Long description of model 'OSPM'

Table of Contents:

For help concerning the various sections see this page


Basic information [top]

Model name
OSPM

Full model name
Operational Street Pollution Model (OSPM)

Model version and status
The model is available as Windows version - WinOSPM

Latest date of revision
30-03-2007

Institutions
National Environmental Research Institute, Department of Atmospheric Environment

Contact person
Matthias Ketzel

Contact address
National Environmental Research Institute
Department of Atmospheric Environment
Aarhus University
P.O. Box 358, Frederiksborgvej 399,
DK-4000 Roskilde, Denmark

Phone number
+45 46 301171

Fax number
+45 46 301214

E-mail address
mke@dmu.dk

URL
http://ospm.dmu.dk

Technical support
Provided by contact person

Level of knowledge needed to operate model
Intermediate

Intended field of application [top]

Simulation of air pollution from traffic in urban streets

Model type and dimension [top]

A combined plume and box model

Model description summary [top]

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 formulas for concentration of pollutants in the street are derived applying the constrain that a continuous transition must be obtained between the different flow regimes. This concerns especially the transition from the recirculating regime at higher wind speeds to the non-recirculating regime at lower wind speeds. The same applies for the case of vanishing vortex when the wind direction changes from perpendicular to parallel with the street. Expressions used for the direct contribution and the recirculation contribution are constructed to fulfill these requirements.
The direct contribution is calculated using a simple plume model. It is assumed that both the traffic 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 and the sources are treated as infinite line sources. 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 contribution from the recirculation part is calculated assuming 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.
The turbulence within the canyon is calculated taking into account the traffic created turbulence.
The NO2 concentrations are calculated taking into account NO-NO2-O3 chemistry and the residence time of pollutants in the street.

Model limitations/approximations [top]

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.

Resolution [top]

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

Horizontal resolution
Concept not applicable.

Vertical resolution
Concept not applicable. The model calculates concentrations at any specified hight above the street level.

Schemes [top]

Advection & Convection
Not applicable for this kind of empirical plume/box model.

Turbulence
Not applicable for this kind of empirical plume/box model.

Deposition
no deposition considered

Chemistry
Only NO-O3-NO2 chemistry.

Solution technique [top]

Analytical solutions for simple integration of plume / box formulations.

Input [top]

Availability and Validation of Input data

OSPM requires input data on wind speed and wind direction at roof level. No further pre-processing of meteorological data is required. Urban background concentrations are also required as input for the model. The largest uncertainty in input data is however connected with the traffic emission data.
Reference:
Berkowicz et al., (2006) Traffic pollution modelling and emission data, Environmental Modelling & Software 21, 454-460

Emissions
The emissions are calculated from the traffic volume and the vehicle specific emission factors. Speed dependent expressions for vehicle specific emission factors are supplied with the model. The user can modify these expressions or supply own expressions.

Meteorology
The required meteorological data are wind speed and wind direction above roof level. Temperature and global radiation are used for calculation of NO2.

Topography
Information is required about the street configuration and the heights of the buildings along the street.

Initial conditions
The model does not incorporate initial conditions.

Boundary conditions
Background pollution levels are required as input to the model. For calculation of primarily pollutants (such as NOx, CO and benzene) background concentrations are required. For calculation of NO2, background concentrations of O3 are required beside background concentrations of NO2 and NOx. For special applications, when the background data are not available, statistical methods are developed for estimation of background concentrations. These, however, are only applicable for long-term calculations in connection with e.g. human exposure studies.

Data assimilation options
The model does not incorporate data assimilation.

Other input requirements
Traffic flow, either as hourly values or as average daily variation.
Information on the street geometry.
Urban background concentrations of calculated pollutants.
Hourly meteorological data.

Output quantities [top]

Hourly concentrations of all calculated pollutants or/and statistical parameters as average values and percentiles.

User interface availability [top]

Windows user interface, which provides the user with the possibility to specify all the input data, concentration units and input- output files. The input- and output files can either be text files, Excel or Access files. Data formats and list of input- or output variables can be specified by the user. Special Windows modules are provided for editing or visualisation of traffic and emission data.

User community [top]

Air Quality management and research.
Exposure and health effect studies.
Is part of GIS bases the exposure modelling system AirGIS ( http://www.dmu.dk/International/Air/Models/AIRGIS/ )
Is part of the pollution forecast system THOR ( http://thor.dmu.dk/ )

Previous applications [top]

