleation mode observed during the test of the same
GDI vehicle at a higher speed of 60 mph (54%). The EEPS Default Matrix reported a slightly
lower particle size distributions for the accumulation mode particles compared to SMPS
(GSD= 1.84 vs. GSD=1.97), as shown in Figure S2 and Table 3. Both the EEPS Default and
Soot Matrices reported GMDs of accumulation mode much different from the of the
reference SMPS measurement.
The total particle number emission rates measured with the EEPS Default Matrix was 2.28 ±
0.88 × 1011 /mile, 28% lower than that estimated by the SMPS (3.18 ± 0.26 × 1011 /mile).
MIPSD estimated by the EEPS Default Matrix was 0.012 ± 0.004 mg/mile, 33% lower than
that estimated by the SMPS (0.018 ± 0.006 mg/mile). These results indicate that the EEPS
Default Matrix underestimates both particle number and mass emissions relative to the SMPS
when measuring light-duty GDI emissions at a lower speed. It is very consistent with the
results using the same vehicle under higher speed of 60 mph. It is also consistent very well
with our previous evaluation of the IPSD method over the transient FTP cycle1.
When the EEPS Soot Matrix was applied, the agreement in particle sizing given by the two
instruments was improved for nucleation particles and particles larger than 100 nm. Total
particle number emission rate was estimated to be 3.46 ± 1.32 × 1011 /mile, ~9% higher than
those measured by the SMPS. The mass (MIPSD) emission rate was estimated to be 0.016 ±
0.006 mg/mile, agreeing well with the emission rate estimated with SMPS (0.018 ± 0.006
mg/mile), but still underestimating the emissions in the mass distribution by around 12%.
Compared to the comparison of the emissions of this vehicle operating at 60 mph and a 2%
simulated road grade, the agreement of the EEPS Soot Matrix is inferior.
The Soot Matrix
showed some difficulty reproducing exact bimodality the reference measured showed. We
speculate this might be due to difference in sizing resolution between the EEPS and SMPS.
This could suggest that for a given characteristic of aerosol especially with bimodal size
distirbutions, there may be a limitation of the performance of the EEPS Soot Matrix.
Nevertheless, over a range of particle concentrations elicited by the light-duty GDI vehicle,
particle number and mass distributions agreed with the EEPS Soot Matrix within a reasonable
margin.
Table S1. Particle mass emission estimation using two different
particle effective density profiles.
SMPS
EEPS Default
EEPS Soot
Tests
Density1
Density2
Density1
Density2
Density1
Density2
Diesel-Reg (mg/bhp-hr)
672±28
670±28
417±37
417±37
630±62
628±62
Diesel-Bio (mg/bhp-hr)
236±6
234±6
162±10
160±10
240±17
238±16
GDI-60 (mg/mile)
0.15±0.03
0.14±0.03
0.10±0.02
0.10±0.02
0.15±0.03
0.15±0.03
GDI-30 (mg/mile)
0.018±0.006
0.018±0.006
0.012±0.004
0.011±0.004
0.016±0.006
0.016±0.006
TDI-60 (mg/mile)
1.17±0.14
1.00±0.12
0.12±0.01
0.12±0.01
0.17±0.01
0.17±0.01
PFI-25 (mg/mile)
0.46±0.32
0.46±0.31
0.34±0.38
0.34±0.38
0.52±0.56
0.52±0.56
HEPA filtered
laboratory air
Pump
CVS Sampling System –
1st
Dilution Tunnel
Mini dilution tunnel
EEPS
SMPS
Other
instument
Figure S1. Schematic of the test setup. Other instruments include a series of gas analyzers
that measure the concentrations of CO, CO2, NOx and etc.
1.E+05
1.E+10
(a)
1.E+08
1.E+03
1.E+07
1.E+02
dN/dlogDp (# mile -1)
dN/dlogDp (# cm-3)
1.E+09
1.E+04
1.E+06
1.E+01
1.E+05
1
10
1.E-05
SMPS
1.E+05
100
Dp (nm)
EEPS-Default
(b)
SMPS Nucl. fitted
1000
1.40E+02
EEPS-Soot
1.E+10
SMPS Accu. fitted
dM/dlogDp (μg cm-3)
dN/dlogDp (# cm-3)
(μg
dM/dlogDp
mile-1)-1)
dN/dlogDp (#
mile
1.E+09
1.40E+01
1.E-06
1.E+04
1.E+08
1.E-07
1.E+03
1.40E+00
1.E+07
1.E-08
1.E+02
1.40E-01
1.E+06
1.E-09
1.E+01
1 1
10 10
SMPS
SMPS
SMPS Nucl. fitted
100100
Dp
(nm)
Dp (nm)
EEPS-Default
EEPS-Default
SMPS Accu. fitted
1.40E-02
1.E+05
1000
1000
EEPS-Soot
EEPS-Soot
Figure. S2 (a) Particle size distribution by EEPS and SMPS with a GDI vehicle at a speed of
30 mi/hr and 0% road grade. Black solid and dashed lines present lognormal fitted size
distribution of nucleation and accumulation mode particles respectively by SMPS. The same
results corrected by dilution ratio of sampling system were presented on the right y-axis. (b)
Particle mass distribution by EEPS and SMPS.
References:
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Measure Light-Duty Vehicle Particulate Matter Emissions at Levels below One Milligram per Mile (1
mg/mile), SAE Tech. Pap. 2014-01-1571,
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