From traffic flow simulations to pollutant concentrations in street canyons and backyards

Air pollution concentrations were computed in street canyons and backyards by means of an integrated modelling approach, consisting in the coupling of a street canyon model (OSPM) and a Gaussian model (IFDM). OSPM calculates the contribution of traffic emissions inside a particular street, whereas IFDM computes the background contributions, including the concentration levels caused by the surrounding streets, industrial stacks and domestic heating within a domain with a 20–30 km radius. Both models have been integrated into a new computer program. The coupled system was validated for NO2 and PM10 concentrations in the city of Antwerp and was applied for scenario calculations in a city quarter in Ghent, Belgium. For the scenario calculations, the traffic emissions were obtained dynamically from the traffic simulation model PARAMICS, in combination with emission measurements. For each time step and for each car, the emissions of 5 pollutants (PM, VOC, NOx, VOC and CO2) were calculated depending on the car's category, speed and acceleration. Results show that stringent European emission standards for new vehicles will lead to reductions up to 70% in 2010. Local mobility plans show only a very limited effect. The results (time series, percentiles, yearly averages) allow a quick evaluation of the urban air quality situation with respect to the EU directives on ambient air quality assessment and management.