1. UFP  PARTICLE NUMBER (ToN)
Emissions, Dynamics and Dispersion of Ultrafine Particles in Polluted Air (extract from doctoral thesis by Lars Gidhagen)
traffic exhaust particles
microenvironments: a) car tunnel b) street canyon c) close to a highway
urban scale
UFP  PARTICLE NUMBER (ToN)  
SO2
-pinene
1. How many particles are emitted by each vehicle?
2. What processes will affect the
ambient air concentrations?
3. What processes are of importance for
particle number concentrations on the urban scale?
Introduction
(WHO)

2. Diesel soot particles low density (decreasing with size)
Vehicle emissions
Diesel soot particles
low density (decreasing with size)
(Van Gulijk et al., 2004 )
tailpipe
Inital dilution/particle formation zone
(dilution ratio ~ )
soot particles (agglomerates): nm
Nanoparticles: < 50 nm
Subgrid (emission factor)
Simulated in aerosol model
nanoparticles contribute to > 90% of particle number
most of them are liquid (possibly solid core)
low concentrations of soot => more nanoparticles
low ambient temperature => more nanoparticles

3. lung deposition number surface area mass number surface area mass
Urban aerosol
nanoparticles
< 50 nm
ultrafine mode nm
fine mode m
coarse mode m
number
surface
area
mass
lung deposition
number
surface
area
mass
(Kittelson, 2004

4. Brownian motion makes nanoparticles collide with….
Removal processes
Brownian motion makes nanoparticles collide with….
particle nm
Intermodal coagulation
Intramodal coagulation
…. other particles: Coagulation
quasi-laminar
layer
turbulent diffusion
…. surfaces: Dry deposition
Effective reduction of nanoparticles if concentrations of larger particles are high
Effective reduction of nanoparticles if the turbulent transport towards the surface is fast

5. ==> 30 % removal of total particle number concentrations
97%
Car tunnel
(PAPER I)
veh/day
ToN: up to cm-3
Remaining particles at tunnel exit (rush hour conditions)
23%
59%
84%
97%
==> 30 % removal of total particle number concentrations

6. 2 ms-1 Fraction removed due to coagulation and dry deposition
Street canyon
(PAPER II)
coag + dep: 27% only coag: 15%
Fraction removed due to coagulation and dry deposition
ToN removal as compared to inert particles from
source A
2 ms-1 B A C
veh/day
ToN: up to cm-3
coag + dep: 5%
only coag: 6% A B
Most of the removal occurs close to the vehicles
Deposition is enhanced by vehicle movements (insensitive to wind speed)
coag + dep: 7%
only coag: 7% C
coag + dep: 27% only coag: 15%
Coagulation is only important during low wind speed conditions

7. slow but continuously working coagulation
Highway
(PAPER III)
veh/day
ToN: up to cm-3
Limited removal over the road, almost no removal for the dispersion ~ 100 m downwind
intense deposition
(~10%)
slow but continuously working coagulation
(<1%)
wind

8. Coagulation unimportant for average ToN concentrations
Urban scale
(PAPER IV)
Roof level (25 m)
Evaluation of simulated particle number concentrations against measurements
Removal in % due to coagulation
(compared to only dilution)
2.5-3
1.5-2
1-1.5
Average particle number (ToN) concentrations April 17-27, 2002
>15000
background ~ 3000
# cm-3
Removal in % due to dry deposition
(compared to only dilution)
20-25
>15
10-15
5-10
15-20
The results show that particle number can be simulated in urban models, in a similar way to particle mass or gaseous pollutants
Tower (100 m)
Coagulation unimportant for average ToN concentrations
Dry deposition important on the urban scale

9. ! ! ! Principal results    Outlook
Vehicle ToN emission factors for urban modeling 
Particle number / urban scale: - Dry deposition important Coagulation of little importantance 
Particle number can be simulated over large cities 
Outlook !
Verify size distribution on urban scale
Verify model in larger / “warmer” city !
Extend model to national scale !

10. Finis