Evaluation of the OSPM model combined with an urban background model against the data measured in 1997 in Runeberg Street, Helsinki

In 1997, a measuring campaign was conducted in a street canyon (Runeberg Street) in Helsinki. Hourly street level measurements and on-site electronic traffic counts were conducted throughout the whole of 1997; roof level measurements were conducted for approximately two months during the so-called intensive measuring campaign, from 3 March to 30 April 1997. Hourly mean concentrations of NOx, NO2, O3 and CO were measured at street and roof levels; the relevant hourly meteorological parameters were measured at roof level. We present here an evaluation of the Operational Street Pollution Model (OSPM) street canyon dispersion model against the data measured during the whole of 1997. As the roof level concentrations and meteorological measurements were not available for the whole year, we utilised computed or meteorologically pre-processed values. The use of modelled urban background concentrations and meteorological values (instead of on-site roof level measurements) did not lessen the agreement between modelled and measured average concentration values at street level. The agreement between the temporal variations of predictions and measured data was also fairly good; for instance, the corresponding index of agreement values for NOx, NO2 and CO were 0.89, 0.81 and 0.87, respectively. However, as expected, the agreement in the temporal variations was somewhat better using actual measured on-site data during the intensive measuring campaign, than when using modelled urban background concentrations and meteorological values. This study demonstrates that it is possible to utilise the street canyon dispersion model OSPM with reasonable accuracy using modelled urban background and pre-processed meteorological values as model input.