||Atmospheric processes studies and radiation dose assessment based on 7Be, 210Pb and 210Po around Xiamen Island
Men, Wu ,
Lin, Jing ,
Wang, Fenfen ,
The different sources and half-lives of radionuclides in the environment determine their differences in spatial and temporal distributions and variations, which provide the essential foundation for tracing the biogeochemical processes and indicating the velocities of environmental changes. 7Be, 210Pb and 210Po attach to the neighboring aerosol particles immediately after their production. Their half-lives are on the same order of magnitude as the time scale of those atmospheric processes. Thus, these nuclides have been widely used in the study of source items, atmospheric mixing and transport, and the residence time and rate of the removal of aerosols. The activities of 7Be, 210Pb and 210Po in the aerosol of Xiamen City from August 2014 to July 2015 were measured. The trace pair of 7Be and 210Pb was used to study the atmospheric transport processes. 7Be activities varied relatively larger, even though in the same month, especially during September 2014 to June 2015. In August-September 2014 and June-July, 2015, 7Be level was relatively low and showed a small variation range. Compared with 7Be, the variations of 210Pb and 210Po were in a small range. During November 2014 to March 2015, 210Pb and 210Po were both in a high level with larger variation. But on the contrary, they are both in a very low level in the other month. The deposition fluxes of the three nuclides had good relationships with the precipitation, which suggested that the wet precipitation is the domain controlling factor for the particle-reactive nuclides. The discussion of the source of atmospheric masses suggested that the convective mixing and removal processes were the main controlling factors for 7Be, 210Pb and 210Po in the atmosphere. The strong removal scavenging processes, such as rainfall precipitation and the conversion of land-sea breeze, which can decrease activities of 7Be, 210Pb and 210Po in a very short time. The low-level of 210Pb and 7Be may be due to the intrusion of the surface oceanic air mass. Compared with the 7Be, the trace pair of 7Be and 210Pb was more suitable for tracing O3. Based on the data of 210Pb and 210Po, the average residence time of aerosol in Xiamen city was estimated to be 21~188d with an average of 87d. Radiation dose assessment revealed that the total committed effective dose derived from 7Be, 210Pb and 210Po is 5.3μSv, which is three orders of magnitude lower than the natural background radiation.