Particle Number Size Distributions at an Urban Site in southern Sweden:

Estimates of the Contribution of Urban Particle Sources

Erik Swietlicki1, Andreas Massling1, Ingela Dahlberg1, Jakob Löndahl1, Adam Kristensson2, Henric Nilsson3, Susanna

Gustafsson3 and Matthias Ketzel4

1Division of Nuclear Physics, Lund University, Lund, Sweden2Department of Chemistry, Copenhagen University, Copenhagen, Denmark3Environment and Health Protection Board, City of Malmö, Malmö, Sweden

4Department of Atmospheric Environment, National Environmental Research Institute, Roskilde, Denmark

Research funded by the Swedish FORMAS

Paper 8A1, Session 8, IAC 2006

Motivation – Human Health

•CAFE estimates that fine particles (PM2.5) and ozone combined are responsible for 370,000 premature deaths each year in EU25, and the loss of 3.6 millions years of life annually.

(CAFE: Impact Assessment of the Thematic Strategy on Air Pollution and the Directive on “Ambient Air Quality and Cleaner Air for Europe”, SEC(2005)1133, Brussels, 21 Sept. 2005 (http://www.cafe-cba.org/)

•WHO estimates that exposure to fine particulate matter in outdoor air leads to about 100 000 deaths (and 725 000 years of life lost) annually in Europe. (WHO, World Health Report 2002, Geneva)

• For Sweden, Forsberg et al. (2005) estimated that the current population exposure to PM10 results in 5000 premature deaths annually.

RIP

(RIP = Respired Inhalable Particles … and died!)

Motivation – Climate

•Size-resolved emission data are often close to source (tunnels, tail-pipe, street canyons…).

•Regional/global scale models need the size distributions of the urban plume crossing over the city limits.

•Are aerosol dynamics (coagulation, condensation…) fast enough to significantly modify the urban plume aerosol size distribution?

0.01 0.1d p in µm

0x10 0

4x10 3

8x10 3

1x10 4

2x10 4

dN

/dlo

g(d

p)

AER O 3

1.E-04

1.E-03

1.E-02

1.E-01

1 10 100 1000Particle diameter (nm)

dN/d

logd

p (rel

ativ

e sc

ale)

Wood combustion

Traffic

Measurements sites – Southern Sweden

Vavihill

Malmö

Court House

Malmö

55 36' 23'' N, 13 0' 9'' E

Malmö SMPS system•Own design, manufacture and calibration

•Medium-long DMA (Vienna-type, own manufacture)

•Particle counter: TSI CPC 3760A

•10-551 nm

•Closed-loop (driers and filters in loop)

•Scanning mode (up and downscan, Labview software)

•CPC desmearing to improve time resolution

•Time resolution: 3 min

•RH and T sensors for data QA

•Measurements started April 2005

Court House, Malmö, Sweden(Urban Roof-top Measurement Site)

• Gas phase: NO, NO2, SO2, CO

• PM2.5, PM10

• Meteorological data, nearby mast

Environment and Health Protection Board,

City of Malmö, Sweden

The Vavihill siteRegional background – Southern Sweden

•Twin-DMPS (3-900 nm)

Aerosol Size DistributionsUrban Roof-top – Malmö, Sweden

April 2005 – April 2006

Mean Percentiles

Median

70%

90%

30%

10%

6 980 cm-3

StatisticsApril 2005 – April 2006

Particle concentration

Mean Median Max Min

Number (cm-3) 6 980 5820 89 200 559

Surface (µm2/cm3) 187 153 2 230 12.6

Volume (µm3/cm3) 7.27 5.44 102 0.12

Aerosol Size DistributionsUrban Roof-top – Malmö, Sweden

Mean PM2.5 10 µg/m3

National holidays have been omitted.

Aerosol Size DistributionsUrban Roof-top – Malmö, Sweden

April 2005 – April 2006Average Size Distributions

50 nm

Weekdays

Average size distributions for the various wind sectors.

