1. Wear and Resuspension Particles
from Road Traffic
Sources and Emission Factors
Robert Gehrig, Nicolas Bukowiecki
EMPA Dübendorf (Switzerland)
Urban Air Quality: The Challenge of Non-Exhaust Emissions from Traffic
Sources, Health Risks and Mitigation; Barcelona, Spain July 11-12, 2013

2. Materials Science & Technolog y
Outline
 Emission factors from Swiss field campaigns
 Road wear or resuspension?
 Tyre wear
 Conclusions
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

3. Materials Science & Technolog y
Non-exhaust sources
 Brake wear
 Road wear
 Resuspension of road dust
 Tyre wear
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

4. Materials Science & Technolog y
Motorway in Rural Area (Reiden LU)
Measuring
Site 1
Wind Direction
Road
Background +
Traffic Emssions Background Only
Measuring
Site 2
50’000 vehicles per day
Rural Motorway
120 km/h free-flowing
HDV Fraction 15%
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013
cx, motorway traffic = cx, downwind – cx, upwind

5. Materials Science & Technolog y
Motorway in Rural Area (Reiden LU)
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

6. Materials Science & Technolog y
Street Canyon (Zürich Weststrasse)
22’000 vehicles per day
Measuring Site 1
Road
Background Only
Measuring Site 2
Urban Traffic
Background
Background +
Traffic Emssions
Urban Street Canyon
Stop and Go Traffic
HDV Fraction 10%
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013
cx, local traffic = cx, street canyon – cx, urban background

7. Materials Science & Technolog y
Street Canyon (Zürich Weststrasse)
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

8. Materials Science & Technolog y
The Empa Rotating Drum Impactor (RDI)
Bukowiecki et al. , Environmental Science and Technology (2005) 39, 5754-5762
Lundgren, D. , J. Air Pollut. Control Assoc. (1969) 17, 225-229.
• Size fractionation by
rectangular nozzles
• Aluminum wheels
• Substrate: 6 μm PP
• Bouncing prevention:
Apiezon M
1 bar = 1 hour
1 wheel = 4 days
~10 µg total aerosol mass
per spot
The Empa RDI is a modification of the original Lundgren impactor:
1.52 x 10 mm
0.68 x 10 mm
0.30 x 10 mm
1.52 x 10 mm
0.68 x 10 mm
0.30 x 10 mm
backup filter for
ultrafine fraction
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

9. Materials Science & Technolog y
Concentrations of PM10 and Antimony
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

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Calculation of Emission Factors
Concentration differences
Traffic counts (LDV, HDV) Emission factors
Dilution (from NOx)
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

11. Materials Science & Technolog y
Emission factors for selected elements
Relative size distribution (Sum=1):
(HDV)
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013
LDV
HDV

12. Materials Science & Technolog y
PM10 Emission factors Zürich-Weststrasse
Zürich-Weststrasse:
Urban Street Canyon
Stop and Go Traffic
HDV Fraction 10%
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

13. Materials Science & Technolog y
PM10 Emission factors Reiden
Reiden:
Rural Main Freeway
120 km/h free-flowing
HDV Fraction 20%
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

14. Materials Science & Technolog y
Can this be modelled?
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

15. Materials Science & Technolog y
 Emission factors from Swiss field campaigns
 Road wear or resuspension?
 Tyre wear
 Conclusions
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

16. Materials Science & Technolog y
How a Mobile Load Simulator works
2400mm
1200mm
940mm
300mm
MMLSMMLS
Model Mobile Load Simulator
Ø
2400mm
1200mm
940mm
300mm
MMLSMMLS
Model Mobile Load Simulator
Ø
direction of moving wheel
and induced air stream
sampling point for dosing of
particles and tracer gas tracer gas
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

17. Materials Science & Technolog y
MMLS in operation
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

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View of MLS
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

19. Materials Science & Technolog y
View of MLS
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

20. Materials Science & Technolog y
Preparation of the test surface
porous asphalt
asphalt concrete
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

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Typical mass size distribution
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.1 1 10 100
aerodynamic particle diameter (µm)
dM/dlogDp
Ambient air
Simulator in operation
Difference (= abraded fraction)
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

