Output power levels from mobile phones in different geographical areas;: implications for exposure assessment

Background: The power level used by the mobile phone is one of the most important factors determining the intensity of the radiofrequency exposure during a call. Mobile phone calls made in areas where base stations are densely situated ( normally urban areas) should theoretically on average use lower output power levels than mobile phone calls made in areas with larger distances between base stations ( rural areas). Aims: To analyse the distribution of power levels from mobile phones in four geographical areas with different population densities. Methods: The output power for all mobile phone calls managed by the GSM operator Telia Mobile was recorded during one week in four defined areas ( rural, small urban, suburban, and city area) in Sweden. The recording included output power for the 900 MHz and the 1800 MHz frequency band. Results: In the rural area, the highest power level was used about 50% of the time, while the lowest power was used only 3% of the time. The corresponding numbers for the city area were approximately 25% and 22%. The output power distribution in all defined urban areas was similar. Conclusion: In rural areas where base stations are sparse, the output power level used by mobile phones are on average considerably higher than in more densely populated areas. A quantitative assessment of individual exposure to radiofrequency fields is important for epidemiological studies of possible health effects for many reasons. Degree of urbanisation may be an important parameter to consider in the assessment of radiofrequency exposure from mobile phone use.