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D. Kittelson 11 University Minnesota Minneapolis USA Diesel Aerosol sampling in the atmosphere
DIESEL AEROSOL SAMPLING IN THE ATMOSPHERE
David Kittelson, Jason Johnson, and Winthrop WattsCenter for Diesel Research
University of Minnesota
4th ETH Conference on Nanoparticle MeasurementZürich, Switzerland
7-9 August, 2000
This work is based in part on preliminary results from CRC E-43 Project, “Diesel Aerosol Sampling Methodology”
• Prime Contractor: University of Minnesota• Subcontractors: West Virginia University, Paul Scherrer
Institute, Carnegie Mellon University, Tampere University• Sponsors: Coordinating Research Council and the National
Renewable Energy Laboratory with co-sponsorship from the Engine Manufacturers Association, the Southcoast Air Quality Management District, the California Air Resources Board, Cummins, Caterpillar, and Volvo.
• Other information is based on work sponsored by Perkins Engine Company and Cummins Diesel
Typical Diesel Particle Size Distribution - Log Scale
Typical Engine Exhaust Size DistributionBoth Mass and Number Weightings are Shown
0.00001
0.0001
0.001
0.01
0.1
1
0.001 0.010 0.100 1.000 10.000
Diameter (µµµµm)
Nor
mal
ized
Con
cent
ratio
n, d
C/C
tota
l/dlo
gDp
Mass Weighting Number Weighting
Fine ParticlesDp < 2.5 µm
Ultrafine ParticlesDp < 100 nm
NanoparticlesDp < 50 nm
NucleiMode
AccumulationMode
CoarseMode
PM10Dp < 10 µm
Background
• Concerns about particle size– New ambient standards on fine particles– Special concerns about ultrafine and nanoparticles– Indications that reductions in mass emissions may increase
number emissions
• Difficulties associated with measurement of ultrafineand nanoparticles– Often more than 90% of particle number are formed during
exhaust dilution– Semivolatile nanoparticle concentrations may be changed
by orders of magnitude during sampling and dilution
Influence of Residence Time onNumber Weighted Size Distributions
1.00E+05
1.00E+06
1.00E+07
1.00E+08
1.00E+09
1.00E+10
1 10 100 1000Dp (nm)
DN
/DLo
g D
p (P
art./
cm³)
Residence time = 1000 ms 100 ms 230 ms
Tdilution = 32 °C, Primary DR ~ 12
1600 rpm, 50% load
Goals and Objectives of the E-43 Program
• Measure on-road particle size distributions (number, volume, surface area) in the exhaust plume of heavy-duty diesel vehicles.
• Attempt to reproduce these results under laboratory conditions (chassis dynamometer, wind tunnel, engine dynamometer)
• Model atmospheric aging and dispersion of freshly emitted diesel aerosols
• Determine size fractionated chemical composition of diesel particulate matter collected in laboratory and in wind tunnel
In Order to Understand the Environmental Impact of Nanoparticles We Must Study Their Formation in the Atmosphere. This is the U of M E-43 Mobile Laboratory.
University of Minnesota, E-43, Mobile Aerosol Laboratory during a Roadway Chase Experiment
Principal Instruments Used in MEL for Initial Chase Experiments
• 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 and NO analyzers for for dilution ratio
determinations
Typical On Road Size Distributions - 55 mph
6 October Cruise CA light load ISM Truck
1.00E+03
1.00E+04
1.00E+05
1.00E+06
1 10 100 1000
Diameter (nm)
dN/d
log(
Dp)
(par
t./cm
3)
11:56:23 16:14:38 16:34:41 16:41:03 Background average 12:50:59
Typical On Road Size Distributions - 40-55 mph Accelerations
1 October Accel. CA light load ISM Truck
1.00E+03
1.00E+04
1.00E+05
1.00E+06
1.00E+07
1 10 100 1000
Diameter (nm)
dN/d
log(
Dp)
(par
t./cm
3)
11:43:40 11:49:35 11:56:08 12:01:58 12:35:15 Background average
Ambient Temperature Appears to Have an Influence on Nanoparticle Formation. These Data Are for the Same Vehicle and Engine Conditions but Different Temperatures
1.0E+02
1.0E+03
1.0E+04
1.0E+05
1.0E+06
1 10 100 1000
Diameter (nm)
Nor
mal
ized
dN
/dlo
g(D
p) (p
art./
µ µµµm3 )
Accel 7 Oct, 21 C Accel 6 Oct, 11 C Cruise 7 Oct, 21 C Cruise 6 Oct, 11 C
The open symbols show runs made at 11 C
The closed symbols show runs made at 21 C
Average plume minus background SMPS size distributions normalized to 1 µm3/cm3
volume concentration are shown here
1.0E+06
1.0E+07
1.0E+08
1.0E+09
1.0E+10
1 10 100 1000
Dp [nm]
DN
/Dlo
gDp
[#/c
m3 ]
Tair=15CTair=25CTair=35CTair=42.5C
We Also See Clear Dilution Air Temperature Effects in U of M Single Stage Dilution Tunnel, DR=1000:1
Medium Duty Diesel EngineMeeting 1995 Heavy Duty Standards
Nanoparticles Are Formed by Modern Engines but They Are Semivolatile - Formed during Dilution, not in the Engine
1.00E+06
1.00E+07
1.00E+08
1.00E+09
1.00E+10
1 10 100 1000
Dp (nm)
dN/d
log(
Dp)
(par
t./cm
3 )
1800 rpm, 100% 1800 rpm, 100% + TD Light load cruise Light load cruise + TD
Federal Fuel (~330 ppm S)
+ TD denotes use of thermal denuder at 300 C
Light load cruise
Rated power
With thermal denuder
Formation of Semivolatile Nanoparticles
• It appears that sulfuric acid is the trigger for nanoparticle nucleation - at least at higher loads.
