Design concept on reduction of heating and air pollution concentrations in urban areas

We determined through numerical simulations one of important causes for the urban heat island was the reduction of wind speeds by buildings. The surface temperature was determined from the balance among solar radiation from the sun, long-wave radiation from the ground and from the atmosphere, heat flux to the ground, sensible heat to the atmosphere, and latent heat for evaporation. The balance was strongly affected by wind speeds in the surface layer. The lower the wind speeds, the higher the ground temperature. Thus, the magnitude of the urban heat island decreased if the wind speeds increased. The issue was, then, how to increase the wind speeds in the surface layer in urban areas.

We proposed to raise building base away from the ground so that buildings did not block air flows in the surface layer. We performed several numerical simulations by varying the distance between the building base and the ground. If the building base was at the ground the ground temperature downstream of a building was approximately 4ºC higher than the surrounding areas where building effects were free. If the building base was raised by 10 m above the ground, the temperature increase was approximately 2ºC. When the building base was raised by 20 m or more, the temperature increase was no longer evident.

Other important benefit was reduction of air pollution concentration level in the urban areas. Automobile emissions were the main source of air pollution in urban areas. Increased wind speeds decreased pollutant concentration levels. For example, if the wind speeds were doubled, the concentration levels decreased by 50 %. Moreover the increased wind speeds increased atmospheric turbulence which in turn spread pollutants more, resulting in lower concentration levels.