The winter/summer ratio of airborne ~(210)Pb - a possible way to quantify the significance of long-range transport of natural radionuclides to the Arctic

摘要

In the environment, the main sources of naturally occurring radionuclides come from radionuclides in the uranium decay series. Activity concentrations of uranium decay series radionuclides may vary considerably from place to place depending on the geological characteristics at the location. Their releases to the atmosphere are mainly through radon (~(222)Rn), a radioactive noble gas occurring naturally as an indirect decay product of uranium in soils and rocks. Due to the abundance of uranium, radon continuously emanates from continental land masses. With radon as the main source of naturally occurring radioactivity in the environment, one would think that the Arctic should be an area of low background radiation, because a considerable area of the Arctic is covered by glaciers and permafrost, and the presence of permafrost entraps radon in the ground and serves as an effective barrier to radon emanation. However, over the past decades, ground level air monitoring data from stations in the Arctic region (UNSCEAR, 2000; AMAP, 2010; IAEA, 2012) and many special designed field studies (Lockhart, 1962; Wilkening et al., 1972; Larson et al., 1972; Polian et al., 1986; Paatero et al., 2010) have demonstrated that radon and radon progeny concentrations in the Arctic are significantly higher during the cold winter than in summer. The elevated level of naturally occurring radioactivity in the Arctic, especially during winter months, is due to radon and radon progeny produced from natural sources as well as industrial activities (such as mining, hydraulic fracturing and coal burning for power generation) outside of the Arctic, and carried to the Arctic mainly through long-range atmospheric transport (Turekian et al.. 1977; Tracy and Prantl, 1985; Samuelsson et al., 1986; IAEA, 2003; Piliposian and Appleby, 2003; AMAP, 2010; Papastefanou, 2010; Baskaran, 2011; Ram and Sarin, 2012; Charro and Pena, 2013; Persson and Holm, 2011, 2014). The long-lived radon decay products ~(210)Pb and ~(210)Po can accumulate to relatively high levels and become a health concern or a limiting factor of country food consumption (UNSCEAR, 2000; Van Oostdam et al., 2005; AMAP, 2010).