Aerosol Size DistributionsUrban Roof-top – Malmö, Sweden

Harbour

Malmö

Harbour

Malmö city

Court House, Malmö(urban roof-top measurement site)

Sources to the urban aerosol (size distribution):

• Long-range transported regional background

• Urban sources (road traffic, ship traffic, industry,…)

• Heating: oil and wood combustion (minor sources in Malmö)

+ aerosol dynamics transforming the size distribution within the city limits (condensation, coagulation, deposition, dilution)

Attempt to separate:

•Urban contribution to the urban roof-top concentrations (Urban measurements – Regional Background)

• Local traffic contribution (Highest 20% [NO]/[NO2] ratios)

• Ship plumes (High [SO2], wind direction from harbour area)

Estimated Traffic ContributionMalmö Urban Roof-top

July 2005

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

10 100 1000Dp (nm)

dE

/dlo

gD

p (

x 10

14 k

m-1)

0

500

1000

1500

2000

2500

dn

/dlo

gD

p (

cm-3)

Average fleet, tunnel

Traffic model

Method suggested by Janhäll et al. (2004)

Local traffic contribution: Cases with highest 20% [NO]/[NO2] ratiosUrban background: Cases with lowest 20% [NOx] subtracted

Size-dependent emission factors derived from a Swedish tunnel study (Kristensson et al., 2004) are shown for comparison.

Tunnelstudy

EstimatedTraffic

Derived Traffic Contribution

Traffic distribution - Number

0

1000

2000

3000

4000

5000

6000

7000

8000

1 10 100 1000

Dp in nm

dN

/dlo

gD

p (

cm-3

)

Mode 12.9

Mode 25.3

Mode 67.7

Mode 1000

Mode 80

Mode 70

Sum

Mode GMDs: 13 nm, 25 nm, 68 nm

Rådhuset

Ship Traffic Contribution

Ship plumes from Malmö City

Harbour

0

20

40

60

80

100

120

140

160

00:00 02:00 04:00 06:00 08:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 00:00

SO

2 co

ncen

tratio

n (µ

g/m

3 )

SO2

ShipPlumes

Nucleation mode particlesfrom homogeneous nucleation

of H2SO4 + H20 ?

Urban Roof-top – Regional BackgroundVavihill – Malmö

Urban site(Malmö)

Backgrund(Vavihill)

Malmö City Contribution to the Urban Roof-top Aerosol

Mode GMDs: 8 nm, 38-39 nm, 95-100 nmFresh aerosol (traffic, ships,..) + processed within city limits

Weekdays Weekends

Malmö CityContribution

MalmöCity

Contr.

Malmö City Contribution to the Urban Roof-top Aerosol

Mode GMDs: 8 nm, 38-39 nm, 95-100 nmFresh aerosol (traffic, ships,..) + processed within city limits

Malmö CityContribution

Weekdays July 2005

Malmö CityContribution

Traffic

Ship?

Harbour Inlet

Tetramodal distribution

0

5000

10000

15000

20000

25000

30000

35000

10 100 1000

Dp

dN

/dlo

gD

p

Original distr.

Mode 1

Mode 2

Mode 3

Mode 4

Mode 1-4

Mode 1

N1(cm-3)

CMD1 (nm)

Sigma1

12500 8 1.64

Mode 2

N2(cm-3)

CMD2 (nm)

Sigma2

11100 47 1.45

Mode 3

N3(cm-3)

CMD3 (nm)

Sigma3

2300 115 1.6

Mode 4

N4(cm-3)

CMD4 (nm)

Sigma4

5100 24 1.6

The urban contribution seems to be from road traffic plus ship movements in the harbour.Could the size shift from 25 nm to 40 nm be caused by aerosol dynamics instead?

Method

Ketzel, M. and Berkowicz, R. (2005): Multi-plume aerosol dynamics and transport model for urban scale particle pollution. Atmospheric Environment 39, 3407-3420.

