As part of an immune response to foreign pathogens, histamine is produced by basophils and by mast cells found in nearby connective tissues. Histamine increases the permeability of the capillaries to white blood cells and some proteins, to allow them to engage pathogens in the infected tissues.
Where vegetation is sparse, temperature is hot. (Image: NASA) An urban heat island (UHI) is a metropolitan area which is significantly warmer than its surroundings. According to the EPA, many U.S. cities have air temperatures up to 10Â°F (5.6Â°C) warmer than the surrounding natural land cover.
1 The urban heat island effects can also be reduced by weather phenomona. 2  The temperature difference between the city and surrounding areas is also a function of the synoptic scale winds. 3  Strong winds reduce the temperature contrast by mixing together the city and rural air.he urban heat island is clearly evident in a statistical study of surface air temperatures (Woolum, 1964).