FAST RESPONSE MEASUREMENTS FOR THE DISPERSION OF NANOPARTICLES

IN VEHICLE WAKE AND STREET CANYON

89TH AMS MEETING, PHOENIX, 11-15 JANUARY 09

PRASHANT KUMAR

ALAN ROBINS

REX BRITTER

POINTS FOR DISCUSSION

BACKGROUND

MEASUREMENTS

Application of a DMS500 for ambient measurements

Street canyon measurements

Vehicle wake measurements

Hypothesis

SUMMARY AND CONCLUSIONS

ACKNOWLEDGEMENTS

PRASHANT KUMAR 89TH AMS MEETING, PHOENIX, 11-15 JANUARY 09 2

BACKGROUND

Stringent emissions: particle mass emissions (↓), number (↑)

Current regulations address atmospheric particulate matter as PM10, PM2.5 mass concentration; not number concentration (PNC)

Ultrafine particles (< 100 nm); main component of ambient particles by number, produced mainly by vehicles, contribute most to PNC but little to PMC; these

are more toxic than coarse particles per unit mass

Progress hampered by lack of proven methods and instrumentation to measure PNCs

1 of 1

This work addresses:

application of a fast response DMS500, its suitability and best operating conditions for the measurements of PNDs in operational (vehicle wake) and controlled (street canyons) conditions

to determine the time scale over which competing influences of transformation and dilution processes affect dispersion of nanoparticles

to discuss the importance of particle dynamics (hypothesis) during ambient measurements and modelling of nanoparticles

PRASHANT KUMAR 89TH AMS MEETING, PHOENIX, 11-15 JANUARY 09 3

MEASUREMENTS

Measurement Campaigns: Street canyon (Pembroke Street) Vehicle wake (Chemical Engineering Department)

Instrument: Differential Mobility Spectrometer (DMS500) Response: 10 Hz, real time continuous Sampling flow rate: 8.0 lpm at 250 mb for 5-1000 nm

2.5 lpm at 160 mb for 5-2738 nm

Movies: 2stroke-idle, diesel drive by

1 of 10

PRASHANT KUMAR 89TH AMS MEETING, PHOENIX, 11-15 JANUARY 09 4

APPLICATION OF DMS500

Check the sensitivity level of the instrument

Identify the suitable operating conditions (mainly sampling frequency) of the instrument which maximised its utility

2 of 10

PRASHANT KUMAR 89TH AMS MEETING, PHOENIX, 11-15 JANUARY 09 5

MEASUREMENTS

0.E+00

2.E+04

4.E+04

6.E+04

8.E+04

1.E+05

1 10 100 1000D p (nm)

0.1 s Av Noise (10 Hz)1 s Av Noise (1 Hz)10 s Av Noise (0.1 Hz)0.1 s Av Roadside background (10 Hz)0.1 s Roadside (10 Hz)

0.E+00

2.E+04

4.E+04

6.E+04

8.E+04

1.E+05

1 10 100 1000

dN/d

logD

p (#

cm

–3)

0.8

0.6

0.4

0.2

0.0

1.0 105

Sensitivity of the DMS500. Both typical roadside and background PNDs were measured at the fastest (10 Hz) sampling frequency.

Smaller (1 Hz or lower) rather than maximal (10 Hz) sampling frequencies found appropriate, unless experiments relied critically upon fast response data

Suggested sampling frequencies used in later experiments (Kumar et al., 2008a–e):

measured PNDs well above instrument’s noise level

reduced size of data files to manageable proportions

STREET CANYON 3 of 10

Site 1: Pembroke Street

Kerb

Winds from NW

1.60 m Traffic flow (down-canyon) W = 11.75 m

66 m

Chemical Engineering Department

Measurement siteH 11.60 m

2.60 m

2.50 m

(Figures not to scale)3-cup vortex anemometer

Leeward side Windward side

Pembroke College Building

L 167 m

NWNE

SE

SWWind16.60 m

PRASHANT KUMAR 89TH AMS MEETING, PHOENIX, 11-15 JANUARY 09 6

MEASUREMENTS

Among several objectives (Kumar et al. 2008a-e, 2009), the goal of present work is to measure the lapse time (i.e. time between vehicular emissions and measurements at roadside).

