Urbanheatisland Effect

The increased surface roughness created by buildings throughout a city enhances the turbulence of airflow over the city, thus improving the dispersion of the pollutants emitted. However, at the same time, the city's buildings and asphalt streets act as a heat reservoir for the radiation received during the day. This heat plus the added heat from nighttime heating during cool months creates a tempera ture and pressure differential between the city and surrounding rural area so that a local circulation inward to the city develops. This circulation concentrates the pollutants in the city.

Figure 5.6.11 shows the combined effects of the urban-heat-island effect and katabatic winds.

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