We daily bathe in urban air. So does everything else in built areas. The nature of this air overwhelmingly depends on microclimate and pollutants, which in turn are strongly determined by the built environment.

Consider the urban trees and other plants that bathe continuously outdoors. Individual trees, tree lines and woods, plus mowed grass, low spontaneous plant cover and ornamental plantings, are the prime vegetation types found repeatedly across urban areas. Individual shrubs are common, though shrubby areas tend to be uncommon despite their ecological importance (Forman, 2008).