Solar radiation exposure of shielded air temperature sensors and measurement error evaluation in an urban environment: a preliminary study in Florence, Italy

Particularly in summer, thermal conditions in urban areas are influenced by solar radiation and human health can be strongly affected by the higher temperature regime increased by the Urban Heat Island effect (UHI). Many studies have been carried out to estimate the temperature distribution in urban areas and some of these use or are based on data collected by meteorological instruments placed within the cities. At microscale, temperature collected by sensors can be influenced by the underlying surface characteristics and the closeness to warm surfaces. The aim of this study is to investigate how different exposure to solar radiation can affect air temperature measurement in streets and gardens. The study was carried out on two different areas in Florence during summer 2007. Shielded air temperature sensors were placed in a street of a high density built-up area and in a green area. Each area was monitored by two sensors, sited in different solar radiation exposure: one in a sunny area and the other in a shaded one. A preliminary data analysis showed a difference in every site between the air temperature values collected by the two sensors especially from the morning to the afternoon. The relationship between air temperature differences and synoptic meteorological conditions were also analyzed. In conclusion, the solar radiation exposure of a monitoring station is an important parameter that must be considered both during the instruments siting and the analysis of data collected by sensors previously placed. The result of this study shows that during particular synoptic conditions, data collected by the two sensors of the same area can be different.