Spatiotemporal characteristics and mechanisms of 7Be and 210Pb in the atmosphere

[Background]: 7Be and 210Pb are the main radionuclides for monitoring the quality of the radiation environment of atmospheric aerosols, and the internal irradiation caused by their adsorption into aerosols and entry into the human body will be harmful to the human body, so it is of great significance to explore the characteristics and mechanisms of their spatial and temporal distribution and dose contribution. [Purpose]: The aim of this study is to investigate the differences in the spatial and temporal distributions of atmospheric 7Be and 210Pb and the mechanisms of these differences.  [Methods]: In this paper, 75 aerosol samples were collected from Nanning City, Guangxi, from January 2015 to December 2017 and from January 2019 to May 2022 using an ultra-high-flow air aerosol sampler, and the activity concentrations of 7Be and 210Pb in the aerosol were measured and analyzed using a high-purity germanium γ-spectrometer. We systematically collected the activity concentration data of 7Be and 210Pb in 17 areas of the country, as well as PM2.5, PM10 and O3 air concentration data from January 2014 to November 2023 in Nanning. The HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory Model) model was used for the atmospheric traceability model. [Results]: The activity concentrations of 7Be in 41 aerosol samples from January 2019 to May 2022 ranges from 0.27 to 11.95 mBq/m3, with a mean value of 3.68±0.51 mBq/m3; the activity concentrations of 210Pb in 60 aerosol samples from January 2015 to December 2017 and from January 2019 to February 2021 ranges from 0.23 to 4.33 mBq/m3, with a mean value of 1.51±0.13 mBq/m3. Combining the 7Be and 210Pb activity concentration data in 17 areas of China, the seasonal distribution of 7Be and 210Pb activity concentrations in the atmosphere of China is characterized by an overall high in winter and spring, and a low in summer and autumn, but 7Be reaches its maximum value in spring while 210Pb in winter. The correlation analysis shows that 7Be has a significant positive correlation with PM2.5, PM10, O3, and has the best correlation with PM10. 210Pb has a significant positive correlation with PM2.5 and PM10 and has the best correlation with PM2.5, while it is not correlated with O3. The traceability analysis of air masses in Nanning City of the 2021 shows that the summer air masses mainly come from the oceanic air masses in the south with lower particle concentration, and the winter air masses mainly come from the continental air masses in the north with higher particle concentration. Combining the 7Be and 210Pb activity concentration data in 17 areas of China, there are effects in the spatial distribution of 7Be and 210Pb activity concentrations. The latitudinal effects: the mean 210Pb activity concentration in the area north of about 40°N (3.20±0.24 mBq/m3) is about 2.2 times higher than that in the area south of about 40°N (1.48±0.06 mBq/m3); the mean value of 7Be activity concentration in the area north of about 35°N (7.44±0.26 mBq/m3) is about 1.9 times of that in the area south of about 35°N (3.92±0.19 mBq/m3). The altitudinal effect: the 7Be activity concentration is greater at high altitude than at low altitude. Based on the average of winter-spring and summer-autumn activity concentrations of 7Be and 210Pb in 17 regions of the country, it can be estimated that the radiation dose due to 7Be and 210Pb in winter-spring (42.08 μSv/a) is about 1.4 times higher than that in summer-autumn (31.00 μSv/a). Integration of monitoring data on activity concentrations of 7Be and 210Pb in 17 regions of the country reveals that the annual effective dose due to 7Be and 210Pb in the area north of 40°N (65.48 μSv/a) is about 2.0 times higher than that in the area south of 35°N (32.75 μSv/a). The mean annual pending effective doses due to 7Be and 210Pb are 2.47×10-3 μSv/a and 33.57 μSv/a, respectively.  [Conclusions]: 7Be and 210Pb are adsorbed on the particulate matter and transported in the atmosphere, and the PM2.5 and PM10 concentrations are low in summer and autumn while high in winter and spring due to the monsoon regulation, so the 7Be and 210Pb show the seasonal distribution characteristics of low in summer and autumn and high in winter and spring. The highest 7Be activity concentration in spring is related to the "spring leakage", while the highest 210Pb activity concentration in winter is mainly influenced by the Eurasian land-based air masses in the north. The latitudinal effect of 210Pb is probably related to the large amount of particulate matter brought by the northwest land-source winds in winter and the combustion process in winter heating system. The latitudinal effect of 7Be may be attributed to the “spring leakage” of 7Be that occurs in mid-latitudes in the spring. The altitudinal effect of 7Be is controlled by the top-down transport of 7Be from the stratosphere to the troposphere.

