Clearly, a better understanding of the association between the spatial distribution of urban pollutant levels with land uses, the transportation infrastructure, and the daily activities of the population is of vital importance to planners and policy makers. [...] In this paper we present a pollutant dispersion system, called CALINE+ that is capable of estimating the level of carbon monoxide (CO) pollution attributed to mobile sources at a large number of locations (receptors) of a city, when presented with an input of traffic conditions for all the links of the urban transportation network. [...] The combination of CALINE+ with IMULATE provides the opportunity to evaluate the environmental consequences of policies that affect the transport and land-use infrastructure of the city, thereby enabling to steer planning efforts towards more sustainable cities. [...] Figure 3 shows the location of the receptors in the area of study, with particularly dense areas found in the Hamilton, Burlington, and parts of Stoney Creek and Ancaster. [...] In the case of wind directions perpendicular to the motorway, the plume caused by the road traffic can be clearly identified downwind of the motorway (Kohler et al., 2005).