STREET CANYON 4 of 10

PRASHANT KUMAR 89TH AMS MEETING, PHOENIX, 11-15 JANUARY 09 7

0

20

40

60

80

100

0 10 20 30 40 50

Sample (Nos.)

Lap

se ti

me

(s)

Cars and Vans

Other vehicles

Sample measurements showing lapse time at Pembroke Street. Winds were calm ( 1.5 m s–1) during measurements.

Sample measurements: ~ 50 cars and vans and ~ 50 other vehicles (buses, trucks, LDVs) . Average speed of vehicle 30±7 km h–1.

Average lapse time 45±6.

MEASUREMENTS

VEHICLE WAKE

How does PNDs evolve in the vehicle wake?

Are the transformation processes important during street-scale measurements?

5 of 10

PRASHANT KUMAR 89TH AMS MEETING, PHOENIX, 11-15 JANUARY 09 8

DMS500

DMS500

DMS500

Pembroke College

Chemical Engineering

Road NMS Buildings

Pembroke Street11.75 m

10 m

15 m5 mSampling point

NW

SE

SW NE

Vehicles

(Figures not to scale)

Site 2: Schematic diagram of sampling site showing sampling position.

MEASUREMENTS

At t=1.6 sec.

0

4000

8000

12000

1 10 100 1000

0

0.00005

0.0001

0.00015

VEHICLE WAKE 6 of 10

dN/d

logD

p (#

cm

-3)

At t=0.2 sec.

0

4000

8000

12000

10 100 1000

0

0.00005

0.0001

0.00015At t=0.3 sec.

0

4000

8000

12000

1 10 100 1000

0

0.00005

0.0001

0.00015At t=0.4 sec.

0

4000

8000

12000

1 10 100 1000

0

0.00005

0.0001

0.00015At t=0.5 sec.

0

4000

8000

12000

1 10 100 1000

0

0.00005

0.0001

0.00015

At t=0.6 sec.

0

4000

8000

12000

1 10 100 1000

0

0.00005

0.0001

0.00015At t=0.9 sec.

0

4000

8000

12000

1 10 100 1000

0

0.00005

0.0001

0.00015At t=0.7 sec.

0

4000

8000

12000

1 10 100 1000

0

0.00005

0.0001

0.00015At t=0.8sec.

0

4000

8000

12000

1 10 100 1000

0

0.00005

0.0001

0.00015

dM/d

logD

p (μ

gm c

m-3) At t=0.1 sec.

0

4000

8000

12000

1 10 100 1000Dp (nm)

dN/d

ogD

p(#

cm-3

)

0

0.00005

0.0001

0.00015

dM/d

ogD

p(?

gm c

m-3

)

NumberMass

At t=0.1 sec.

0

4000

8000

12000

1 10 100 1000Dp (nm)

-

0

0.00005

0.0001

0.00015

dM/d

ogD

p(?

gm c

m-3

)

NumberMass

At t=0.1 sec.

0

4000

8000

12000

1 10 100 1000Dp (nm)

dN/d

ogD

p(#

cm-3

)

0

0.00005

0.0001

0.00015

dM/d

ogD

p(?

gm c

m-3

)

NumberMass

At t=0.1 sec.

0

4000

8000

12000

1 10 100 1000Dp (nm)

-

0

0.00005

0.0001

0.00015

dM/d

ogD

p(?

gm c

m-3

)

NumberMass

At t=0.2 sec.

0

4000

8000

12000

1 10 100 1000

0

0.00005

0.0001

0.00015

0

4000

8000

12000

1 10 100 1000

0

0.00005

0.0001

0.00015At t=0.4 sec.

