# Radio Frequency Electromagnetic Fields Exposure Assessment in Indoor Environments: A Review
## 4 Discussion
This could be due to the concentration of people using mobile phones in public transport, usually higher than in other environments, leading to a higher probability of uplink communication and therefore higher exposures. Moreover, mobile phone use causes higher exposure for mobile scenarios (inside a train and car/bus) than for outdoor or stationary exposure due to changing environmental conditions, handovers from one base station to another, and higher required transmitted signal power from mobile phones to overcome penetration loss through (metallized) windows. This was confirmed by the maximum mean values for the uplink and downlink exposures reported in Table 3, equal to 0.96 and 0.85 V/m, respectively, and reported in literature for the transportation environments, and in particular for trains and cars. Exposure at home was considered as particularly relevant as most people spend a great amount of time at home. In most of the analyzed studies, results showed that the levels of exposure in people homes were the lowest among all the observed environments [2; 20; 70; 75], with mean values reported by the different studies in the range 0.13-0.81 V/m (see Table 3). This result could be due both to the presence of a lower number of indoor RF-EMF sources, compared to public environments such as offices, and to the fact that, at least for what concerns personal measurements, results about home exposure included nighttime observations, known to be characterized by lower levels of exposure compared to the daytime ones [20]. All the values reported in the study by [PERSON] et al. [59], related both to the broadband exposure level (equal to 0.81 V/m) and to the single contribution (e.g., the LTE downlink) were higher than all the mean/median values reported by all the other considered studies, probably due to the peculiarity of the apartment analyzed. When considering the other studies, analyzing the contribution of the different RF-EMF sources to the residential exposure, the maximum mean values was observed for the cordless phones (DECT) (equal to 0.35 V/m), whereas the WiFi was found to have lower contribution, with mean values ranging from 0.03 and 0.11 V/m. Our results about residential exposure levels are in line with those of the survey by [PERSON] et al. [4], who found mean values of exposure in the range 0.12-0.39 V/m. As to the public environments, the highest levels of exposure were found in offices, mainly due to the use of mobile phones (mean values of uplink exposure in the range 0.02-0.89 V/m) and to the use of DECT phones (mean values in the range 0.02-0.26 V/m). The outdoor base stations and the WiFi showed similar contribution to the levels of exposure, with mean values reported to be in the in the ranges 0.04-0.18 V/m and 0.03-0-19 V/m. The exposure in educational buildings, such as schools, universities, kindergartens, etc, were found to have exposure lower levels, with mean values of total exposure reported to be in the range 0.07-0.54 V/m, comparable to those observed in homes (see, e.g., [2]). In schools a very low contribution to the exposure level was due uplink or downlink mobile telecommunications, whereas the WiFi contributed to the exposure with mean levels in the range 0.01-0.29 V/m. Similar levels of exposure were observed in other public buildings, such as airports, railway stations, shopping centers, etc., with mean values of total exposure in the range 0.15-0.54 V/m (an higher level of exposure, equal to 0.99 V/m was found by [PERSON] et al. [79] in the library in Ghent: the authors explained this finding with the position of the library, about 200 m from a nearby base station, which was exactly in line-of-sight). About the contribution of different RF-EMF sources to the total level of exposure, even if slightly different patterns could be observed among the different indoor environments, results have to be interpreted with caution. As observed in the follow up study by [PERSON] et al.