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)

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 ~ 5 - 50) soot particles (agglomerates): 40-300 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

lung deposition number surface area mass number surface area mass Urban aerosol nanoparticles < 50 nm ultrafine mode 3 - 100 nm fine mode 0.1 - 2.5 m coarse mode 2.5 - 10 m number surface area mass lung deposition number surface area mass (Kittelson, 2004

Brownian motion makes nanoparticles collide with…. Removal processes Brownian motion makes nanoparticles collide with…. particle 100-200 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

==> 30 % removal of total particle number concentrations 97% Car tunnel (PAPER I) 36 000 veh/day ToN: up to 1 300 000 cm-3 Remaining particles at tunnel exit (rush hour conditions) 23% 59% 84% 97% ==> 30 % removal of total particle number concentrations

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 35 500 veh/day ToN: up to 210 000 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

slow but continuously working coagulation Highway (PAPER III) 52 300 veh/day ToN: up to 70 000 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

Coagulation unimportant for average ToN concentrations Urban scale (PAPER IV) Roof level (25 m) Evaluation of simulated particle number concentrations against measurements 120 000 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

! ! ! 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 !

Finis