• However, there is not enough sulfuric acid in a typical diluting exhaust stream to explain observed nanoparticle diameter growth rates. (Khalek, Kittelson, and Brear, 2000).
• New measurements with a particle beam mass spectrometer show that 25 nm particles from engine exhaust are mainly hydrocarbons with some sulfuric acid. (P. Ziemann, UC Riverside; P. McMurry and D. Kittelson, U of Minn.).
Continuous Instruments Usually Track Well with Each Other During Chase Experiments
Typical CPC and Diffusion Charger ResponseCorrected for Differences in Instrument Time Response
0.00E+00
2.00E+04
4.00E+04
6.00E+04
8.00E+04
1.00E+05
1.20E+05
1.40E+05
1.60E+05
1.80E+05
2.00E+05
3:31:41PM
3:31:58PM
3:32:15PM
3:32:33PM
3:32:50PM
3:33:07PM
3:33:24PM
3:33:42PM
3:33:59PM
CPC
num
ber (
part
./cm
3)
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Diff
usio
n C
harg
er (c
m2/
m3)
CPC3025A Concentration (part./cm3) LQ1-DC Surface Area (cm2/m3)
7 October 1999
The Relationship Between Surface Area and Number Concentrations Gives a Mean Particle Size
Comparison of CPC and Diffusion Charger Response7 October 15:28-16:09
y = 2E-05x + 0.4968R2 = 0.7523
0.00E+00
2.00E+00
4.00E+00
6.00E+00
8.00E+00
1.00E+01
1.20E+01
1.40E+01
1.60E+01
0.00E+00 1.00E+05 2.00E+05 3.00E+05 4.00E+05 5.00E+05 6.00E+05 7.00E+05 8.00E+05
CPC Number, N, (part./cm3)
Diff
usio
n C
harg
er S
urfa
ce, S
, (cm
2/m
3)
The slope of this line is related to particle size. The diameter of average surface is given by:Das = (S/(πN)0.5
Instantaneous Concentration and Size during Trip on Suburban/Urban Freeway (ELPI)
0.00E+00
2.00E-02
4.00E-02
6.00E-02
8.00E-02
1.00E-01
1.20E-01
1.40E-01
1.60E-01
1.80E-01
12:57:36 13:12:00 13:26:24 13:40:48 13:55:12 14:09:36 14:24:00
Time
Dia
met
er ( µ µµµ
m)
0.00E+00
1.00E+04
2.00E+04
3.00E+04
4.00E+04
5.00E+04
6.00E+04
7.00E+04
8.00E+04
9.00E+04
Num
ber C
once
ntra
tion
(par
t./cm
3 )
Mean Diameter Particle Concentration
Lowry Tunnel
BehindTrucks
Instantaneous Concentration and Size during Trip on Suburban/Urban Freeway (ELPI)
0.00E+00
2.00E-02
4.00E-02
6.00E-02
8.00E-02
1.00E-01
1.20E-01
1.40E-01
1.60E-01
1.80E-01
2.00E-01
1.00E+02 1.00E+03 1.00E+04 1.00E+05
Number Concentration (part./cm3)
Dia
met
er, D
GN
( µ µµµm
)
Aged background particles
Freshly emitted particles
Instantaneous Concentration and Size during Trip on Suburban/Urban Freeway (ELPI)
0.00E+00
1.00E+04
2.00E+04
3.00E+04
4.00E+04
5.00E+04
6.00E+04
7.00E+04
8.00E+04
9.00E+04
13:43:41 13:45:07 13:46:34 13:48:00 13:49:26 13:50:53 13:52:19 13:53:46
Time
N (p
art./
cm3 )
4.00E-02
5.00E-02
6.00E-02
7.00E-02
8.00E-02
9.00E-02
1.00E-01
1.10E-01
1.20E-01
DG
N ( µ µµµ
m)
ELPI number ELPI DGN
Lowry Tunnel
Diameter
Number Concentration
Conclusions
• On-road chase experiments are a useful method for studying nanoparticle formation under real-world conditions
• Most of the nanoparticles observed behind vehicles form from particle precursors during dilution, not in the engine– Nanoparticle formation is sensitive to ambient temperature– Nanoparticles are removed by a thermal denuder– Heavy hydrocarbons and sulfuric acid appear to be the principal
precursors
• It will be very difficult to design a sampling and dilution method that simulates atmospheric dilution