Finally, the number of HDVs in the fleet plays a significant role in
the concentrations observed at street level. To study the sensitivity
of local air quality on the percentage of HDVs assumed, air pollution
in the narrow canyon configuration was estimated for seven cities
(Athens, Berlin, Milan, Rome, Stuttgart and Thessaloniki) assuming
instead of 7%, a HDV fraction of 15%. As can be seen in Figs. 7 and 8
this assumption leads to an increased estimate of both NO2 and
PM10 concentrations, with the increase depending on the specific
composition of the HDV fleet in each city. In countries such as
Greece (Athens and Thessaloniki) where old technology and more
polluting vehicles are still used, the increase is larger than in