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