Change search
ReferencesLink to record
Permanent link

Direct link
Simulation of NOx and ultrafine particles in a street canyon in Stockholm, Sweden
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
2004 (English)In: Atmospheric Environment, ISSN 1352-2310, Vol. 38, no 14Article in journal (Refereed) Published
Abstract [en]

A computational fluid dynamic (CFD) model has been used to assess the concentrations of NOx and particle number in a street canyon in Stockholm with a high traffic volume. Comparisons of a simulated 11-week long time series of NOx with measurements (both sides of the street, urban background excluded) show good agreement, especially if emissions are distributed to be three times higher along the side of the street where the traffic is uphill, as compared to the downhill side. The simulation of number concentrations of inert particles indicates a similar asymmetry in emissions.

A month-long measurement of particle size distribution (7–450 nm) at street level indicates that the ratio of nucleation size mode particle (7–20 nm) to total particle number (7–450 nm) is decreasing for increased particle surface area. Given the strong dominance of the locally generated particles over the urban background, this is interpreted as a local change in the size distribution. The results of a monodisperse aerosol dynamic model, coupled to the CFD model that simulates also the turbulence generated by vehicle movements, show that coagulation and deposition may reduce total particle inside the canyon with approximately 30% during low wind speeds. Most of the removal occurs shortly after emission, before the particles reach the leeward curb-side. Losses between the leeward curb-side and other locations in the street, e.g. roof levels, is estimated to be smaller, less than 10%. Coagulation is the dominating removal process under low wind speed conditions and deposition for higher wind speeds, the summed removal being smaller for high wind velocities. Deposition is enhanced over the road surface due to the velocities generated by vehicle movements. Although coagulation and deposition removal is most effective on the smallest ultrafine particles, this effect is not sufficient to explain the observed change in size distribution. It is suggested that also the formation of particles in the exhaust plumes is influenced by a larger particle surface area in the ambient air.

Place, publisher, year, edition, pages
2004. Vol. 38, no 14
Keyword [en]
Aerosol model; CFD model; Traffic produced turbulence; Vehicle emissions; Emission factor; Measurements
National Category
Meteorology and Atmospheric Sciences
URN: urn:nbn:se:su:diva-23771DOI: 10.1016/j.atmosenv.2004.02.014OAI: diva2:194433
Part of urn:nbn:se:su:diva-48Available from: 2004-02-10 Created: 2004-02-10 Last updated: 2010-08-02Bibliographically approved
In thesis
1. Emissions, dynamics and dispersion of particles in polluted air
Open this publication in new window or tab >>Emissions, dynamics and dispersion of particles in polluted air
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The main objective of this thesis is to yield information on how atmospheric fine and ultrafine particles are dispersed in populated areas. Quantitative information on emissions, transport and removal is needed to assess the health risks of inhalable particles. Most effort is dedicated to describe, on the local and urban scales, the distribution of ultrafine particles (and thereby also total number concentrations) originating from traffic emissions. A minor part addresses the dispersion of toxic particles of industrial origin, dispersed over regional scales. The importance of aerosol dynamics for the distribution of ultrafine particles is assessed by coupling a three-dimensional dispersion model to a monodisperse aerosol model. Meteorological forcing, sometimes in a complex geometry, is simulated by a CFD model on the local scale and by a weather forecast model on the larger scales.

The principal result of the study is that particle number concentrations can, at least for Swedish conditions, be simulated and quantitatively assessed in urban models in a similar way as particle mass or gaseous pollutants. The variability of the emissions and the removal effects of coagulation and dry deposition are investigated. Vehicle emissions of particle number vary with a factor of two depending on ambient temperature, with higher concentrations during cold conditions. Other important factors that determine particle emissions are fleet composition, vehicle speed (especially for gasoline-fueled cars) and the dilution rate in the microenvironment where emissions take place. Coagulation affects particle number concentrations in highly polluted environments like car tunnels or street canyons under low wind speed conditions, while it is of less importance in the urban background (reduced number concentrations of a few percent, as compared to completely inert particles). Dry deposition is effective over the road surface, due to the velocities and turbulence produced by moving vehicles. Dry deposition also has significant effects on the urban background concentrations, reducing average levels with up to 20-30%. Dry deposition is also shown to be an important mechanism to remove fine particulate mass on the regional scale.

Simulated particle number concentrations, based on emission factors determined for the local vehicle fleet and influenced by aerosol dynamic processes, are evaluated against measured concentrations for three different traffic microenvironments and also for the entire Stockholm area. Regional dispersion of arsenic in PM10 is assessed and model results compared to measurements in Central and Northern Chile.

Place, publisher, year, edition, pages
Stockholm: Meteorologiska institutionen (MISU), 2004. 154 p.
National Category
Meteorology and Atmospheric Sciences
urn:nbn:se:su:diva-48 (URN)91-7265-808-8 (ISBN)
Public defence
2004-03-05, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 12 A, Stockholm, 13:00 (English)
Available from: 2004-02-10 Created: 2004-02-10 Last updated: 2009-05-28Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full text

Search in DiVA

By author/editor
Johansson, Christer
By organisation
Department of Meteorology Department of Applied Environmental Science (ITM)
In the same journal
Atmospheric Environment
Meteorology and Atmospheric Sciences

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 110 hits
ReferencesLink to record
Permanent link

Direct link