Daily Variation Of The Concentration Of Radioactive Radon In Indoor And Outdoor Environments And The Influence Factors

In recent years,the air pollution indoor and outdoor caused by the fast progress of urbanization has attracted more and more attention.Besides of chemical pollution and biological pollution,the radiation pollution also does harm to human health and ecological environment.As the only natural radioactive idle gas,radon(Rn)is an important source of radiation,so the radon pollution has becoming a topic in recent years.The indoor and outdoor radon concentrations in Xi'an were measured by RAD7 radon detector from October 2015 to September 2016.The diurnal variation of indoor and outdoor radon concentrations was examined and the effects of meteorological and ventilation conditions on radon levels were also investigated.The result are as the follows.(1)The indoor radon concentration varied between 40 and 100 Bq/m3 within one day,with high values during the night and low during the day.The concentrations showed a negative correlation with the temperature and a positive correlation with the relative humidity relation.After 3 hours in natural ventilation,indoor radon concentration could be reduced to the outdoor level.The radon concentration indoor is 4 times higher than that outdoor.Mechanical ventilation has better effectiveness compared to natural ventilation.The indoor radon concentration decreased with the increasing of ventilation rate in different airflow patterns.At the ventilation rate of 2 ACH(Air Change per Hour),radon concentration decreased to the outdoor level for all airflow patterns used in the present study.The order of descending rate is: lateral air supply and top air exit > lateral air supply and bottom air exit > lateral air supply and exit.(2)The outdoor radon concentration in Xi'an ranged from 1 to 35 Bq/m3,depending on weather conditions.The daily variation of outdoor radon concentration was still high at night and low in daytime.On haze days,there was a narrow range for diurnal variation of the radon concentration.On rainy days radon concentration had no obvious change.The order of radon levels in different weathers was: haze days> clean days > rainy days.The concentrations also showed a negative correlation with the temperature and a positive correlation with the relative humidity on clean days and haze days.The order of the correlation coefficients was: R indoor(Rn,T)>R clean days outdoor(Rn,T)> R haze days outdoor(Rn,T);R haze days outdoor(Rn,RH)>R clean days outdoor(Rn,RH)> R indoor(Rn,RH).AQI influences the radon concentration markedly.With greater haze comes a heavier risk of radon.(3)The order of radon levels was: indoors>haze days> clean days > rainy days.The indoor radon concentration in Xi'an is lower than the limit of China but higher than that all over the world.The source control,transmission control,reduce the indoor radon can be used to control the indoor radon pollution.In addition,the present results suggest that strengthening the indoor ventilation,selecting appropriate airflow pattern and keeping air clean are important measures to reduce radon concentration.