大气颗粒物滞留时间的测量方法研究及应用

【作者】 单健；

【导师】 肖德涛； 刘卫；

【作者基本信息】 南华大学 ， 核科学与技术、核技术及应用， 2010， 博士

【摘要】 论文系统阐述了大气颗粒物滞留时间（Residence Time of Atmospheric Aerosol,RTAA）的研究意义、研究背景、研究方法及研究现状。根据国内外的研究进展,选定²¹⁰Po/²¹⁰Pb和²¹⁰Bi/²¹⁰Pb的活度比与大气气溶胶滞留时间的关系作为主要研究内容,并把推导利用²¹⁰Po/²¹⁰Pb、²¹⁰Bi/²¹⁰Pb、²¹⁴Bi/²¹⁴Pb活度比及²¹⁰Po、²¹⁰Bi的α、β活度增长特性计算RTAA的公式作为关键研究点。同时,建立实验测量模型,设计气溶胶采样方案。用大流量粒径分级气溶胶采样器,采集上海市郊区不同粒径大气颗粒物;同时用ELPI监测该采样点大气颗粒物的粒径分布。分别用α谱仪工作站、低本底环境γ谱仪和低本底α、β探测器测量不同粒径大气颗粒物样品的²¹⁰Po、²¹⁰Pb和²¹⁰Bi活度值,对测量结果进行分析研究。最后把测量値代入推导的计算公式,分别计算不同粒径大气颗粒物的滞留时间,讨论²¹⁰Po、²¹⁰Pb和²¹⁰Bi的活度粒径分布、颗粒物滞留时间及其对环境污染的影响。在RTAA估算方法的研究中,先通过研究大气颗粒物中222Rn子体活度比与颗粒物平均寿命之间的关系,建立了基于活度比估算RTAA的方法,推导了计算公式,并在相对理想条件下的氡室进行了实验验证。得到了当氡浓度稳定为1.816 kBq/m³时,由²¹⁴Bi/²¹⁴Pb活度比计算出的RTAA为112.17分钟,与氡室的平均换气时间（104.17分钟）相当,从而证明²¹⁴Bi/²¹⁴Pb, ²¹⁰Bi/²¹⁰Pb或²¹⁰Po/²¹⁰Pb用于估算RTAA的方法及公式是正确的。在深入研究中,针对目前国际上利用²¹⁰Bi/²¹⁰Pb活度比测量和计算RTAA偏小,而利用²¹⁰Po/²¹⁰Pb得到的RTAA偏大的几个问题,提出了利用大气颗粒物中²¹⁰Po和²¹⁰Bi的活度增长关系进行RTAA测量计算的新思路,重点研究了新思路涉及的RTAA计算的新方法,通过假设和建立新的测量模型,利用巴特曼公式的原理,推导了利用²¹⁰Po和²¹⁰Bi的活度增长特性估算RTAA计算公式,然后用衰变数据对公式进行了大量的理论数据计算和证明,同时利用新公式对国外典型的实验数据进行了分析研究,最后得出改进后的方法计算RTAA更准确且简单可行的结论。为了得到实际的测量计算数据证明方法的实用性,研究中根据方法内容的具体要求,确定了实验测量研究的技术路线、实验手段和方案。利用Staplex公司的M235冲击式大流量颗粒物采样器,ELPI气溶胶测量仪,高纯锗γ谱仪、BH1216型α、β低本底测量仪和α谱仪工作站,分别采集和测量大气颗粒物的粒径分布、活度分布和RTAA的相关数据。测得采样期间上海市嘉定区采样点的样品中大气颗粒物TSP的²¹⁰Pb体积比活度为1.0629³.6324mBq/m³,平均值为1.7720 mBq/m³,其在不同粒径上的分布范围为:0.02995⁰.7740 mBq/m³。大气颗粒物中TSP的²¹⁰Pb质量比活度为6.4798¹3.4339mBq/mg,平均值为8.6511 mBq/mg,其在不同粒径上的分布范围为:0.8898¹5.4429 mBq/mg。研究发现大气颗粒物中²¹⁰Pb的体积比活度及质量比活度的最大値均落在0.49～0.95um粒径范围,此粒径范围内的²¹⁰Pb的体积比活度含量占TSP中总含量的37%,加上²¹⁰Pb在粒径小于0.49um的颗粒物中占TSP中总含量的26.2%,则有占TSP总含量63.2%的²¹⁰Pb处在粒径小于0.95um（近似PM1.0）的颗粒物中,占TSP总含量91.97%的量在PM1.5中,PM3.0中的²¹⁰Pb占TSP总含量的94.97%。实验中用α、β低本底测量仪或α谱仪工作站测量大气颗粒物中²¹⁰Bi和²¹⁰Po的活度增长特性,并把测量数据代入到新方法的计算公式中,进行实际RTAA的估算,最终得到采样期间上海市嘉定区的大气颗粒物TSP的平均RTAA为25天左右,随着粒径的减小,颗粒物的滞留时间明显增加,粒径Dp>7.2um的颗粒物MRT为16.95天,粒径Dp<0.49um的颗粒物MRT为32.33天。论文最后对整个研究实验中可能的误差进行了分析计算,给出了主要研究目标RTAA的大致误差,并对总结提出了有待进一步研究的问题。更多还原

