urban heat island

The name given to a well-studied effect in urban climatology, which describes the warming to which the air covering a large city is subjected. The asphalt and concrete of the streets, the concrete and refractory materials buildings are made of, radiate a significant amount of infrared energy into the urban environment, warming the air. The result is the formation of a kind of gaseous dome, whose temperature is higher than that of the air in the periphery. Gases from vehicle combustion and chimneys also contribute to the heat island, whose extent and magnitude vary depending on different factors, such as the meteorological situation, the time of year (a more or less cold environment), and the characteristics of the urban layout. While during the day temperature differences between the city center and its surroundings rarely exceed 3°C, at night the heat island is much more pronounced, and differences of up to 10°C can occur in some cases. The presence of pollutants is another characteristic of the heat island, due to the emission of harmful gases and particles, mainly from traffic and heating. Under winter situations of marked atmospheric stability, with a thermal inversion present above the city, poor ventilation contributes to the progressive increase in the concentration of those pollutants, which is harmful to citizens' health. The study of urban heat islands is one of the main fields of research in urban climatology.