vehicle generated nanoparticles are not an artifact! d. b. kittelson, w.f. watts, and j.p. johnson...
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Vehicle generated nanoparticles are not an artifact!
D. B. Kittelson, W.F. Watts, and J.P. JohnsonCenter for Diesel Research
University of Minnesota
8th CONFERENCE ON ENVIRONMENTAL SCIENCE AND TECHNOLOGY
PARTICULATES WORKSHOP
11th SEPTEMBER 2003
Lemnos Island, GREECE
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Outline
• Size and composition
• On-road measurements– On-road measurements in mixed urban traffic
– Weekday/weekend determinations of on-road emission factors
– On-road characterization of post 2007 system
• Conclusions
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Typical Engine Exhaust Particle Size Distributions, Number, Surface Area, and Mass Weightings Are Shown
0
0.05
0.1
0.15
0.2
0.25
1 10 100 1,000 10,000
Diameter (nm)
No
rmal
ized
Co
nce
ntr
atio
n (
1/C
tota
l)dC
/dlo
gD
p
Number Surface Mass
Fine ParticlesDp < 2.5 m
Ultrafine ParticlesDp < 100 nm
NanoparticlesDp < 50 nm
Nuclei Mode - Usually forms from volatile precursors as exhaust dilutes and cools
Accumulation Mode - Usually consists of carbonaceous agglomerates and adsorbed material
Coarse Mode - Usually consists of reentrained accumulation mode particles, crankcase fumes
PM10Dp < 10 m
In some cases this mode may consist of very small particles below the range of conventional instruments, Dp < 10 nm
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Nuclei mode (~3 to 30 nm diameter)
• The nuclei mode contains most of the particle number• Nuclei mode particles form mainly from volatile precursors1
– The nuclei mode typically consists mainly of heavy hydrocarbons, mainly from lubricating oil, and sulfates
– Although although the mode is mainly hydrocarbon, its formation is facilitated by sulfur in the fuel
– Its formation is very dependent on dilution conditions, especially dilution rate and dilution air temperature
– Its formation is favored by low solid carbon and high precursor concentration
• Solid nuclei mode particles may form from metals in the lube oil or fuel– Formed from oil under engine conditions that lead to little solid carbon
formation. – Formed from fuel when metallic additives or high metal fuels are used.
• A volatile nuclei mode will be all that is left when solid particles are removed by exhaust filtration
1 - Sakurai, Hiromu, Herbert J. Tobias, Kihong Park, Darrick Zarling, Kenneth S. Docherty, David B. Kittelson, Peter H. McMurry, and Paul J. Ziemann, 2002. “On-Line Measurements of Diesel Nanoparticle Composition, Volatility, and Hygroscopicity,” Submitted to Atmospheric Environment
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Accumulation mode (~30 to 500 nm)
• The accumulation mode contains most of the particle mass and “soot”• Consists primarily of carbonaceous agglomerates and adsorbed OC• Particles in this mode are strongly light absorbing and may influence
global warming• Most of the lubricating oil ash is found in this mode – this enhances soot
oxidation in exhaust filters but eventually plugs them• Density of accumulation mode particles decreases with increasing size1
– Fractal like behavior– Low densities cause size to be underestimated by some methods
• Accumulation mode particles have been reduced sharply by better engine technology and will be eliminated by efficient filtration
1 - Park, Kihong, Feng Cao, David B. Kittelson, and Peter H. McMurry, 2002. “Relationship Between Particle Mass and Mobility, and Between Aerodynamic and Mobility Size Distributions for Diesel Exhaust Particles,” Submitted to Environmental Science & Technology
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U of M Mobile Laboratory built to study formation of nanoparticles in the atmosphere for the CRC E-43 project
• Instruments (primary instruments highlighted in blue)– SMPS to size particles in 9 to 300
nm size range– ELPI to size particles in 30 to 2500
nm size range– CPC to count all particles larger
than 3 nm– Diffusion Charger to measure total
submicron particle surface area– Epiphaniometer to measure total
submicron particle surface area– PAS to measure total submicron
surface bound PAH equivalent– CO2 , CO, and NO analyzers for
gas and dilution ratio determinations
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On-highway measurements made on urban freeways in Minnesota show a large nuclei mode even in the absence of significant Diesel traffic
• Traffic speed has at least as much influence on the size of the nuclei mode as the presence of Diesel traffic
• Particle number increases and size decreases as traffic speed increases• Particle volume (mass) is higher under low speed congested conditions• It appears that slow moving congested traffic leads to storage of volatile materials
in the exhaust system• As vehicles speed up the exhaust system heats leading to the release of the
materials which subsequently form nanoparticles
0
100000
200000
300000
400000
500000
1 10 100 1000
Midpoint Diameter (nm)
dN
/dlo
gDp
(p
art.
