Ian Longley

Physics Department, UMIST, Manchester, U.K.

Fine scale temporal variation in ultrafine particle concentrations in a busy street canyon

with consequences for human exposure

PM10 and ultrafine particles (UFP)

• PM10 linked by epidemiology to poor health• Plausible toxicological mechanisms for UFP• PM10 influenced by advection and

resuspension – small spatial variation in urban areas

Excursions and street canyon exposure

• Experiments on rats show greater effect if dose delivered in short bursts (Michaels & Kleinman, 2000)

• Personal exposure of typical person uneven over the day – excursions associated with commuting.

• Hot spot/background ratio much higher for UFP than PM10

• High, sudden UFP exposures could trigger exacerbations and cardiovascular events

SW perp

Up-canyon

NE perp

Down-canyon

Measurement site

SCAR – Princess Street, Manchester

One-way traffic

Up to 1100 h-1

Including buses

•SMPS (TSI 3080 + nano DMA)

•20 Hz sonic anemometers

•2 weeks of measurements, 24 hours a day, Mon-Fri

SCAR measurements

Longley et al., 2003, Atmos. Env. 37, 1563-1571.

SCAR-4 Mean street-level aerosol mass size distribution

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

all SCAR-4 mean

02:00-03:00, 17th15:00-16:00, 18th

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+6all SCAR-4 mean

02:00-03:00, 17th15:00-16:00, 18th

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+6all SCAR-4 mean

02:00-03:00, 17th15:00-16:00, 18th

N0.1 Ultrafine particle concentration

Parallel flow

Perpendicular flow

Wind speed above and within canyon unrelated

Ultrafine N0.1 (Dp<0.1m) concentrationsParallel flow with channelling

10-minute means

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

200000

0 1 2 3 4

U / ms-1

N0

.1 /

cm

-3

daynight

Perpendicular flow with channelling

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

200000

0 1 2 3 4

U / ms-1

N0

.1 /

cm

-3

daynight

Perpendicular flow with recirculation

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

200000

0 1 2 3 4

U / ms-1

N0

.1 /

cm

-3

daynightrecirculation

Ultrafines number size distribution and in-canyon meteorology

Dp / nm

1 10 100 1000dN

/dlo

g(Dp)

/ c

m-3

103

104

105

106

channelledrecirculationmean

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

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

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 canyon, deposition deeper

•Exposure ratio canyon:background may be 10 –20

Concentrations of UFP in canyon typically 4.5 times higher than in urban background.

Concentrations dependent upon wind direction.

Perpendicular flow can lead to recirculation. Concentrations on lee side of canyon in the range of 30 000 – 150 000 cm-3, i.e. an order of magnitude greater than the background.

Concentrations inversely related to wind speed in the canyon, BUT recirculation also breaks link between wind speed in canyon and aloft.

A person exposed to background for 23 hours and street canyon for 1 (peak) hour receives 20% of exposure in 4% of time.

Brief but very high exposure to ultrafines - high risk to vulnerable individuals, not captured in current regulation of PM10.

Conclusions

With thanks to Martin Gallagher, Mike Flynn, James Dorsey, Paul

Williams, Rami Alfarra, James Allan,Mike Cubison, Keith Bower, Karl Beswick, Gordon

McFiggans, Tom Choularton(UMIST)

plusCERC Ltd., Cambridge, UK

Acknowledgements