22. Materials Science & Technolog y
Abrasion from asphalt concrete pavement
0.00
0.05
0.10
0.15
0.20
0.25
0.30 -24
-12
0
12
24
36
48
60
72
84
96
108
120
132
144
156
168
180
min
PM10(µg/m3
)
Red: ambient air concentration
Black: MMLS in operation
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

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PM10 emission factors for fresh particle abrasion
Type of mobile load simulator
MMLS
(LDV)
MMLS
(LDV)
MLS
(HDV)
MLS
(HDV)
Type of pavement
asphalt
concrete
porous
asphalt
asphalt
concrete
asphalt
concrete
Condition of pavement new new good poor
PM10 emission factor
(mg/km/wheel)
0.25 0 – 0.2 0.7 8
PM10 emission factor (mg/km/LDV) 3 0 - 2
PM10 emission factor (mg/km/HDV) 7 80
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

24. Materials Science & Technolog y
PM10 emission factors for resuspension
Type of mobile load simulator
MMLS
(LDV)
MMLS
(LDV)
MLS
(HDV)
MLS
(HDV)
Type of pavement
asphalt
concrete
porous
asphalt
asphalt
concrete
asphalt
concrete
Condition of pavement new new good poor
PM10 emission factor (mg/km/wheel) 6.3 0.41 11 66
PM10 emission factor (mg/km/LDV) 76 5
PM10 emission factor (mg/km/HDV) 110 660
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

25. Materials Science & Technolog y
Resuspension of dust
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013
0
100
200
300
400
500
600
700
0 20 40 60 80
mg/km
min
porous asphalt
asphalt concrete

26. Materials Science & Technolog y
Resuspension of dust (detail view)
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013
0
5
10
15
20
25
30
35
40
45
50
0 10 20 30 40 50 60 70
mg/km
min
porous asphalt
asphalt concrete

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 Emission factors from Swiss field campaigns
 Road wear or resuspension?
 Tyre wear
 Conclusions
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

28. Materials Science & Technolog y
PM10- emission factors for Fe and Zn
MLS-Messungen (HDV) Fe Zn
Tyre
(1% Zn)
Simulator in operation (µg·m-3) 1.68 0.129 12.9
Ambient air (µg·m-3) 0.32 0.008 0.8
Difference (metal abrasion, (µg·m-3) 1.36 0.121 12.1
Emission factor per HDV (mg·km-1) 1.91 0.17 17
MMLS-Messungen (LDV) Fe Zn
Tyre
(1% Zn)
Total concentration (µg·m-3) 1 0.02 2.0
Emission factor per LDV (mg·km-1) 0.40 0.008 0.80
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

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Tyre wear particles in PM10
Julie M. Panko et al.; Atmospheric Environment 72 (2013) 192-199
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

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% Tyre wear in PM
(Günter Stein et al. VDI 2009)
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

31. Materials Science & Technolog y
Tyre abrasion
Photo: V. Dietze, Deutscher Wetterdienst, Referat Lufthygiene Freiburg i.Br.(D)
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

32. Materials Science & Technolog y
Conclusions
 Abrasion related particles and resuspended road dust were mainly found in
the 1-10 µm particle size range.
 In the street canyon and along the motorway, abrasion sources and vehicle
induced dust resuspension made up about 50% of the traffic related PM10
emissions.
 Brake wear and resuspension were found to be more mass relevant in the
street canyon than road wear and tire wear.
 Road wear was found to be of minor importance for intact pavements, but
damaged pavements can lead to substantial road wear emissions.
 Vehicle induced resuspension is not strictly correlated with traffic numbers
but is strongly influenced by available road dust. Difficult to describe with
conventional emission factor models.
 Tyre wear seems to be of minor importance.
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013

33. Materials Science & Technolog y
Acknowledgements
We thank for the financial support by:
 Swiss Federal Roads Office (ASTRA)
 Swiss Federal Office for the Environment (FOEN)
R. Gehrig; International Workshop Urban Air Quality, Barcelona, July 2013