/cm
3)
Diesel=Y, MPH >=0 <=10 Diesel=Y, MPH >10 <50 Diesel=Y, MPH >=50
Diesel=N, MPH >=0 <=10 Diesel=N, MPH >10 <50 Diesel=N, MPH >=50
0.0E+00
1.0E+04
2.0E+04
3.0E+04
4.0E+04
5.0E+04
6.0E+04
0 10 20 30 40 50 60
Speed, mph
N/V
(pa
rt./ m
3 )
0
6
12
18
24
30
36
DG
N (
nm)
N/V
DGN
N/V of 1 part./m3 =1012 part./gm for spherical unit density particles
Diesel
No Diesel
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Nuclei Mode Decays Rapidly Downwind of Roadways• Modeling (Capaldo and
Pandis, 2001) indicates– For typical urban conditions,
characteristic times and transit distances for 90 % reduction of ultrafine concentrations are on the order of a few minutes and 100-1000 m, respectively.
– For a given wind speed, ultrafine particles are expected to survive and travel a factor of ten greater distances in a rural flat area as compared to an urban downtown location.
• Mobile particle sources will influence the aerosol particle number concentrations mainly near roadways.
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Nanoparticles Are Composed of Mainly Volatile Material
1.0E+02
1.0E+03
1.0E+04
1.0E+05
1.0E+06
1 10 100 1000
Diameter, nm
dN/d
logD
p, p
art/
cm3
12 Sept 02 UMN SMPS, N=25516 Sept 02 UMN SMPS, N=23312 Sept 02 TDSMPS, N=25616 Sept 02 TDSMPS, N=233
SMPS - no thermal denuder
SMPS - thermal denuder at 300o C
Large Reduction in Nuclei Mode
87-95% Reduction
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On-Road Characterization of Real World Fleets: Weekday / Weekend On-Highway Apportionment Experiments
• Summertime urban freeway measurements
• Over-the-road aerosol, corrected for the background is contributed by vehicles in proportion to their traffic volume.
• Measuring traffic volumes and aerosol concentrations on days with differing SI to Diesel ratios gives a system of equations that can be solved for average Diesel and SI contribution on a per unit traffic volume basis
• Presented on a fuel specific (per kg of fuel) basis
• Principal uncertainties are in traffic counts and background corrections
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Diesel/SI Ratio By Route And Day
Ratio Diesel/SI Separated by Route and Day
0.00
0.01
0.02
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0.04
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0.06
0.07
0.08
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0.13
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62 & 169 (red) 100 & 169 (blue) 94 & 494 (green)
Route
Rat
io D
iese
l/SI
Sunday May 12, 2002
Tuesday May 21, 2002
Route selected
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Average Weekend vs. Weekday Size Distributions
SMPS Average Size Distributions - Sunday vs. Weekday + MnDOT
1.0E+02
1.0E+03
1.0E+04
1.0E+05
1.0E+06
1 10 100 1000
Diameter, nm
dN
/dlo
gD
p,
part
/cm
3
MnDOT, N = 457
Week Day Average, N = 605
Sunday Average, N = 189
DOE data uncorrected for background and particle lossesMnDOT data uncorrected for particle losses
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Diesel and SI Apportioned Size Distributions on a Fuel Specific Basis
Fuel Specific Contribution to On-Highway Aerosol by Vehicle Type
1.0E+10
1.0E+11
1.0E+12
1.0E+13
1.0E+14
1.0E+15
1.0E+16
1.0E+17
1 10 100 1000
Dp (nm)
dN
/dlo
gD
p p
er k
g o
f fu
el b
urn
ed,
pa
rt/c
m3 /k
g
SI, On-Hwy
Diesel, On-Hwy
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Diesel On-Highway Compared to CRC E-43 Fleet Average On a Fuel Specific Basis
Fuel-Specific Comparison of On-Highway Diesels to CRC E-43 Diesel Fleet Averages for Various Conditions
1.0E+10
1.0E+11
1.0E+12
1.0E+13
1.0E+14
1.0E+15
1.0E+16
1.0E+17
1 10 100 1000
Dp (nm)
dN
/dlo
gD
p p
er k
g o
f fu
el b
urn
ed,
pa
rt/c
m3 /k
g
Diesel, On-Hwy
CRC E-43, Diesel, Acceleration
CRC E-43, Diesel, 60 Cruise
CRC E-43, Diesel, 55 Cruise
