Open road line source dispersion model

CAR-FMI (Contaminants in the Air from a Road; Härkönen 2002) is a Gaussian finite line source dispersion model i.e., a plume model for an open road network. Road is treated as a straight line of finite length.

The traffic volume of the road during one hour is assumed constant and thus the traffic emissions can be interpreted as a finite line source. The model computes an hourly time-series of the pollutant dispersion for CO, NO, NO2, NOx, O3, PM2.5, and C6H6 concentrations with input information from

  • locations of the line sources and receptor points

  • hourly average traffic volumes and speeds of the line sources

  • emission factors

  • hourly, daily, monthly, yearly time-series of the meteorology and the background concentration.

CAR-FMI uses the general analytical solution of Luhar anf Patil (1989) for the dispersion of gaseous compounds. The dispersion parameters are modelled as function of the Monin-Obukhov length, the friction velocity and the mixing height (Gryning et al., 1987). The meteorological time-series is computed by the meteorological pre-processing model (MPP-FMI; Karppinen et al., 2000). Traffic-originated turbulence is modelled with a semi-empirical treatment (Petersen, 1980). The model includes a treatment for the basic reactions of nitrogen oxides, oxygen and ozone, using a receptor-oriented discrete parcel method, and the dry deposition of the fine particles.


Gryning, S.E., Holtslag, A.A.M., Irwin, J.S., Sievertsen, B., 1987. Applied dispersion modelling based on meteorological scaling parameters. Atmospheric Environment 21, 79-89.

Härkönen, J., 2002. Regulatory dispersion modelling of traffic-originated pollution, Ph.D. thesis, Finnish Meteorological Institute Contributions 38, University Press, Helsinki, Finland, 103 pp., available at:

Karppinen, A., Joffre, S. M., Kukkonen, J., 2000. The refinement of a meteorological pre-processor for the urban environment. International Journal of Environment and Pollution 14 (1-6), 565-572.

Luhar, A.K., Patil, R.S., 1989. A general finite line source model for vehicular pollution prediction, Atmospheric Environment 25, pp. 555-562.

Petersen, W., 1980. User's guide for HIWAY2, a highway air pollution model. EPA-600/8-80-018, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, 69 p.