1.
Application type
Urban
Application description
Human exposure to traffic pollution
OSPM is extensively used for evaluation of traffic pollution in connection with studies on human exposure in urban areas. Application of OSPM in this context is normally a part of a larger epidemiological study of traffic related pollution. The model is used for estimation of pollution levels at the specified locations, usually residential addresses of the subject persons. The model calculations are performed for the exposure period of interest, which can vary from few months to several years. The data are subsequently used for statistical evaluation of association between air pollution and different effects on humans. A GIS-based system (AirGis) is especially developed to make it possible to generate the large amount of data required as model input and subsequent linkage of air quality and population data.
AirGIS web page: http://AirGIS.dmu.dk/
A unique data set of NO2 measurements was collected in connection with a large epidemiological study on traffic pollution and children cancer. These measurements were conducted in the years 1994-95 using passive samplers placed at 204 street locations in Copenhagen as well as in some smaller towns and the adjacent rural areas. At each location NO2 concentrations were measured during a consecutive period of 6 months with a sampling period of one month. The sampling locations covered street-canyons as well as streets with scattered buildings or practically open locations. The traffic at the streets varied from a few vehicles per day and up to more than 50,000 vehicles per day. Performance of OSPM was evaluated using this dataset focusing on model`s ability to reproduce the observed spatial and temporal variability of NO2 levels. The study covered also evaluation of different methods for estimation of the necessary input data, such as traffic, street geometry and background pollution. The results have shown that the model can satisfactory predict the variability of pollution levels in urban environment but the agreement was less perfect in the rural areas were the impact of the local traffic emissions was also less pronounced. Uncertainty in traffic data and street geometry has large influence on the model performance.
Relevant references:
-Hertel, O., Jensen, S.S., Berkowicz, R., Brandt, J. & Christensen, J. (2002): Modelling Concentrations of and Human Exposure to Air Pollution in Danish Cities. In: Midgley, P. & Reuther, M. (eds.): Transport and Chemical Transformation in the Troposphere. Proceedings of EUROTRAC-2 Symposium 2002. Margraf Verlag. 5 pp.
-Jensen, S.S., Berkowicz, R., Hansen, H.S. & Hertel, O. (2001): A Danish Decision-Support GIS Tool for Management of Urban Air Quality and Human Exposures. - Transportation Research Part D 6(4): 229-241.
-Raaschou-Nielsen, O., Hertel, O., Vignati, E., Berkowicz, R., Jensen, S.S., Larsen, V.B., Lohse, C. & Olsen, J.H. (2000): An Air Pollution Model for Use in Epidemiological Studies: Evaluation with Measured Levels of Nitrogen Dioxide and Benzene. - Journal of Exposure Analysis and Environmental Epidemiology 10: 4-14.
-Jensen, S.S. (1999): A Decision-Support GIS Tool for Management of Urban Air Quality and Human Exposures. In: Sturm, P.J. (ed.): 8th International Symposium Transport and Air Pollution including COST 319 Final Conference. Graz, Austria, 31 May - 2 June 1999. Technical University Graz. Institute for Internal Combustion Engines and Thermodynamics. - Report of the Institute for Internal Combustion Engines and Thermodynamics 76: 389-401.
- Berkowicz, R., Ketzel, M., Jensen, S.S., Hvidberg, M. & Raaschou-Nielsen, O. (2007): Evaluation and application of OSPM for traffic pollution assessment for a large number of street locations. Journal of Environmental Modelling and Software (In press).
2.
Application type
Urban
Application description
Impact Assessment of Abatement Measures for Compliance with NO2 Air Quality Limit Values For 2010 in Copenhagen.
Elevated air pollution levels of nitrogen dioxide (NO2) have been measured at the central air quality monitoring site in Copenhagen. Road traffic is the main cause of the NO2 problem, and observed levels have been more or less constant in recent years. Measurements from 2002 and 2003 show that the limit level for annual mean plus margin of tolerance was violated. As a consequence, EU regulation requires that the Danish Environmental Protection Agency (EPA) in close co-operation with local authorities have to prepare an action plan to insure that limit values are met in 2010. Accordingly, the Environmental Protection Agency of the Municipality of Copenhagen in co-operation with the Danish EPA has requested an assessment of abatement measures to ensure that NO2 limit values are met in 2010, accompanied by an assessment of associated public costs. Model calculations with OSPM were performed for 138 selected road links assuming several different abatement measures and the expected levels of NO2 were analysed. The results of the study indicated that the considered traffic restriction scenarios, such as toll ring and road pricing, will only have a modest effect on the ambient NO2 levels. Only significant reduction of traffic emissions, i.e. `the cleaner technology scenario` is expected to lead to sufficient reduction of NO2 pollution.
Relevant references:
Jensen, S.S., Ketzel, M., Berkowicz, R., Hvidberg, M., H�j, J. & Krawack, S. (2005): Impact Assessment of Abatement Measures for Compliance with Air Quality Limit Values For 2010 in Copenhagen. In: Sturm, P. & Minarik, S. (Eds.): 14th International Symposium Transport and Air Pollution, 1-3 June 2005, Graz, Austria. Proceedings Volume I. Verlag der Technischen Universitat Graz. - VKM-THD Mitteilungen 85-I: Pp. 51-56.

