Numerical models are an important tool to assess the air quality in cities, as they can provide near-continouos data in time and space. In this paper, air pollution for an entire city is simulated at a high spatial resolution of 40 m. At this spatial scale, the effects of buildings on the atmosphere, like channeling or blocking of the air flow, are directly represented by diffuse obstacles in the used model CAIRDIO. For model validation, measurements from air-monitoring sites are used.