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.
The first local feature is the urban climate in the Chicago metropolitan area. Buildings, parking lots, roads, and industrial activities make the urban climate noticeably different than that of surrounding rural areas. For example, Chicago tends to be warmer by 2Â°F, on average, especially at night. In some cases, this difference can be higher. This particle feature of the urban climate is usually called the urban heat island effect. Urban areas also cause changes in humidity, cloudiness, wind speeds and directions.