i.d. longley, j.r. dorsey, m.w. gallagher, j.d. allan, m.r. alfarra, h.coe physics department,...
TRANSCRIPT
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