0

4000

8000

12000

1 10 100 1000

0

0.00005

0.0001

0.00015At t=0.6 sec.

0

4000

8000

12000

1 10 100 1000

0

0.00005

0.0001

0.00015At t = 0.5 sec.

0

4000

8000

12000

1 10 100 1000

0

0.00005

0.0001

0.00015

Site background

Site background

t=–0.7s t=–0.6s t=–0.5s t=–0.4s t=–0.3s

t=– 0.2s t=–0.1s t=0.0s t=0.1s t=0.2s

t=0.3s t=0.4s t=0.5s t=0.6s t=0.7s

First evidence of exhaust emissions

Clear bi-modal distribution Peak (number and mass)

Evolution starts

1 10 100 1000 1 10 100 1000 1 10 100 1000 1 10 100 1000 1 10 100 1000

Dp (nm)

PRASHANT KUMAR 89TH AMS MEETING, PHOENIX, 11-15 JANUARY 09 9

MEASUREMENTS

At t=2.6 sec.

0

4000

8000

12000

1 10 100 1000

0

0.00005

0.0001

0.00015

At t=2.1 sec.

0

4000

8000

12000

1 10 100 1000

0

0.00005

0.0001

0.00015

At t=2.5 sec.

0

4000

8000

12000

1 10 100 1000

0

0.00005

0.0001

0.00015At t=2.4 sec.

0

4000

8000

12000

1 10 100 1000

0

0.00005

0.0001

0.00015

At t=2.3 sec.

0

4000

8000

12000

1 10 100 1000

0

0.00005

0.0001

0.00015

At t=2.2 sec.

0

4000

8000

12000

1 10 100 1000

0

0.00005

0.0001

0.00015

At t=2.0 sec.

0

4000

8000

12000

1 10 100 1000

0

0.00005

0.0001

0.00015

At t=1.9 sec.

0

4000

8000

12000

1 10 100 1000

0

0.00005

0.0001

0.00015

At=1.8 sec.

0

4000

8000

12000

1 10 100 1000

0

0.00005

0.0001

0.00015

At t=1.7 sec.

0

4000

8000

12000

1 10 100 1000

0

0.00005

0.0001

0.00015NumberMass

Vehicle Wake 7 of 10

dN/d

logD

p (#

cm

-3)

dM/d

logD

p (μ

gm c

m-3)

1 10 100 1000 1 10 100 1000 1 10 100 1000 1 10 100 1000 1 10 100 1000

Dp (nm)

Similar to site background

Rapid Evolution

t=0.8s t=0.9s t=1.0s t=1.1s t=1.2s

t=1.3s t=1.4s t=1.5s t=1.6s t=1.7s

Similar to site background

–0.7 s to 0.0 s (background PNC) – time to reach to DMS500

Evolution to reach to background takes 1.0 s

PRASHANT KUMAR 89TH AMS MEETING, PHOENIX, 11-15 JANUARY 09 10

MEASUREMENTS

-0.8 -0.5 -0.2 0.1 0.4 0.7 1.0 1.3 1.6 21.70.00E+00

3.00E-06

6.00E-06

9.00E-06

1.20E-05

1.50E-05

Time (s)

PMC (without background)PMC (total)

-0.8

-0.6

-0.4

-0.2 0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.60.00E+00

3.00E-06

6.00E-06

9.00E-06

1.20E-05

1.50E-05

PM

C (

μgm

cm

–3)

10– 5

0.0

0.3

0.6

0.9

1.2

1.5

1 10 100 1000 10000

Post–evolutionPre–evolution Evolution

-0.8 -0.5 -0.2 0.1 0.4 0.7 1.0 1.3 1.6 21.70.00E+00

4.00E+04

8.00E+04

1.20E+05

1.60E+05

2.00E+05

Time (s)

PNC (without background)

PNC (total)

105

-0.8

-0.6

-0.4

-0.2 0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.60.00E+00

4.00E+04

8.00E+04

1.20E+05

1.60E+05

2.00E+05

PN

C (

# cm

–3)

0.0

0.4

0.8

1.2

1.6

2.0

1 10 100 1000 10000

Post–evolutionPre–evolution Evolution

VEHICLE WAKE 8 of 10

Time to evolve PNDs in vehicle wake is far lesser ( 1 s)

than time to measure PNDs at roadside (45 ± 6 s)

Dilution is quick enough, and

effect of transformation processes is generally over by the time measurements made at road side.

