Abstract: To understand the radon concentration levels in the Chengdu metro environment, instantaneous methods and cumulative methods were used to conduct an investigation to the radon concentration levels at 31 subway stations. The results showed that the radon concentration of 279 measuring points in Chengdu metro as measured instantaneously ranged from 9.1 to 39.0 Bq/m³, with an average of (19.7±7.8) Bq/m³. The radon concentration of 124 measuring points at the subway stations as measured cumulatively twice ranged from 9.7 to 32.5 Bq/m³, with an average of (18.4±4.3) Bq/m³. The radon concentration level was significantly lower than the standard reference value. It was found that the radon concentrations inside the subway cars were lower than that at the subway stations on the corresponding line, with a positive correlation reaching 0.84 (P<0.05), and the radon concentrations at the upper security inspection points were lower than that at the lower platforms of the corresponding line, with a positive correlation reaching 0.81 (P<0.05). The radon concentrations in the open ticket halls were lower than that in the control rooms in the enclosed area on the same floor of the corresponding line. Analysis revealed that ventilation is effective in reducing the level of radon concentration in the subway. The annual effective dose of radon and its progeny in the ambient air of the Chengdu metro to the subway staff and passengers is estimated to be 0.15 mSv and 0.05 mSv respectively.

Key words: Chengdu metro, radon concentrations, cumulative measurement, instantaneous measurement, effective dose