Spatial distribution of air pollutants in cities

This chapter discusses the spatial distribution of air pollutants in cities in light of progress made by the scientific community in the field of flow and pollutant dispersion around buildings and within complex urban geometries. With the rate of urbanisation expected to increase in the next years, countries are forced to face challenges in addressing air pollution. Starting from the process of urbanisation and the problem of outdoor air pollution, the discussion focuses on main factors affecting flow and pollutant dispersion in cities. The dynamic of the urban atmosphere is sensitive to a large number of factors related to meteorology, building geometry and city density as well as to the presence of urban obstacles such as trees, parked cars and other barriers, buoyancy effects due to thermal exchanges at urban surfaces, traffic-induced turbulence and others. Some of them are reviewed here. The recent research towards unregulated pollutants, such as airborne ultrafine particles, which are considered to show higher health impacts compared with fine particles, is briefly addressed.