Description of the OSPM model

OSPM is a practical street pollution model, developed by the Department of Environmental Science at Aarhus University (the former National Environmental Research Institute, Department of Atmospheric Environment).

Description of the dispersion parameterisation in OSPM

Concentrations of exhaust gases are calculated using a combination of a plume model for the direct contribution and a box model for the recirculating part of the pollutants in the street.

The direct contribution is calculated using a simple plume model. It is assumed that both the traffic and emissions are uniformly distributed across the canyon. The emission field is treated as a number of infinitesimal line sources aligned perpendicular to the wind direction at the street level. The cross wind diffusion is disregarded. The wind direction at the street level is assumed to be mirror reflected with respect to the roof level wind. The plume expression for a line source is integrated along the path defined by the street level wind. The length of the integration path depends on the extension of the recirculation zone.

  • The length of the vortex, calculated along the wind direction, is 2 x the upwind building height. For roof-level wind speeds below 2 m/s, the length of the vortex decreases linearly with the wind speed. The buildings along the street may have different heights, affecting thereby the length of the vortex and subsequently the modelled concentrations.
  • The upwind receptor (lee-side) receives contribution from the traffic emissions within the area occupied by the vortex (the recirculation zone), the recirculated pollution and a portion of the emissions from outside of the vortex area.
  • The downwind receptor (wind-side) receives contributions from the recirculated pollution and the traffic emissions from outside of the recirculation zone only.
  • As the wind speed approaches zero or is parallel with the street, concentrations on the both sides of the street became equal.
  • The vertical dispersion is modelled assuming a linear growth of the plume with the distance from the source.

Vertical dispersion:

The direct contribution:

Initial disperison:

ho = 2~4 m (depends on wind speed)

The contribution from the recirculation part is calculated using a simple box model. It is assumed that the canyon vortex has the shape of a trapeze, with the maximum length of the upper edge being half of the vortex length. The ventilation of the recirculation zone takes place through the edges of the trapeze but the ventilation can be limited by the presence of a downwind building if the building intercepts one of the edges. The concentration in the recirculation zone is calculated assuming that the inflow rate of the pollutants into the recirculation zone is equal to the outflow rate and that the pollutants are well mixed inside the zone.

Traffic Produced Turbulence (TPT)

The turbulence within the canyon is calculated taking into account the traffic produced turbulence. The TPT plays a crucial role in determination of pollution levels in street canyons. During windless conditions the ambient turbulence vanishes and the only dispersion mechanism is due to the TPT. Thereby, the TPT becomes the critical factor determining the highest pollution levels in a street canyon.

Street geometry

The model can be used for streets with irregular buildings or even buildings on one side only but it is best suited for regular street-canyon configurations. The model should not be used for crossings or for locations far away from the traffic lanes.

Wind meandering

Concentration distribution of pollutants in the street is calculated taking into account wind direction fluctuations. For each calculation hour, the resulting concentrations are averaged over a wind direction sector centered arround the hourly mean wind direction. The width of the averaging wind sector depends on the roof level wind speed and increases with the decreasing wind speed. For calm conditions the averaging sector approaches 360o, which results in uniform concentration distribution accross the street.

NO2 chemistry

The NO2 concentrations are calculated taking into account NO-NO2-O3 chemistry and the residence time of pollutants in the street.

The presence of NO2 in ambient air is mainly due to the chemical oxidation of the emitted NO by background ozone. Under sunlight conditions, photodissociation of NO2 leads to partial reproduction of NO and O3.

NO + O3 <=> NO2 + O2

The relationship between NO2 and NOx concentrations in the ambient air is non-linear and depends on the concentrations of ozone. The time scales characterising these reactions are of the order of tens of seconds, thus comparable with residence time of pollutants in a street canyon. Consequently, the chemical transformations and exchange of street canyon air with the ambient air are of importance for NO2 formation.

Model structure

The model is designed to work with input and output in the form of one-hour averages.

The required input data are hourly values of wind speed, wind direction, temperature and global radiation. The two last parameters are used for calculation of chemical transformation of NO-NO2-O3. The model requires also hourly values of urban background concentrations of the modelled pollutants. Beside the hourly input parameters, the model requires also the data on the street geometry and the traffic in the street.

Windows version

A newly developed Windows version of OSPM contains a user-friendly interface, which allows for online preparation of all the required input data and files. The Windows version, which is distributed under the name WinOSPM contains special modules for preparation and visualisation of traffic data and traffic emissions. An evaluation version of WinOSPM is available for download.

Literature

Note that the access to some online publications might be restricted.

