Ian Longley

Street canyon aerosol pollutant transport Street canyon aerosol pollutant transport measurements in Manchestermeasurements in Manchester

I.D. Longley, M.W. Gallagher,J.R. Dorsey, M. Flynn, K. Bower, I. Barlow

J.R. Allan, M.R. Alfarra, H. Coe

Ian Longley

Aerosol in Urban Street Canyons

• Fine aerosol, linked to adverse health effects (COMEAP, 2001, EPAQS,2000, Colville et al, 2001).

• Fine aerosol from vehicle emissions.

• Street canyons act as major emission sites.

• Large numbers of people exposed.• Canyons re-circulate and trap

pollutants.• Canyon emissions transported

across and beyond city – affecting chemical and radiative atmospheric properties and the biosphere.

• Need to understand transport within, and emission from, urban street canyons.

Ian Longley

SCAR – Street Canyon Aerosol Research

• Regulatory dispersion models are based upon a simple transport mechanism – PM10 only.

• Numerical modelling – simple canyons.• Field studies are rare.• SCAR to apply eddy correlation techniques.• Aim: Parameterised size-

segregated aerosol emission rates.

Ian Longley

Experimental site – Princess Street, Manchester

270

180

90

0

Town Hall

N

19 13 9 10 11 15 8

1 9 Estimated building heights

22-28

SCAR van

SCAR platform lift

Ian Longley

SCAR measurements

•SMPS (TSI 3080 + nano DMA)

•OPC (PMS ASASP-X)

•FSSP

•20 Hz sonic anemometers

•18m mast

•Platform lift for profiling

•Mobile turbulence system

•4 campaigns in 2001: (3 x 1 week, 1 x 2 weeks)

Ian Longley

Mean ultrafine aerosol spectra

• Left: SMPS spectrum from UMIST Land Rover Discovery TDi

• Left: average SMPS spectrum from SCAR, 2m height

mean road-side SMPS spectrum at 2m

1.E+03

1.E+04

1.E+05

10 100 1000

Dp / nm

dN/d

logD

p

Aerosol spectrum 2m behind Land Rover exhaust

1.E+04

1.E+05

1.E+06

1.E+07

1.E+08

10 100 1000

Dp / nm

dN

/dlo

gD

p ,

cm-3

3000 rpm1000 rpm

Ian Longley

Aerosol Chemistry(from Aerosol Mass Spectrometer, J.R. Allen, M.R. Alfarra, H.Coe)

2.0

1.5

1.0

0.5

0.0

2 3 4 5 6 7 8 9

1002 3 4 5 6 7 8 9

1000Aerodynamic Diameter (nm)

2.0

1.5

1.0

0.5

0.0

dM/d

logD

p (µ

gm-3

)

Nitrate Sulphate Organics

Period 1(Low Winds)

Period 2(High Winds)

•Mode in the mass spectra at around 100-200nm consisting of aliphatic organic chemicals.

•Organic activity within the Manchester sampling periods correlates well with NOx activity.

Ian Longley

Temporal variation in fine aerosol spectra (4.6nm<Dp<160nm)

• Total number concentrations generally follow traffic flow

• Road-side day-time concentrations are generally greater than night-time by a factor of around 4.

• Day-time and night-time spectra are the same shape.

SMPS mean spectra, day and night, at 4m,SW perp. winds only

100

1000

10000

100000

1000000

1 10 100 1000

Dp / nm

dN/d

logD

p

day

night

SCAR-4 SMPS diurnal average total number concentration,4.7nm<Dp<157nm, profiles periods only

0

20000

40000

60000

80000

100000

120000

140000

00:00 06:00 12:00 18:00 00:00

local time

dN

/ cm

-3 4m9m14m17m

Ian Longley

Mean air flow: Channelling

SCAR relationship between wind directionabove and within canyon

0

90

180

270

360

0 90 180 270 360

roof wind direction (relative to sonic)

so

nic

win

d d

ire

ctio

n(r

ela

tiv

e to

can

yon

)

southnorth

Ian Longley

Mean air flow: Vertical flowSCAR mean wind angles

separated by location of anemometer within canyon

-90

-60

-30

0

30

60

90

0 90 180 270 360

roof wind direction (relative to sonic)

so

nic

vert

ical w

ind

an

gle

southnorth

Ian Longley

Mean air flow: Vertical flowSCAR mean wind angles

separated by location of anemometer within canyon

-90

-60

-30

0

30

60

90

0 90 180 270 360

roof wind direction (relative to sonic)