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Source Apportioned Highway Cruise SI Fleet Average Compared to Chase and Chassis Dyno Measurements
Fuel-Specific Comparison of On-Highway SI Vehicles to SI Fleet Averages, Highway Conditions for both CVS and Chase Testing
1.0E+10
1.0E+11
1.0E+12
1.0E+13
1.0E+14
1.0E+15
1.0E+16
1.0E+17
1 10 100 1000
Dp (nm)
dN
/dlo
gDp
per
kg
of f
uel
bu
rned
, p
art/
cm3 /kg
SI, On-Hwy
SI, Acceleration, Chase
SI, 70 Cruise, CVS
SI, 65 Cruise, CVS
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• The proposed (by Swiss) EU standard of 1011 particles/km corresponds to about 2 x 1012 particles/kg fuel of solid particles
• If we assume all particles above 30 nm are solid our fleet emission factors are 5 x 1014 and 9 x 1013 particles/kg fuel for Diesel and SI, respectively
• These are a snapshot of Minnesota urban freeway fleets – more work is needed
Fuel Specific Emissions – Diesel and SI Summertime Highway Cruise
Mean SDOM Mean SDOM Mean SDOM Mean SDOMDiesel 1.34E+16 1.86E+15 2.13E+15 3.04E+14 3.15E+12 6.15E+11 1.45E+13 2.15E+12
SI 7.10E+15 1.55E+15 3.88E+14 6.11E+13 1.77E+11 3.91E+10 9.41E+11 1.52E+11
Mean SDOM Mean SDOM Mean SDOM Mean SDOMDiesel 2.91E+12 4.04E+11 6.21E+11 1.40E+11 22.7 1.7 195.7 12.1
SI 5.69E+11 1.26E+11 1.44E+10 4.44E+09 19.3 0.7 104.0 24.3
Mean SDOM Mean SDOM Mean SDOMDiesel 3.44E+03 7.76E+02 0.76 0.13 0.008 0.002
SI 2.70E+04 7.69E+03 0.77 0.09 0.059 0.017
Apportioned Source
Apportioned Source
PAS (fA/kg)
N/V Ratio
CPC (part/kg) SMPS Number (part/kg) DC (µm2/kg)Apportioned Source
N30/N Ratio
SMPS Active Surface (µm2/kg)
V30/V Ratio
DGN (nm) DGV (nm)SMPS Volume (µm3/kg)
Dp > 3 nm Dp > 10 nm
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On-road characterization of post a 2007 aftertreatment system – we sniff our own exhaust plume
Driver side sample point
Passenger side sample point
Background sample point
Stacks
Stacks
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On road tests of particle filtration device – volume (mass) distributions
0.0E+00
5.0E+00
1.0E+01
1.5E+01
2.0E+01
2.5E+01
3.0E+01
3.5E+01
4.0E+01
1 10 100 1000
Dp, nm
dVdl
ogD
p,
m3 /c
m3
Engine out with low S oil
Filter with standard oil, August
Filter with standard oil, October
All tests done with 15 ppm S fuel (post 2006) with standard or low sulfur lubricant
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On-road nanoparticle measurements for real world fleets
• On-road nanoparticles are real• On-road submicron on-road aerosols are found in two principal size modes
– A nuclei mode in the nanoparticle range containing most of the particle number– An accumulation mode in the ultrafine and fine range containing most of the particle
mass.
• Most nuclei mode particles are volatile and very sensitive to dilution conditions, both on-road and in the laboratory
• Both Diesel and SI engines are important contributors to the on-road aerosol– Both engine types produce significant nuclei mode (nanoparticles)– SI particles are usually smaller– SI particle emissions are much more load dependent
• On-road measurements with post 2007 systems may show large nuclei mode with some systems
• More work should be done to determine nanoparticle formation with new engines and fuels and for a range of ambient and operating conditions
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Acknowledgements
• We have had help from many collaborators– In the Center for Diesel Research
• Feng Cao, Marcus Drayton, Jason Johnson, Hee Jung Jung, Duane Paulsen, Winthrop Watts, Robert Waytulonis, Qiang Wei, Darrick Zarling
– At Paul Scherrer Institute• Nick Bukowiecki, Urs Baltensperger, Adelheid Kasper
• And many sponsors– Coordinating Research Council, U.S. Office of Heavy Vehicle
Technologies, Engine Manufacturers Association, Southcoast Air Quality Management District, California Air Resources Board, BP/Amoco, Castrol, Corning, Cummins, Caterpillar, Perkins, and Volvo.