[背景]：7Be和210Pb是监测大气气溶胶辐射环境质量的主要放射性核素，其吸附于气溶胶并进入人体引发的内照射（internal irradiation）会对人体造成危害，因此探究二者时空分布特征、机制及剂量贡献具有重要意义。
[目的]：本研究旨在揭示大气中7Be和210Pb时空分布的差异及其机制。
[方法]：本文采用超高流量大气气溶胶采样器，于2015年1月至2017年12月、2019年1月至2022年5月在广西南宁市采集75份气溶胶样本，并利用高纯度锗γ谱仪测定分析样本中7Be和210Pb的活度浓度。系统收集全国17个区域的7Be和210Pb活度浓度数据，以及南宁市2014年1月至2023年11月的PM2.5、PM10和O3浓度数据；采用HYSPLIT（混合单粒子拉格朗日积分轨迹模型，Hybrid Single-Particle Lagrangian Integrated Trajectory Model）进行大气溯源分析。
[结果]：2019年1月至2022年5月41份样本中7Be活度浓度范围为0.27至11.95 mBq/m³，平均值为3.68±0.51 mBq/m³；2015年1月至2017年12月及2019年1月至2021年2月60份样本中210Pb活度浓度范围为0.23至4.33 mBq/m³，平均值为1.51±0.13 mBq/m³。结合全国17个区域的7Be和210Pb活度浓度数据，我国大气中二者活度浓度的季节分布总体呈现冬春季高、夏秋季低的特征，但7Be在春季达到峰值，而210Pb在冬季达到峰值。相关性分析显示，7Be与PM2.5、PM10、O3均呈显著正相关，且与PM10相关性最优；210Pb与PM2.5、PM10呈显著正相关，与PM2.5相关性最优，与O3无相关性。2021年南宁市气团溯源分析表明，夏季气团主要来自南方海洋气团（颗粒物浓度较低），冬季气团主要来自北方大陆气团（颗粒物浓度较高）。结合全国17个区域数据，7Be和210Pb活度浓度存在空间分布效应：纬度效应方面，北纬约40°以北区域210Pb平均活度浓度（3.20±0.24 mBq/m³）约为北纬40°以南区域（1.48±0.06 mBq/m³）的2.2倍；北纬约35°以北区域7Be平均活度浓度（7.44±0.26 mBq/m³）约为北纬35°以南区域（3.92±0.19 mBq/m³）的1.9倍。海拔效应方面，7Be活度浓度随海拔升高而增大。基于全国17个区域7Be和210Pb冬春季与夏秋季活度浓度平均值估算，冬春季二者所致辐射剂量（42.08 μSv/a）约为夏秋季（31.00 μSv/a）的1.4倍；整合全国17个区域数据发现，北纬40°以北区域7Be和210Pb年有效剂量（65.48 μSv/a）约为北纬35°以南区域（32.75 μSv/a）的2.0倍。7Be和210Pb的年均待积有效剂量分别为2.47×10⁻³ μSv/a和33.57 μSv/a。
[结论]：7Be和210Pb吸附于颗粒物并在大气中传输，受季风调控影响，PM2.5和PM10浓度呈现夏秋季低、冬春季高的特征，因此二者季节分布表现为夏秋季低、冬春季高。7Be春季活度浓度峰值与“春季泄漏”（spring leakage）相关，而210Pb冬季峰值主要受北方欧亚大陆气团影响。210Pb的纬度效应可能与冬季西北陆源风携带的大量颗粒物及冬季供暖燃烧过程有关；7Be的纬度效应或归因于春季中纬度地区发生的7Be“春季泄漏”；7Be的海拔效应由平流层向对流层自上而下的传输过程控制。