AERO3 Model (E. Vignati, JRC)

InputAssumptions:The background size distribution at Vavihill (3-modal)The estimated traffic emission size distribution (4-modal)Average wind speed = 4 m/sEmission density for Malmö = 230 (pt/cm3) m/s

Modelling Urban Aerosol Dynamics

Question: Can particles grow from 25 to 40 nm in the urban background?

0.01 0.1d p in µm

0.0x10 0

4.0x10 3

8.0x10 3

1.2x10 4

1.6x10 4

2.0x10 4

dN

/dlo

g(d

p)

AER O 3

t= 0 , 1 , 3 , 5 H O U R S

Regional background, Urban Traffic Emissions and Dilution,No Aerosol Removal process

Modelling Urban Aerosol Dynamics

0 h

1 h

3 h

5 h

Emissions

0.01 0.1d p in µm

0.0x10 0

4.0x10 3

8.0x10 3

1.2x10 4

1.6x10 4

2.0x10 4

dN

/dlo

g(d

p)

AER O 3

t= 0 , 1 , 3 , 5 H O U R S

0.01 0.1d p in µm

0.0x10 0

4.0x10 3

8.0x10 3

1.2x10 4

1.6x10 4

dN

/dlo

g(d

p)

AER O 3

Regional background, Urban Traffic Emissions and Dilution,No Aerosol Removal process

Regional background, Traffic Emissions, Dilution, Coagulation,Deposition with u*=1.33 m/s, No condensation

Modelling Urban Aerosol Dynamics

0 h

1 h

3 h

5 h

0.01 0.1d p in µm

0.0x10 0

4.0x10 3

8.0x10 3

1.2x10 4

1.6x10 4

2.0x10 4

dN

/dlo

g(d

p)

AER O 3

t= 0 , 1 , 3 , 5 H O U R S

0.01 0.1d p in µm

0.0x10 0

4.0x10 3

8.0x10 3

1.2x10 4

1.6x10 4

dN

/dlo

g(d

p)

AER O 3

0.01 0.1d p in µm

0x10 0

4x10 3

8x10 3

1x10 4

2x10 4

dN

/dlo

g(d

p)

AER O 3

Regional background, Urban Traffic Emissions and Dilution,No Aerosol Removal process

Regional background, Traffic Emissions, Dilution, CoagulationDeposition with u*=1.33 m/s, No condensation

Regional background, Traffic Emissions, Dilution, Coagulation, DepositionCondensation, Growth rate=6 nm/h, Condensing vapour conc. = 1.85 x 108 molec cm-3

Modelling Urban Aerosol Dynamics

0 h

1 h

3 h

5 h

Regional background, emissions, dilution, coagulation, deposition, condensation

0.01 0.1d p in µm

0x10 0

4x10 3

8x10 3

1x10 4

2x10 4

dN

/dlo

g(d

p)

AER O 3

0.01 0.1d p in µm

0.0x10 0

4.0x10 3

8.0x10 3

1.2x10 4

1.6x10 4

2.0x10 4

dN

/dlo

g(d

p)

AER O 3

t= 0 , 1 , 3 , 5 H O U R S

Modelling Urban Aerosol Dynamics

0 h 0 h

1 h1 h

Regional background, urban traffic emissions and dilution only

• Aerosol dynamics alone can not grow the 25 nm traffic mode to 40 nm. This latter mode is probably caused by ship traffic.

• Aerosol dynamics is nevertheless likely to affect the urban size distribution even within the city limits of a medium-sized city.

• The urban plume contribution to the rural bakground is not simply a linear combination of regional background plus urban emissions and dilution.

Particle Number Size Distributions at an Urban Site in southern Sweden: Estimates of the Contribution of Urban

Particle SourcesErik Swietlicki, Andreas Massling, Ingela Dahlberg, Jakob Löndahl, Adam

Kristensson, Henric Nilsson, Susanna Gustafsson and Matthias Ketzel

> Conclusions <

• The dominant sources to the urban roof-top aerosol size distribution were determined

and were identified as

• Long-range transport

• Local road traffic

• Ship traffic

• Aerosol dynamics play a role

Thank you for your attention!