I.D. Longley, J.R. Dorsey, M.W. Gallagher, J.D. Allan, M.R. Alfarra, H.Coe

Physics Department, UMIST, Manchester, U.K.

Exposure to ultrafine particles from traffic in city streets and the urban atmosphere

PM10

Particles monitored as PM10 (< 10 m) across Europe

PM10 is epidemiologically linked to mortality and morbidity

Urban particle sources and sizes

Dp / m

0.001 0.01 0.1 1 10 100

dV/d

log(Dp)

/ m

3 m

-3

0.01

0.1

1

10

100Vehicle emissions,

combustion

Long-range transport, secondary particles

Dust, wear products,

biological particles, minerals

Measured in Princess Street, Manchester (Atmos. Environ. 37, 1563-71)

PM10

Ultrafine Particles – mass and number

Dp / m

0.001 0.01 0.1 1 10 100

dV/d

log(Dp)

/ m

3 m

-3

0.01

0.1

1

10

100

Dp / m

0.001 0.01 0.1 1 10 100

dN/d

log(Dp)

/ cm

-3

1e-1

1e+0

1e+1

1e+2

1e+3

1e+4

1e+5

1e+6

Above: mass size distribution from Manchester street canyon

Above: number size distribution from Manchester street canyon

Typical UK urban concentrations:

PM10: ~ 20 g m-3

Most particles are ultrafine, but have tiny contribution to PM10PM0.1: ~ 1 g m-3

Ultrafine Particles in the body•Ultrafines (UFP) efficiently deposit to alveolar walls

•Overload can cause chronic inflammation and irreversible damage to tissues and defences

•Inflammatory response triggers systemic reaction in cardiovascular system – increases in blood viscosity, formation and disruption of plaques, heart rate variability.

•Can lead to arrythmia, ischaemia and heart attack (immediately or in future)

Effects seen in ‘non-toxic’ particles –

is toxicity in size, surface area or composition???

Spatial variation in urban PM10 (1)

2005 predicted annual mean PM10 / g m-3

NOTE scale divisions

Variation from 9.25 – 10.50 g m-3 across most of city

Prediction dominated by ~ 8 g m-3 regional background

Spatial variation in urban PM10 (2)

Dominated by city-wide episodes linked to meteorology.

0

10

20

30

40

50

60

70

80

90

100

22-Jan 23-Jan 24-Jan 25-Jan 26-Jan 27-Jan 28-Jan

PM

10 /

gm

-3

0

5

10

15

20

25

win

d s

pee

d /

kno

ts

PiccadillyEcclesU

Temporal variation in PM10

PM10 is dominated by extra-urban sources and processes.

Implies that little can be achieved by local intervention

Urban Ultrafine Particles

Toxicity lies in ultrafine fraction

Traffic is the dominant urban source

Not routinely monitored

Much stronger spatial gradients and temporal variability

Manchester from UMIST Building

dM

/dlo

gD

a (g

m-

3)

Aerodynamic Diameter (nm)

1.0

0.8

0.6

0.4

0.2

0.0

dM

/dlo

gD a

(µg

m-3

)

2 3 4 5 6 7 8 9100

2 3 4 5 6 7 8 91000

2 3

Aerodynamic Diameter (nm)

OrganicsSulphateNitrateAmmonium

Manchester winter

4

3

2

1

0

dM

/dlo

gD

a (µ

g m

-3)

2 3 4 5 6 7 8 9100

2 3 4 5 6 7 8 91000

2 3

Aerodynamic Diameter (nm)

SulphateNitrateOrganicsAmmonium

Manchester_Summer

3.0

2.5

2.0

1.5

1.0

0.5

0.0<20

0nm

Par

ticul

ate

Org

anic

s (µ

gm-3

)

14012010080604020NOx (ppb)

Urban particle speciated mass size distributions

UFP mostly organic compounds

Also:

•Black carbon

•Sulphuric acid

Urban background UFP

•Few studies: Edinburgh, Leipzig, Helsinki, Brisbane

•9 – 80% higher in winter than summer (low temperature favours gas-particle conversion)

•Lower concentrations on weekends, indicating reduced emission

Edinburgh measurement site (SASUA, 1999-2001)

SASUA diurnal particle number flux (Oct/Nov)

0

5000

10000

15000

20000

25000

0:00 6:00 12:00 18:00 0:00Time

N (

cm-3

)

0

10000

20000

30000

40000

50000

60000

70000

80000

90000

100000

FN (

cm-2

s-1

)

ConcentrationFlux

-50

0

50

100

150

200

0:00 6:00 12:00 18:00 0:00

Time

H (W

m-2

)

Oct/Nov

`

Below: sensible surface heat flux

•Diurnal cycle in urban ventilation related to heat flux cycle

•Morning concentration peak related to reduced ventilation

SASUA diurnal particle number flux (May)

Below: sensible surface heat flux

•Higher heat flux, but slightly lower urban ventilation flux, due to lower emission rates

•Earlier sunrise and stronger heating means morning concentration peak is diminished.

•This effect dependent upon latitude.