【Abstract】 The significant meanings, backgrounds, methods and present conditions of research for Residence Time of Atmospheric Aerosol（RTAA） were systematically expounded in this paper. Relations between activities of ²¹⁰Po/²¹⁰Pb, ²¹⁰Bi/²¹⁰Pb and RATT were mainly discussed, in which the formula to calculate RTAA with activity ratios of ²¹⁰Po/²¹⁰Pb、²¹⁰Bi/²¹⁰Pb、²¹⁴Bi/²¹⁴Pb and theα,βactivity growth characteristics of ²¹⁰Po and ²¹⁰Bi was the key parts. Ambient aerosols with different diameters were collected with a high-volume sampler （Staplex, Model235, <0.49（ m） , 0.49～0.95（ m） , 0.95～1.50（ m） , 1.50～3.00（ m） , 3.00～7.20（ m）,>7.20（ m） of particle aerodynamic cutoff diameters）. Electrical low pressure impactor （ELPI） was used to investigate the size distributions of particulates. The activities of ²¹⁰Po、²¹⁰Pb and ²¹⁰Bi were detected by anαspectrometer workstation, a low-background-γ-spectrometer and low-background detectors. Put the results into the formulas and then get RATT. At last, the influences on RATT and environmental of size distributions of ²¹⁰Po、²¹⁰Pb and ²¹⁰ activities were discussed.In the study of RTAA estimation, firstly, the method of estimating RTAA based on activity quotient was established by studying the relationship between airborne particle’s 222Rn daughter activity quotient and particle’s mean life, and computing formula was deduced. Then above mentioned were verified in the radon chamber under relative optimal conditions. Through the experiment, it was found that, when the radon concentration is steadily equal to 1.816 kBq/m³, the RTAA calculated by the activity quotient of ²¹⁴Bi/²¹⁴Pb is 112.17 minutes, which is equivalent to the mean ventilation time of radon chamber（104.17 minutes）. Consequently, it was proved that it is right to estimate the method and formula of RTAA by using ²¹⁴Bi/²¹⁴Pb, ²¹⁰Bi/²¹⁰Pb or ²¹⁰Po/²¹⁰Pb.In the deep research, first of all, aiming at the international problems that the RTAA is lower measured and calculated by the activity quotient of ²¹⁴Bi/²¹⁴Pb, but higher when using the activity quotient of ²¹⁰Bi/²¹⁰Pb, new measuring thinking and method were proposed. Secondly, the mainly research about the new method of estimating RTAA was deduced by assuming and establishing new measuring model using the Betman principle. Thirdly, the formula was simulatively computed and proved by using decay data. Then typical experimental data abroad was analyzed by using the new formula. In the end, it was found that the value calculated by using the method improved is more correct and simple.To prove the practicability of the method with actual data from measurement and calculation, we selected reasonable technique routine, experimental media and experiment design for the experiment according to those specific requirements of the method.We collected atmospheric particulate matter with Staplex M235 Impact Large Flow Particulate Samplers, obtained the size distribution by ELPI aerosol measuring instrument, and then got the Specific Activity-particle size distribution of atmospheric particulate matter and relevant data of RTAA by high-purity-Geγ-spectrometer, BH1216-typeα,βlow-background measuring instrument andα-spectrometer workstation.The volume specific activity of ²¹⁰Pb in the TSP（Total Suspended Particle） collected in Shanghai JiaDing is 1.0629³.6324mBq/m³ with a mean value 1.7720 mBq/m³, and the range of different particle size is 0.02995 0.7740 mBq/m³.The mass specific activity of ²¹⁰Pb in the TSP is 6.4798¹3.4339mBq/mg with a mean value 8.6511mBq/m³, and the range of different particle size is 0.8898¹5.4429 mBq/m³.It is found that the maximum value of volume specific activity and mass specific activity of ²¹⁰Pb appeared in particle size 0.49～0.95um, with the volume specific activity accounting for 37% in TSP. The concentration of ²¹⁰Pb in particle size less than 0.49um accounts for 26.2% in TSP, so 63.2% of ²¹⁰Pb in TSP appears in particle size less than 0.95um（approximately PM1.0）, 91.97% in PM1.5 and 94.97% PM3.0. The activity property of ²¹⁰Po and ²¹⁰Bi were detected by low-backgroundα、βCounter or anα-spectrometer workstation. Put the results into the new formulas and then get RATT. The mean RATT is found to be 25 days in the TSP collected in ShangHai JiaDing and RATT increases obviously with particle size decreasing. The mean RATT is 16.95 days in particle size more than 7.2um and 32.33 days in particle size less than 0.49um.The error of the whole experiment is given in the last part of the paper.更多还原