Investigating and Measuring Radon Gas Concentration in Tehran and Alborz Metro Stations

Abstract

Humans are regularly exposed to various types of radioactive radiation and, of course, to Radon-222 over the course of their lives. According to the report of the United Nations scientific committee on the effects of atomic radiation in 2000, the average human is estimated to be exposed to about 4.2 mSv of radioactive radiation each year, 52% of which is caused by inhalation of radon gas. The radon gas is one of the most important elements that is emitted from the decay of natural uranium and radium in the earth. Therefore, the concentration of this gas can be higher in enclosed spaces, especially underground locations, and it is important to measure the amount of radon gas radiation in these underground stations. In this research, a domestically manufactured environmental meter for radon gas was used to measure the concentration of this gas in different Tehran metro stations. In general, all 42 subway stations of Tehran and Karaj cities were measured at continuous time intervals during the spring season. On average, trace amounts of radon gas were observed in all the stations, but high concentrations of radon gas were measured at some stations, such as Tajrish and Ghaem stations in the northern Tehran-Karaj plain due to underground water resources, fault type and distinct geological structures. According to the US Environmental Protection Agency (EPA) standard, the maximum permissible amount of radon gas concentration in the air is 148 Bq/m3, while the average amount was 156 Bq/m3 at Tajrish station. This amount is above the permissible limit and can therefore be considered hazardous to health. Geologically, the Meydan-e-Azadi (Azadi square) station on line 4 located in the center of Tehran also revealed a near high radon concentration due to bedrock that it mainly has been consisted of calcite. Consequently, measures for better ventilation and easier air movement are required in such stations.