Study On Characterization And Emission Factors Of NanoParticles From Vehicles

The objective of this paper was to characterize nanoparticles emissions from vehicles in street canyon. The study was focused on determining on-road nanoparticles number concentrations, and estimating particle emission factors. Data were collected in Hornsgatan street and in residential areas 600m away from the street. Simultaneous measurements of particle size distribution (size range 7-400 nm) inside an urban street canyon and a nearby Rosenlundsgatan urban background location in Stockholm in June 2002-January 2003 were used to separate the traffic source contribution in the street canyon from the background levels.Much lower number concentrations and larger particles were observed at roof station. The background concentrations are not highly variable and showing a diurnal variation pattern similar to street concentrations, but with a several times smaller amplitude. The average ratio background/street concentration is 0.19 for total particle number (ToN), and 0.17,0.34, respectively, for NO_x and CO.The correlation between NO_x, CO and total particle number (ToN) measurements at the street location is obvious. The wind speed (WS) and wind directions (WD) influence all parameters in a similar way. The vehicle pollutants diurnal pattern is synchronized with traffic volume diurnal cycles. The diurnal variation pattern on Saturdays is similar to Sundays.Most of the particles added by the on-road fleet were below 50nm in diameter. Particles in this size range may dominate particle number, but contribute little to particle volume or mass. The particle number concentration size distribution of the traffic source shows a maximum at particle sizes of 15-25nm independent of the changing heavy-duty vehicle share and time.Using OSPM model, the method of inverse modelling was applied to estimate average fleet particle number emission factors typical of urban conditions in Stockholm. All vehicles that pass through Hornsgatan street were divided into light duty vehicles (LDV) and heavy duty vehicles (HDV). Emission factors of particle number per average vehicle were estimated as (8.26±0.08)×10¹⁴ particles/km, and multiple regression method determined emission factors are (5.13±0.38)×10¹⁴ particles/km, (93.08×10¹⁴ particles/km, respectively, for LDV and HDV. On average, one HDV emits a 15～22 times higher amount of particulate air pollutants than one LDV, that is the magnitude of emission factor of HDV is an order larger than that of LDV. They are in good agreement with Imhof's results of "On average, one HDV' particle number emission factors is 10～30 times higher than that of one LDV".The estimated particle emission factors are compared with other published data. The particle number emission factors in this study for an average vehicle fleet and light-duty vehicles are very close to other published data, whilst those for heavy-duty vehicles are higher than in the comparable studies. Despite many differences in the design and implementation of the various studies, the results for particulate matter are broadly similar, they are in the same order.