Documentation status [top]

Level 2: Scientific description of the physical principles of the model is provided in,
-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.
A short description is available on http://ospm.dmu.dk
The Windows version of the model, WinOSPM is supplied with a Users Guide (in English), which provides details on application of the software. The User`s Guide is however not yet updated with the newest options and features of the software.

Validation and evaluation [top]


Level 1: The model has extensively been tested against measurements at several street locations. Special attempt was on verification of the reproducibility of the dependency of concentrations on the meteorological conditions.
More evaluation is required in order to elucidate the variability of the model performance with the type of street location. The physical principles of the model result in that the model is best suitable for regular street-canyons, but a reasonable model performance was also obtained in the case of more complex street geometries. Examples of comparison of model results with measurements is provided in several cited here publications and reports. More detailed data on model performance for particular street locations is given e.g. in:
-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.
- 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
- 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.

Model intercomparison
ETC-ACC Street Emission Ceiling (SEC) exercise
http://air-climate.eionet.europa.eu/docs/ETCACC_TechnPaper2003_11_SEC_Phase1Rep.pdf
http://air-climate.eionet.europa.eu/docs/ETCACC_TechnPaper_2004_5_SEC_Phase2Rep.pdf
OSPM was among the several other models used for comparison of model predictions with measurements from 3 different street locations: Hornsgatan in Stockholm, Frankfurter Allee in Berlin and Marylebone Rd. in London. Model results were in general in good agreement with measurements for NOX, NO2 and CO. However model predictions for PM (this concerns all the tested models) were less satisfactory. The main reason for this was the lack of ability to model the dominating part of PM attributed to road-wear and other non-exhaust sources.. Slightly different versions of OSPM were applied by different users (NERI Denmark, ESMG Spain and LHTEE Greece). The results were, however, comparable. Larger differences could have been attributed to different assumptions on traffic emission factors and selection of the meteorological data. Due to a limited evaluation dataset, statistical measures of model performance cannot be applied.
The primary objective of the Street Emission Ceilings (SEC) project was to develop a method for determining what local emission reductions in streets are needed to reach certain air quality thresholds, e.g. limit values. In particular, SEC has two purposes namely (a) Use by local authorities and (b) Use in Integrated Assessment Modelling (IAM) for the Clean Air For Europe (CAFE) programme. Subsequently, OSPM in combination with the OFIS model was applied for evaluation of future air pollution levels at traffic hotspot areas in 20 European cities (http://air-climate.eionet.europa.eu/reports/EEA_Techn_Rep_1_2006).

Frequently asked questions [top]

  • Q: Can the model be applied for shorter time averages than one hour?
    A: The highly intermittent character of the turbulent flow in street-canyons prevents applications for much shorter times than one hour
  • Q: Can the model be applied for calculation of particular pollution?
    A: A size fractioned source term for particulates must be determined separately. A module for calculation of transformations of particles in the street air is under development.

Portability and computer requirements [top]

Portability
The model can run on any Win32 PC.

CPU time
One year calculation on a Pentium 600 Mhz PC requires less than 20 s CPU-time

Availability [top]

An evaluation version (100 days period) can be downloaded from http://ospm.dmu.dk
An updated version (WinOSPM 5.2) is under preparation.

References about model development (up to 5) [top]

  • Berkowicz, R.., Hertel, O., Sorensen, N.N. and Michelsen, J.A. (1997) Modelling air pollution from traffic in urban areas, Proceedings, IMA Conference on Flow and Dispersion Through Groups of Obstacles, University of Cambridge, 28-30 March 1994.
  • 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.
  • Hertel, O. and Berkowicz, R. (1989) Modelling pollution from traffic in a street canyon. Evaluation of data and model development, DMU Luft A-129, 77p.
  • Hertel, O. and Berkowicz, R. (1989) Modelling NO2 concentrations in a street canyon, DMU Luft A-131, 31p.

Other references [top]

  • Kumar, P., Garmory, A., Ketzel, M., Berkowicz, R. and Britter, R. (2009): Comparative study of measured and modelled number concentrations of nanoparticles in an urban street canyon. Atmospheric Environment 43, 949-958.
  • Berkowicz, R., Ketzel, M., Jensen, S.S., Hvidberg, M. & Raaschou-Nielsen, O. (2008): Evaluation and application of OSPM for traffic pollution assessment for a large number of street locations. Journal of Environmental Modelling and Software 23, 296-303.
  • Berkowicz,.R., Palmgren F., Hertel, O. and Vignati, E. (1996) Using measurements of air pollution in streets for evaluation of urban air quality - meteorological analysis and model calculations. The Science of Total Environment 189/190, 256-265.
  • Berkowicz, R., Hertel, O., Larsen, S.E., Srensen, N.N. and Nielsen, M. (1997) Modelling traffic pollution in streets (available on request from NERI).
  • 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 Nantes99 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.
  • 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., Mller, 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
  • 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.
  • 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.

 

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