Urban Heat Islands :: essays research papers fc

urban Heat IslandsFor more than 100 years, it has been known that two adjacent cities argenerally warmer than the ring areas. This region of city oestrus, knownas an urban rouse island, can influence the concentration of air pollution. Theurban heat island is formed when industrial and urban areas are developed andheat becomes more abundant. In rural areas, a large part of the entering solarenergy is used to evaporate water from vegetation and soil. In cities, whereless vegetation and exposed soil exists, the majority of the suns energy is enwrapped by urban structures and asphalt. Hence, during warm day swingy hours,less evaporative temperature reduction in cities allows surface temperatures to rise higherthan in rural areas. excess city heat is given off by vehicles andfactories, as healthy 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 slow into the city. The dissipation of heatenergy is slowed and even stopped by the high building walls that do not allowinfrared radiation to dodging as readily as do the relative level surfaces of thesurrounding countryside. The slow release of heat tends to keep citytemperatures higher than those of the caliche-topped faster cooling areas.On clear, still nights when the heat island is pronounced, a wee 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 distill.At night, the extra warmth of the city occasionally produces a shallow unstablelayer practiced the surface. Pollutants emitted from low-level sources, such as homeheating units, tend to concentrate in this shallow layer, often making the airunhealthy to breathe.The everlasting outpouring of pollutants into the environm ent may actuallyinfluence the climate of a city. For an example, certain pollutants reflectsolar energy, thereby reducing the sunlight that reaches the surface. Someparticles serve as nuclei upon which water and ice form. Water vapor condensesonto these particles, forming fog that greatly reduces visibility. Moreover,the added nuclei increases the frequency of city fog.Pollutants from urban areas may even propel the weather downwind from them.Just such a situation is exposit in a controversial study conducted at LaPorte, Indiana, a city located about thirty miles downwind of the industries of