大气中氡子体行为规律及其示踪技术研究

Air particle, especially fine particles, is the main pollutent for today's air pollution issue in China. Fine particles are usually generated by the process of combustion, such as vehicle emissions in urban environments, whereas the larger particles are often associated with human activities and other mechanical means. Radon-222, a member of uranium-238 decay chain, is a natural radioactive gas with a half-life of 3.8 days omnipresent in indoor and outdoor air. Its short-lived progenies can be attached to the particles in air, and to form radioactive particles. The particles' dynamic process shortly after emissions includes condensation, evaporation, coagulation, and new particle formation. The aim of this research project is to study the mechanism of air pollution in urban local areas, to evaluate on the contribution of the main sources of air fine particles by using radon short-lived radioactive particles as a tracer. In this research project the main study contents include: study on the activity of atmospheric radon progeny, both short-lived and long-lived radon progeny is considered; mathematical modeling to describe the activity of radon progeny through theoretical study; to simulate the variation of atmospheric radon progeny concentration by adopting meteorological factors. Experimental measurements on atmospheric radon concentration, radon progeny concentration, total bate activity of air aerosols, air aerosol particle size distribution and concentration in both number concentration and PM2.5 will be carried out to get key parameters for modeling study and simulation.

本项目是上一结题项目"室内环境中气溶胶对氡子体暴露剂量影响研究"的延伸与拓展。研究对象从室内环境延伸到室外低层大气环境，关注焦点从氡子体辐射暴露剂量评价转移至大气颗粒物对室外氡子体行为规律影响。 本项目研究目的是在当前以细颗粒物为大气污染成分的环境背景下，以放射性气溶胶氡子体(包括短寿命子体和长寿命子体)为观测指针，粗估大气细颗粒污染物的源项贡献，对其运移过程进行描述。 本项目拟解决低层大气中氡子体行为规律及其示踪技术应用相关的诸多问题。从气溶胶生成基本物理机制入手，结合理论研究和现场实验测量，研究低层大气中氡子体的分布及其行为运移规律，探讨降雨对氡子体洗刷效应，气团运移对其的稀释效应。基于此建立大气氡子体模型，结合气象数据对近地表大气中氡子体浓度变化进行仿真模拟计算。希冀研究开发短寿命氡子体示踪城市局域环境大气污染物技术，解释近地表层大气污染物浓度变化的机理，并对污染物源项进行评价。

放射性惰性气体氡（Rn-222）是以铀-238 为起始核素的天然衰变链上的唯一的气体核素，半衰期为 3.825 天，在大气中，衰变产生一系列短寿命的氡子体和长寿命氡子体。氡暴露导致的辐射危害一直是辐射防护领域的热点研究问题。相对于系统的室内环境氡及子体研究，室外大气中氡及子体由于其浓度相对较低，测量困难，长期以来大气氡及其子体行为规律研究一直开展有限。灵敏有效的连续测量技术及装置的研发建立是开展大气中氡及其子体行为规律研究必不可少的技术基础和前提。本项目研究目的是在当前以细颗粒物为大气污染成分的环境背景下，以放射性气溶胶氡子体为观测指针，粗估大气细颗粒污染物的源项贡献，对其运移过程进行描述。本项目的主要研究内容包括：低层大气中氡及氡子体连续在线测量装置的研发；大气中氡及子体行为规律及相关影响因素分析研究；连续测量城市局域环境大气中氡及子体和大气污染物PM2.5浓度，分析不同大气稳定度下观测指标的相互关系。本项目成果：研发建立了基于Si-PIN探测器的大气氡浓度测量技术，测量灵敏度21cph/Bqm3; 探测下限0.18Bq/m3；研发了步进走纸式氡子体浓度连续监测仪，可以同时给出各个子体浓度和EEC浓度；60分钟测量周期时EEC探测下限为0.07Bq/m3，实现了自动连续对大气中短寿命氡子体浓度进行常年连续；主要结论：氡气和氡子体浓度有规律近似的显著日变化，PM2.5浓度则没有；室外环境中平衡因子，PM2.5浓度较低时，氡子体浓度依然相对较高，二者相关性较弱；降雨洗刷导致的地表氡子体Bi-214浓度升高是γ剂量率波动的最大贡献者。