See Kumar et al. (2008d) for details

PRASHANT KUMAR 89TH AMS MEETING, PHOENIX, 11-15 JANUARY 09 11

MEASUREMENTS

14

15

16

17

18

19

20

-0.8 -0.5 -0.2 0.1 0.4 0.7 1.0 1.3 1.6

Time (s)

Pea

k di

stri

butio

n di

amet

er (

nm)

0

15

30

45

60

75

90

Pea

k di

stri

butio

n di

amet

er (

nm)

PDD (nucleation mode)PDD (accumulation mode)

VEHICLE WAKE 9 of 10

PRASHANT KUMAR 89TH AMS MEETING, PHOENIX, 11-15 JANUARY 09 12

MEASUREMENTS

Pre-evolution Evolution Post-evolution

Distributions Identical Rapid change Identical

Nucleation 15.4 nm 15.4 -18 nm* 15.4 nm

Accumulation ~87 nm† ~87 nm † ~87 nm †

Mass Negligible below 30 nm; small amount of mass between 30 and 300 nm

Time ~0.7 s ~ 1.0 s ~ 10 s (street ventilation)

Temporal change in peak diameters of 0.1 s averaged

PNDs for both nucleation and accumulation modes.

*Shift in peak mode diameters shows influence of transformation processes since dilution should change the PNDs proportionally and should not change the peak mode diameters.

†Nearly unchanged peak mode diameters in accumulation mode (30-300 nm) suggested that dilution is the most dominant process to reduce the PNDs.

HYPOTHESIS 10 of 10

See Kumar et al. (2008b, c and d) for detailed testing of hypothesis

PRASHANT KUMAR 89TH AMS MEETING, PHOENIX, 11-15 JANUARY 09 13

“The effect of transformation processes on the particles is nearly over by

the time these particles are measured at roadside and total particle

numbers are then assumed to be conserved”.

MEASUREMENTS

SUMMARY AND CONCLUSIONS

An advanced particle spectrometer was successfully applied to measure PNDs and PNCs in street canyons and in vehicle wake where fast response nature of an instrument is essential.

Vehicle wake measurements showed that the PNDs evolved rapidly in the wake of a moving diesel car and became similar to background PNDs within 1 s.

This evolution was significantly smaller than the typical time ( 456 s) for traffic emissions to reach the roadside in a street canyon.

Comparison of these time scales suggested a hypothesis that the effect of transformation processes is generally complete by the time particles are measured at roadside and total particle numbers can then be assumed to be conserved.

The hypothesis allows to ignore the particle dynamics during street canyon measurements and found to be useful for the modelling of the dispersion of nanoparticles in street canyons (Kumar et al. 2008, 2009).

1 of 1

PRASHANT KUMAR 89TH AMS MEETING, PHOENIX, 11-15 JANUARY 09 14

RELATED ARTICLES FOR DETIALED INFORMATION 1 of 1

JOURNAL• Kumar, P., Garmory, A., Ketzel, M., Berkowicz, R., 2009. Comparative study of measured and modelled number concentration of nanoparticles in an urban street canyon. Atmospheric Environment 43, 949-958.• Kumar, P., Fennell, P., Symonds, J., Britter, R., 2008e. Treatment for the losses of ultrafine aerosol particles in long sampling

