Thursday, January 8, 2009

Urban Heat Island Effect, by Brandon

Urban heat island effect occurs when cities get warmer than suburban areas. Urban heat island is happening because in the city, almost everything is black. The roofs are black and the streets are black. The black is absorbing heat, and the windows on buildings are reflecting heat from their windows.

The term, "albedo" refers to the reflectivity of color. If something has a high albedo, it means it has high reflectivity. For example, if it was a hot day you would want to wear a white shirt instead of a black one because black attracts heat and white reflects.

Three types of urban heat island effect are canopy layer, boundary layer, and surface layer. The first layer, the canopy layer, is the layer of air that is closest to the surface. It extends from the surface to the average height of a building. Above the canopy layer lies the boundary layer, which ranges from 1 km by day, and may shrink to hundreds meters or less by night. Finally, above the canopy and boundary layers lie the surface layer. This layer is measured by remote sensors mounted on satellites or aircraft.

Some buildings in Baltimore are choosing to paint their rooftops white to reflect the sun's heat and decrease the temperature of the rooftop/building. See:
This is a link to a company in Baltimore that uses paint instead of a vinyl.

Many businesses in California are using a product called "Durolast," that is a white vinyl and is applied to roof tops to cool buildings. This product does a great job of cooling a roof, but when disposed of, it can become harmful to the environment. It is also dangerous to manufacture.

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