so

nic

vert

ical w

ind

an

gle

southnorth

Ian Longley

Mean air flow: Up-canyonSCAR mean wind angles

separated by location of anemometer within canyon

-90

-60

-30

0

30

60

90

0 90 180 270 360

roof wind direction (relative to sonic)

so

nic

vert

ical w

ind

an

gle

southnorth

Ian Longley

Mean air flow: NE perpendicularSCAR mean wind angles

separated by location of anemometer within canyon

-90

-60

-30

0

30

60

90

0 90 180 270 360

roof wind direction (relative to sonic)

so

nic

vert

ical w

ind

an

gle

southnorth

Ian Longley

Mean air flow: SW perpendicularSCAR mean wind angles

separated by location of anemometer within canyon

-90

-60

-30

0

30

60

90

0 90 180 270 360

roof wind direction (relative to sonic)

so

nic

vert

ical w

ind

an

gle

southnorth

Ian Longley

Influence of wind speed and direction on fine aerosol number concentrations – 1. PARALLEL FLOW

SMPS total number concentration seperated by wind sector,against roof-top wind speed, day-time at 4m

0

20000

40000

60000

80000

100000

0 2 4 6 8 10

Uroof / ms-1

Nto

tal /

cm

-2s

-1

up-canyonNEperpSW perp

SMPS mean spectra seperated by wind sector,against roof-top wind speed, day-time at 4m

100

1000

10000

100000

1000000

1 10 100 1000

Dp / nm

dN

/dlo

gD

p

up-canyonNE perpSW perp

Ian Longley

Influence of wind speed and direction on fine aerosol number concentrations – 2. NE PERPENDICULAR

SMPS total number concentration seperated by wind sector,against roof-top wind speed, day-time at 4m

0

20000

40000

60000

80000

100000

0 2 4 6 8 10

Uroof / ms-1

Nto

tal /

cm

-2s

-1

up-canyonNEperpSW perp

• Canyon vortex blows emissions away from instruments

SMPS mean spectra seperated by wind sector,against roof-top wind speed, day-time at 4m

100

1000

10000

100000

1000000

1 10 100 1000

Dp / nm

dN

/dlo

gD

p

up-canyonNE perpSW perp

Ian Longley

Influence of wind speed and direction on fine aerosol number concentrations – 3. SW PERPENDICULAR

SMPS total number concentration seperated by wind sector,against roof-top wind speed, day-time at 4m

0

20000

40000

60000

80000

100000

0 2 4 6 8 10

Uroof / ms-1

Nto

tal /

cm

-2s

-1

up-canyonNEperpSW perp

• Canyon vortex blows emissions towards instruments

• Flow at pavement level disconnected from roof-top wind

SMPS mean spectra seperated by wind sector,against roof-top wind speed, day-time at 4m

100

1000

10000

100000

1000000

1 10 100 1000

Dp / nm

dN

/dlo

gD

p

up-canyonNE perpSW perp

Ian Longley

Vertical concentration gradients

SMPS mean spectra at two heights,day-time, UP-CANYON winds only

100

1000

10000

100000

1000000

1 10 100 1000

Dp / nm

dN

/dlo

gD p

4m17m

Ian Longley

Vertical concentration gradients

SMPS mean spectra at two heights,day-time, SW perp. winds only

100

1000

10000

100000

1000000

1 10 100 1000

Dp / nm

dN

/dlo

gD p

4m17m

Ian Longley

Accumulation mode (100nm<Dp<1m) aerosol emission fluxes

SCAR SASUA: Above Edinburgh*SASUA Edinburgh Average Diurnal Particle Flux

Time (Local)

00:00 04:00 08:00 12:00 16:00 20:00 00:00

Par

ticle

Flu

x (#

cm

-2 s

-1)

0

10000

20000

30000

40000

50000

SASUA Edinburgh Average Diurnal Sensible Heat Flux

Time (Local)

00:00 04:00 08:00 12:00 16:00 20:00

Sen

sibl

e H

eat F

lux

(W m

-2)

-20

0

20

40

60

80

100

120

*Dorsey, J.R. et al Atmos. Environ. Vol.36, pp. 791-800.

