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Emissions, Dynamics and Dispersion of Ultrafine Particles in Polluted Air (extract from doctoral thesis by Lars Gidhagen). UFP  PARTICLE NUMBER (ToN). -pinene. traffic exhaust particles microenvironments: a) car tunnel b) street canyon c) close to a highway

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

  2. Diesel soot particles • nanoparticles contribute to > 90% of particle number Subgrid (emission factor) Simulated in aerosol model • low density (decreasing with size) tailpipe Inital dilution/particle formation zone (dilution ratio ~ 5 - 50) soot particles (agglomerates): 40-300 nm • most of them are liquid (possibly solid core) • low concentrations of soot => more nanoparticles Nanoparticles: < 50 nm • low ambient temperature => more nanoparticles (Van Gulijk et al., 2004 ) Vehicle emissions

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

  4. …. other particles: Coagulation …. surfaces: Dry deposition Intermodal coagulation Intramodal coagulation turbulent diffusion particle 100-200 nm quasi-laminar layer Removal processes Brownian motion makes nanoparticles collide with…. • 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. 97% Remaining particles at tunnel exit (rush hour conditions) 97% 84% 59% 23% ==> 30 % removal of total particle number concentrations Car tunnel (PAPER I) • 36 000 veh/day • ToN: up to 1 300 000 cm-3

  6. Fraction removed due to coagulation and dry deposition 2 ms-1 B coag + dep: 5% only coag: 6% coag + dep: 7% only coag: 7% coag + dep: 27% only coag: 15% C A ToN removal as compared to inert particles from source A A B C Street canyon (PAPER II) • 35 500 veh/day • ToN: up to 210 000 cm-3 • Most of the removal occurs close to the vehicles • Deposition is enhanced by vehicle movements (insensitive to wind speed) coag + dep: 27% only coag: 15% • Coagulation is only important during low wind speed conditions

  7. slow but continuously working coagulation (<1%) intense deposition (~10%) wind Highway (PAPER III) Limited removal over the road, almost no removal for the dispersion ~ 100 m downwind • 52 300 veh/day • ToN: up to 70 000 cm-3

  8. Evaluation of simulated particle number concentrations against measurements 120 000 20-25 Roof level (25 m) 2.5-3 # cm-3 1.5-2 20-25 Average particle number (ToN) concentrations April 17-27, 2002 background ~ 3000 15-20 >15 1-1.5 10-15 >15000 Tower (100 m) 5-10 Removal in % due to dry deposition (compared to only dilution) Removal in % due to coagulation (compared to only dilution) • Coagulation unimportant for average ToN concentrations • Dry deposition important on the urban scale Urban scale (PAPER IV) The results show that particle number can be simulated in urban models, in a similar way to particle mass or gaseous pollutants

  9. 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 ! ! ! Principal results

  10. Finis

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