tubes during ambient measurements. Atmospheric Environment 42, 8831-8838.• Kumar, P., Fennell, P., Hayhurst, A., Britter, R., 2008d. Street versus rooftop level concentrations of fine particles in a Cambridge Street Canyon. Boundary–Layer Meteorology (in press, doi:10.1007/s10546-008-9300-3). • Kumar, P., Fennell, P., Britter, R., 2008c. Effect of wind direction and speed of the dispersion of nucleation and accumulation

mode particles in an urban street canyon. Science of the Total Environment 402, 82-94.• Kumar, P., Fennell, P., Britter, R., 2008b. Pseudo-simultaneous measurements for the vertical variation of coarse, fine and

ultrafine particles in an urban street canyon. Atmospheric Environment 42, 4304-4319.• Kumar, P., Fennell, P., Britter, R., 2008a. Measurements of the Particles in the 5-1000 nm range close to the road level in an

urban street canyon. Science of the Total Environment 390, 437-447.

CONFERENCE• Kumar, P., Ketzel, M., Robins, A., Britter, R., 2009. Street-scale modelling of nanoparticles using a simplified approach and an

operational model. 7th International Conference on Air Quality-Science and Application, Istanbul (Turkey), 24-27 March 2009.• Kumar, P., Fennell, P., Britter, R., 2008h. The influence of Ambient Meteorology on Nanoparticle Concentration in an Urban

Setting. Cambridge Particle meeting, Cambridge (UK), 16 May 2008.• Kumar, P., Britter, R., 2008g. Measurements and dispersion modelling on traffic-emitted particles in the urban environment .

National Environment Research Institute (Denmark), 7 May 2008. • Kumar, P., Fennell, P., Britter, R., 2007d. Measurement and dispersion behaviour of particles in various size (5 nm>Dp<1000

nm) ranges in a Cambridge Street Canyon. Proceedings of the 11th International Conference on Harmonisation within Atmospheric Dispersion Modelling for Regulatory Purposes, Cambridge (UK), 2-5 July 2007, pp. 368-372.

• Kumar, P., Fennell, P., Britter, R., 2007c. The measurement of fine particles for the study of their dispersion and of street-scale air quality. UK Atmospheric Aerosol Network (UKAAN) Workshop, University of Reading, Berkshire (UK), 6-7 June 2007.

• Kumar, P., Britter, R., 2007b. Particulate Matter: Importance, Regulations and Historical Perspective. ‘Nirmaan’, IIT Delhi Civil Engineering Society, Issue 2, May 2007 pp. 38-42.

• Kumar, P., Britter, R., Langley, D., 2007a. Street versus rooftop level concentrations of fine particles in a Cambridge Street Canyon. 6th International Conference on Urban Air Quality Limassol (Cyprus), 27-29 March 2007, pp. 135-138.

PRASHANT KUMAR 89TH AMS MEETING, PHOENIX, 11-15 JANUARY 09 15

ACKNOWLEDGEMENTS

University of Surrey

Cambridge University Department of Engineering

Cambridge Philosophical Society

Cambridge Commonwealth Trust

Pembroke College, Cambridge

Dr. Paul Fennell (Imperial College, London) – help during experiments

PRASHANT KUMAR 89TH AMS MEETING, PHOENIX, 11-15 JANUARY 09 16

TRAVEL GRANT

1 of 1

THANK YOU

CONTACT

PRASHANT KUMAR

Email: pp286@cam.ac.uk

Webpage: http://people.pwf.cam.ac.uk/pp286

Vehicle Wake EXTRA SLIDE

PRASHANT KUMAR 89TH AMS MEETING, PHOENIX, 11-15 JANUARY 09 18

MEASUREMENTS

pp

p Dd

dNDM

Dd

dM

log)(

log

fDppp DCDM ')(

Estimation of PMDs

For dM/dlogDp in gm cm–3, M(Dp) is in Kg and Dp is in nm,

(C’ = 6.95 10–24) is a constant

p (= 1) is the assumed density of a particle in g cm–3

Df (= 3) is the fractal dimension for a spherical particle (Park et al. 2003).