Diurnal average of total number flux at two heights, 23rd-25th Oct

-500

0

500

1000

1500

2000

2500

00:00 06:00 12:00 18:00 00:00

local time

tota

l nu

mb

er f

lux

/ cm

-2s-1

5m18m

Diurnal average of traffic flow and heat flux, 23rd-25th Oct

-1000

0

1000

2000

3000

4000

5000

00:00 06:00 12:00 18:00 00:00

local time

tota

l nu

mb

er f

lux

/ cm

-2s-1

-10

0

10

20

30

40

50

trafficheat flux

Ian Longley

Horizontal fluxes

Diurnal average of total number LONGITUDINAL flux at two heights, 23rd-25th Oct

0

20000

40000

60000

80000

100000

120000

00:00 06:00 12:00 18:00 00:00

local time

flu

x / c

m-2

s-1

0

1000

2000

3000

4000

5000

6000

traf

fic

/ hr

-1

5m18mtraffic

Ian Longley

Coarse particle fluxes

Wind speed [m s-1]

0 2 4 6 8 10 12 14 16

Flu

x (1

.9 t

o 3.

2 m

) [#

cm

-2 s

-1]

0

2

4

6

8

F = 0.0024 u2.92

SASUA All Experiments Aerosol Eddy Flux Measurements

dp>1.9 m Mode- CEH instrumentWind driven re-suspension

Diurnal average of coarse particle number flux (0.4<Dp<3m), 23rd-25th Oct

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

00:00 06:00 12:00 18:00 00:00

local time

flu

x / c

m-2

s-1

0

1

2

3

4

5

6

7

8

9

10

roo

f to

p w

ind

sp

eed

Uro

of /

ms

-1

5m fluxUroof

Ian Longley

Vertical turbulence

SCAR-4 fixed sonic (at 3.5m) w/U against wind speed, Ufor day-time and night-time periods

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 0.5 1 1.5 2 2.5 3 3.5

U / ms-1

w/U

7 - 17 GMT1 - 6 GMTmodel - daymodel - night

Ian Longley

Parameterisation for w

Traffic-induced turbulence

Traffic-induced vertical turbulence wt calculated from mast data,and local traffic flow

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

00:00 06:00 12:00 18:00 00:00

hour of day / GMT

calc

ula

ted

w

t

sig wtPrincess StManc Way

Ian Longley

SCAR-4 modelled and measured (fixed mast at 3.5m) w/U

0.1

1

10

0.1 1 10

U / ms-1

w/U

day modelday datanight modelnight data

Parameterisation for w

= 0.16 at a height of 3.5mwt = 0.0135 T1/2

T = traffic flow rate (hr-1)

2/122wtw U

Ian Longley

Turbulent variances: w/U profiles

SCAR-4 platform sonic vertical profile of mean normalised

variances (U > 1.5 ms-1)

0

2

4

6

8

10

12

14

16

18

20

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

u,v,w/U

z / m

sig w/U

Ian Longley

Turbulent variances: u/U profiles

SCAR-4 platform sonic vertical profile of mean normalised

variances (U > 1.5 ms-1)

0

2

4

6

8

10

12

14

16

18

20

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

u,v,w/U

z / m

sig u/U

Ian Longley

Turbulent variances: v/U profiles

SCAR-4 platform sonic vertical profile of mean normalised

variances (U > 1.5 ms-1)

0

2

4

6

8

10

12

14

16

18

20

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

u,v,w/U

z / m

sig v/U

Ian Longley

Spatial variation in w/U:1. Sheltered zone

Above: U/Uroof Below: w/U

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 0.5 1 1.5 2 2.5 3 3.5

U / ms-1

w/U

7 - 17 GMT1 - 6 GMTmodel - daymodel - night

Plan views of canyon

Ian Longley

Spatial variation in w/U:2. Convergence

Above: U Below: w/U

Ian Longley

Conclusions

The flux of accumulation mode aerosol (100nm<Dp<3m) have been measured in a city centre street canyon and found to be related to urban heat emission and traffic activity.

Street-level fine aerosol has been shown to be influenced by asymmetrical vortex flow within the canyon.

A vertical gradient was found in fine aerosol number concentrations below roof level.

A weak positive vertical gradient was seen in turbulent variances. However, greatly enhanced variances were seen at the bottom of the canyon.

A parameterisation has been derived for w based upon local wind speed and traffic flow rate.

Ian Longley

Forthcoming analysis

• More street-level accumulation mode flux data• Profiles of coarse aerosol concentrations• Improved parameterisation for wind-driven re-

suspension• Spectral & quadrant analysis• SCAR-5: suburban street canyon• Improved parameterisation for turbulence,

including traffic-layer turbulence