0

5000

10000

15000

20000

25000

0:00 6:00 12:00 18:00 0:00Time

N (

cm-3

)

0

10000

20000

30000

40000

50000

60000

70000

80000

90000

100000

FN (

cm-2

s-1

)

ConcentrationFlux

-50

0

50

100

150

200

0:00 6:00 12:00 18:00 0:00

Time

H (

W m

-2)

Oct/NovMay

`

Manchester Piccadilly (2000)

Pic of AUN hut

PiccadillyGardens

Busy roads

Busy roads(buses only)

Instruments

Mean Piccadilly UFP concentrations

0

5000

10000

15000

20000

25000

30000

Sat Sun Mon Tue Wed Thu Fri

N /

cm-3

all dataexcl. holidays

0

10000

20000

30000

40000

50000

60000

15-Mar 4-May 23-Jun 12-Aug 1-Oct

N /

cm-3

Above: means by day of week

Below: daily means (Tue – Fri)

Excursions and underlying means

0

50000

100000

150000

200000

250000

300000

350000

400000

0:00 12:00 0:00

N /

cm

-3

Above: Example day

0

10000

20000

30000

40000

50000

60000

0:00 6:00 12:00 18:00 0:00time / GMT

N /

cm-3

all dataunderlying

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

April May June July August

all data

unerlying‘excursions’ contribute an

average 7 300 cm-3 in daytime, a 28 % increase over underlying

mean

Concentration rose of excursions

PiccadillyGardens

0

60

120

180

240

300

360

0:00 6:00 12:00 18:00 0:00

dd

dd

N

0:00 6:00 12:00 18:00 0:00

0

50000

100000

150000

200000

250000

300000

N /

cm

-3

dd

N

18th April12th April

Above: excursions only

Excursions clearly related to periods when monitor is downwind of major traffic sources

SW perp

Up-canyon

NE perp

Down-canyon

Measurement site

SCAR – Princess Street, Manchester (2001)

One-way traffic

Up to 1100 vehicles h-1

Including buses

SCAR-4 Mean street-level aerosol number size distribution

Dp / m

0.001 0.01 0.1 1 10 100

dN/d

log(Dp)

/ cm

-3

1e-1

1e+0

1e+1

1e+2

1e+3

1e+4

1e+5

1e+6

Dp / m

0.001 0.01 0.1 1 10 100

dN/d

log(Dp)

/ cm

-3

1e-1

1e+0

1e+1

1e+2

1e+3

1e+4

1e+5

1e+6

SCAR-4 Mean street-level aerosol number size distribution

N0.1 Ultrafine particle concentration

Estimating background N0.1 from NOx

y = 145.21x + 1629.3R2 = 0.6247

0

5000

10000

15000

20000

25000

0 20 40 60 80 100

street-level NOx / ppb

stre

et-l

evel

N0.

1 /

cm-3

SCAR site

Network monitor

Predicts background range of 4 000 – 9 000 cm-3

Ultrafines number size distribution in channelled flow

Dp / nm

1 10 100 1000dN

/dlo

g(Dp)

/ cm

-3103

104

105

106

channelled

Ultrafines number size distribution in recirculating flow

Dp / nm

1 10 100 1000dN

/dlo

g(Dp)

/ cm

-3103

104

105

106

channelledrecirculation

Recirculation caused by perpendicular approach flow (>40 from canyon axis)

Extra particles in ‘fresh exhaust’ size range

0

5

10

15

20

25

30

35

90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270

wind direction

mea

sure

d N

0.1 /

bac

kgro

un

d N

0.1

Effect of sheltering on concentration enhancement

Main measurement site

0270

90

180

Statistical variation in ultra-fine concentrations

N0.1/cm-3

1x103 10x103 100x103 1x106

n i/ntotal

0.00

0.05

0.10

0.15

0.20

channelledrecirculated

N0.1 / cm-3

1000 10000 100000

Cum

f

0.0

0.2

0.4

0.6

0.8

1.0channelledrecirculatedbackground

Roughly log-normal concentration distributions

Comparison with background N0.1

N0.1 / cm-3

1000 10000 100000

Cum

f

0.0

0.2

0.4

0.6

0.8

1.0

street canyonbackground

N0.1 / cm-3 Street canyon Background Ratio

mean 26 500 6 000 4.5

Rush-hour mean 35 000 7 300 4.8

98.5th percentile (1 hr)

122 000 12 750 9.5

Influence of average daily exposure

• 23 hours background of 6 000 cm-3

• 1 hour (peak traffic period) canyon exposure at 35 000 cm-3

• Assume no other significant residential or occupational exposures

Background:

80 %

Canyon: 20 %

•average breathing rates are 2 – 3 times higher in streets, deposition deeper

•Exposure ratio street canyon:background may be 10 –20

Long-term exposure to UFP is dominated by a well-mixed urban background concentration.

Exposure is enhanced by short-term peaks at traffic-influenced locations.

Total personal exposure influenced by duration of proximity to traffic especially in street canyons.

Diurnal and longer-term variations in concentrations controlled by the ventilation rate of the city and hence by the thermal climate.

High morning peaks in UFP can occur when rush-hour begins before significant urban thermal emission, more likely at high latitudes in winter.

Within ~ 100 m of traffic sources meandering plumes make a small contribution to long-term means but a large contribution to upper percentile concentrations

Conclusions

Exposure in street canyons dominated by fresh plumes. Ventilation of streets is reduced by flow isolation.

Short, high doses may make a small contribution to total exposure, but can be highly significant in triggering ill-health.

Significance of street exposure greater for occupational exposure or leisure activities (e.g. street cafes).

PM10 does not capture the strong gradients in UFP, or the short-term variability.

Interventions (e.g. street closure) may have minor effect on modelled PM10, but potentially major reductions in UFP.

Conclusions

With thanks to

Cassella Stanger, London, UKCentre for Ecology and Hydrology, Edinburgh, UK

CERC Ltd., Cambridge, UK

Acknowledgements