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Microscale variations of atmospheric particle number size distributions
in a densely built-up city area
M. Merkel (1), W. Birmili (1), A. Wiedensohler (1), D. Hinneburg (1), O. Knoth (1), T. Tuch (2,1) and U. Franck (2)
(1) Leibniz Institute for Tropospheric Research, Permoserstr. 15, 04318 Leipzig, Germany
(2) UFZ – Helmholtz-Centre for Environmental Research, Permoserstr. 15, 04318 Leipzig, Germany
Email: merkel@tropos.de
Leibniz Institute for Tropospheric Research - Physics Department, Aerosol Group
Instrumental set-up
Motivation
Spatial aerosol measurements during PURAT III and IV
Conclusions
This work was supported by UBA contract UFOPLAN No. 20442204/03
and the EU Marie Curie Reintegration Grant FP6-2002-Mobility-11
contract No. 510583.
• Urban submicron (< 1 μm) und ultrafine (< 0.1 μm) particles have
moved into the focus of public health interest because they are
suspected to contribute to acute and chronic disease in
susceptible parts of the population (HEI, 2002).
• The dominant source of aerosol particle number concentration in
urban areas is combustion of fossil fuel in motor vehicles. Particle
number size distributions near roads with high traffic are
dominated by particles smaller than 100 nm in diameter.
• To investigate the spatially-resolved exposure of the population to
these particles, fundamental knowledge about the spatial and
temporal variability of fine und ultrafine particles in the urban
atmosphere is needed.
• A field experiment (PURAT*) was conducted to investigate the
spatial
and
temporal
variability of
fine
and
ultrafine aerosol particles
in the microscale environment around the street canyon Eisenbahnstraße
in Leipzig, Germany.
• Continuous measurements with TDMPS and SMPS systems
• PURAT III: three sites (1,2,3) in winter 2005/2006
• PURAT IV: four sites (1,2,3,4) in July and August 2006
• The measurements of aerosols were supplemented by:
roof level wind direction and wind speed
manual and automatic traffic counts
nitrogen oxides at the roof-top and the street canyon
particle number size distributions at a reference background station (“IfT”), 2 km northeast
*
PURAT - Particles in the urban atmosphere: Behaviour of fine and ultrafine particles, their spatial variation and relationships with local policy action
References
general trend in particle number concentration:
urban background ≈ courtyard < roof-top < street canyon <
sidewalk
ultrafine particles are distributed very inhomogeneously
the
measured concentrations were strongly influenced by the
wind direction inside the street canyon
the
dominating process affecting the dispersing aerosol is dilution
with ambient air, coagulation and condensation are playing only a
minor role in microscale transports (the half-lifetime of a 12 nm-
particle against coagulation is about 40 minutes)
qualitative
agreement between measured data and the results of
the three-dimensional dispersion model ASAM (Hinneburg and
Knoth, 2005)
1 street canyon
(first floor)
2 roof-top
3 courtyard
Sketch of the atmospheric air flow in the vicinity of
the street canyon “Eisenbahnstraße” in Leipzig
4 sidewalk
HEI (2002), Understanding the health effects of components of the particular matter
mix: progress and next steps. Health Effects Institute, 4, Boston, MA
J. Voigtländer, T. Tuch, W. Birmili, A. Wiedensohler (2006) Correlation between
traffic density and particle size distribution in a street canyon and the dependence
on wind direction.
Atmos. Chem. Phys.
6
:4275-4286, 2006
B. Wehner, W. Birmili, T. Gnauk and A. Wiedensohler (2002) Particle number size
distributions in a street canyon and their transformation into the urban-air
background: measurements and a simple model study.
Atmospheric Environment
,
36
: 2215-2223
Differences between the measurement sites
1 street canyon
Simulation results with ASAM: normalized concentrations and
flow field for various wind directions (top view)
3D-Simulations
PURAT III
PURAT IV
0 2 4 6 8 10 12 14 16 18 20 22 24
3
10
100
800
3
courtyard
particle diameter in nm
0 2 4 6 8 10 12 14 16 18 20 22 24
10
100
800
roof-top
particle diameter in nm
0 2 4 6 8 10 12 14 16 18 20 22 24
3
10
100
800
street canyon
particle diameter in nm
0 2 4 6 8 10 12 14 16 18 20 22 24
3
10
100
800
d
N
/ dlog
D
p
, cm
-3
urban background (IfT)
particle diameter in nm
200.0
321.2
517.0
832.4
1337
2152
3464
5563
8955 1.442E4 2.315E4 3.727E4
6E4
1
10
100
1000
10
100
1000
10000
2.00-4.00 am
dN/dlogDp [cm
-3
]
Dp [nm]
1
10
100
1000
10
100
1000
10000
6.00-8.00 am
dN/dlogDp [cm
-3
]
Dp [nm]
street canyon
roof-top
courtyard
urban background (IfT)
1
10
100
1000
100
1000
10000
6.30-10.00 am
dN/dlogDp [cm
-3
]
Dp [nm]
sidewalk
street canyon
roof-top
urban background
0
6
12
18
24
0
10000
20000
30000
40000
sidewalk/courtyard
street canyon
roof-top
urban background
N (10-500 nm)
cm
-3
time of day (h)
Total concentrations and diurnal variations
Distribution of wind direction
(yellow) and wind velocity (red) in
Average wind distribution of
connection with local topography
number concentrations
Median particle number size distributions for day times with low (left)
and high traffic volume (right)
Mean number size distributions and diurnal profiles (N[10-500 nm])
rush-hour
traffic
no traffic
N ≈ 13000 cm
-3
N ≈7000 cm
-3
N ≈5000 cm
-3
N ≈25000 cm
-3
1
2
3
back-
ground
Measured vs. simulated particle concentration for
changing wind directions and wind speeds
0
10000
20000
30000
0
30
60
90
120
150
180
210
240
270
300
330
0
10000
20000
30000
N(15-800 nm)
street canyon
roof-top
courtyard
background
330
335
340
345
350
355
0
350
700
wind speed
cm s
-1
Julian day of the year 2005
0
90
180
270
360
wind direction
degree
0
8000
16000
cm
-3
0
60000
120000
measured
simulated
roof-top
street canyon
cm
-3
CPC-3007 measurements
219.296
219.298
219.300
219.302
219.304
0
50000
100000
150000
cm
-3
Julian day of the year 2006
sidewalk
entrance