  • Berkowicz, R. (1998) Street Scale Models, In J. Fenger, O. Hertel, and F. Palmgren (eds.), Urban Air Pollution - European Aspects, Kluwer Academic Publishers, pp. 223-251.
  • Berkowicz, R. (2000) OSPM - A parameterised street pollution model, Environmental Monitoring and Assessment, Volume 65, Issue 1/2, pp. 323-331.
  • Berkowicz, R., Hertel, O., Larsen, S.E., Sørensen, N.N. and Nielsen, M. (1997) Modelling traffic pollution in streets (report in PDF format, 850 kB).
  • Berkowicz, R., Hertel, O., Sørensen, N.N. and Michelsen, J.A. (1997) Modelling air pollution from traffic in urban areas, In R.J. Perkins and S.E. Belcher (eds), Flow and Dispersion Through Groups of Obstacles, pp 121-141, Clarendon Press, Oxford, pp 121-141.
  • Berkowicz, R., Ketzel, M., Vachon, G., Louka ,P., Rosant, J.-M., Mestayer, P.G. and Sini J-.F. (2002) Examination of Traffic Pollution Distribution in a Street Canyon Using the Nantes'99 Experimental Data and Comparison with Model Results, Water, Air and Soil Pollution: Focus 2(5), 311-324.
  • Di Sabatino, S., Kastner-Klein, P., Berkowicz, R., Britter, R. and Fedorovich, E. (2003) The modelling of turbulence from traffic in urban dispersion models – Part I: Theoretical considerations,Environmental Fluid Mechanics 3, 129–143.
  • Hertel, O. and Berkowicz, R. (1989a) Modelling pollution from traffic in a street canyon. Evaluation of data and model development, DMU Luft A-129, 77p.
  • Hertel, O. and Berkowicz, R. (1989b) Modelling NO2 concentrations in a street canyon, DMU Luft A-131, 31p.
  • Hertel, O. and Berkowicz, R. (1989c) Operational Street Pollution Model (OSPM). Evaluation of the model on data from St. Olavs street in Oslo, DMU Luft A-135.
  • Kastner-Klein, P., Fedorovich, E., Ketzel, M., Berkowicz, R. and Britter, R. (2003) The modelling of turbulence from traffic in urban dispersion models – Part II: Evaluation Against Laboratory and Full-Scale Concentration Measurements in Street Canyons, Environmental Fluid Mechanics 3, 145–172.
  • Ketzel, M., Berkowicz, R. and Lohmeyer, A. (2000) Comparison of Numerical Street Dispersion Models with Results from Wind Tunnel and Field Measurements, Environmental Monitoring and Assessment, Volume 65, Issue 1/2, pp. 363-370
  • Ketzel, M., Berkowicz, R., Lohmeyer, A., Kastner-Klein, P. and Flassak T. (2001) Adaptation of results from CFD-models and wind-tunnels for practical traffic pollution modelling. Presentation at 7th Int. Conf. on Harmonisation within Atmospheric Dispersion Modelling, Belgirate, Italy, 28-31 May 2001.
  • Ketzel, M., Berkowicz, R., Müller, W.J. and Lohmeyer, A. (2002) Dependence of street canyon concentrations on above roof wind speed - implications for numerical modelling. International Journal of Environment and Pollution 17, pp. 356-366
  • Ketzel M, Berkowicz R, Hvidberg M, Jensen SS and Raaschou-Nielsen O. (2011): Evaluation of AirGIS - a GIS-based air pollution and human exposure modelling system. International Journal of Environment and Pollution. Vol. 47, Nos. 1/2/3/4, pp. 226–238.(doi-Link)
  • Ketzel M, Jensen SS, Brandt J, Ellermann T, Olesen HR, Berkowicz R and Hertel O (2012): Evaluation of the Street Pollution Model OSPM for Measurements at 12 Streets Stations Using a Newly Developed and Freely Available Evaluation Tool. J Civil Environ Eng, S1:004.(doi-Link)
  • Kakosimos K.E., Hertel O., Ketzel M. and Berkowicz R. (2011): "Operational Street Pollution Model (OSPM) - a review of performed validation studies, and future prospects", Environmental Chemistry, 7, 485-503.(doi-Link)
  • Kukkonen, J., Valkonen, E., Walden, J., Koskentalo, T., Aarnio, P., Karppinen, A., Berkowicz, R. and Kartastenpää, R. (2000) A measurement campaign in a street canyon in Helsinki and comparison of results with predictions of the OSPM model, Atmospheric Environment 35, 231-243.
  • Kukkonen, J., Partanen, L., Karppinen, A., Walden, J., Kartastenpää, R., Aarnio, P., Koskentalo, T. and Berkowicz, R. (2003) Evaluation of the OSPM model combined with an urban background model against the data measured in 1997 in Runeberg Street, Helsinki, Atmospheric Environment 37, 1101-1112.
  • Ottosen, T-B, Ketzel, M, Skov, H, Hertel, O, Brandt, J & Kakosimos, KE, 2016, A parameter estimation and identifiability analysis methodology applied to a street canyon air pollution model, Environmental Modelling and Software, vol 84, pp. 165-176., 10.1016/j.envsoft.2016.06.022
  • Ottosen, T-B, Kakosimos, KE, Johansson, C, Hertel, O, Brandt, J, Skov, H, Berkowicz, R, Ellermann, T, Jensen, SS & Ketzel, M 2015, 'Analysis of the impact of inhomogeneous emissions in the Operational Street Pollution Model (OSPM)' Geoscientific Model Development, vol 8, no. 10, pp. 3231–3245., (doi-Link)
  • Palmgren, F. Hansen, A.B. Berkowicz, R. and Skov, H. (2001) Benzene emission from the actual car fleet in relation to petrol composition in Denmark. Atmospheric Environment 35, S35-S42.
  • Silver, J. D., Ketzel, M., & Brandt, J. (2013). Dynamic parameter estimation for a street canyon air quality model. Environmental Modelling & Software, 47, 235-252.(doi-Link)
  • Vardoulakis, S., Valiantis, M., Milner, M., ApSimon, H. (2007) Operational air pollution modelling in the UK—Street canyon applications and challenges, Atmospheric Environment (41), pp. 4622-4627.
  • Ziv, A., Berkowicz, R., Genikhovich, E., Palmgren, F. and Yakovleva, E. (2002) Analysis of the St. Petersburg Traffic Data using the OSPM Model, Water, Air and Soil Pollution: Focus 2(5), pp. 297-310.