Urban Heat Islands :: essays research papers fc

Urban Heat IslandsFor more than 100 years, it has been know that two side by side(p) cities aregenerally warmer than the surrounding areas. This region of urban center warmth, knownas an urban heat island, can influence the concentration of channelize pollution. Theurban heat island is formed when industrial and urban areas are true andheat becomes more abundant. In agrarian areas, a large split up of the incoming solar zippo is used to e evaporationate water from vegetation and soil. In cities, whereless vegetation and exposed soil exists, the majority of the suns energy isabsorbed by urban structures and asphalt. Hence, during warm daylight hours,less evaporative change in cities allows surface temperatures to rise highthan in rural areas. Additional city heat is given off by vehicles andfactories, as well as by industrial and domestic heating and cooling units.At night, the solar energy, which is stored as vast quantities of heat in citybuildings and roads, is released s lowly into the city. The dissipation of heatenergy is slowed and make up stopped by the tall building walls that do not allowinfrared irradiation to escape as readily as do the relative level surfaces of thesurrounding countryside. The slow release of heat flows to keep citytemperatures higher than those of the unpaved faster cooling areas.On clear, still nights when the heat island is pronounced, a small thermal low-pressure area forms over the city. Sometimes a light breeze, called a countrybreeze which blows from the countryside into the city. If there are majorindustrial areas along the citys outskirts, pollutants are carried into theheart of town, where they tend to concentrate.At night, the redundant warmth of the city occasionally produces a shallow unstable grade near the surface. Pollutants emitted from low-level sources, such as homeheating units, tend to concentrate in this shallow layer, often making the air blistery to breathe.The constant outpouring of pollutants i nto the environment may actuallyinfluence the humour of a city. For an example, certain pollutants reflectsolar energy, thereby reducing the sunshine that reaches the surface. Someparticles serve as nuclei upon which water and ice form. Water vapor condensesonto these particles, forming haze that greatly reduces visibility. Moreover,the added nuclei increases the frequency of city fog.Pollutants from urban areas may even affect the weather downwind from them.Just such a fleck is described in a controversial study conducted at LaPorte, Indiana, a city located about thirty miles downwind of the industries of