Papastefanou C, Bondietti E A
Oak Ridge National Laboratory, Environmental Sciences Division, TN 37831.
Health Phys. 1987 Nov;53(5):461-72. doi: 10.1097/00004032-198711000-00003.
The aerodynamic size distributions of short-lived Rn daughters (reported as 214Pb and 212Pb) in ambient aerosol particles were measured using low-pressure as well as conventional low-volume and high-volume impactors. The activity distribution of 214Pb and 212Pb, measured by alpha spectroscopy, was largely associated with submicron aerosols in the accumulation mode (0.08 to 2 microns). The activity median aerodynamic diameter ranged from 0.09 to 0.37 micron (mean 0.16 micron) for 214Pb and from 0.07 to 0.25 micron (mean 0.13 micron) for 212Pb. The mean values of the geometric standard deviation (sigma g) were 2.97 and 2.86, respectively. By comparison, the median diameters of cosmogenic 7Be and ambient SO4(2-) were about 0.24 micron higher. In almost 70% of the low-pressure impactor measurements, the activity distribution of 214Pb showed a small shift to larger particle sizes relative to 212Pb. This shift probably results from alpha-recoil detachment of parent 218Po, which preferentially depletes 214Pb from smaller particles. The subsequent recondensation of 214Pb causes an enrichment of larger aerosols. Early morning and afternoon measurements indicated that similar size associations of 214Pb occur, despite humidity differences and the potential for fresh particle production in the afternoon. Health physics implications of the results are also discussed.
使用低压以及传统的低流量和高流量冲击器，测量了环境气溶胶颗粒中短寿命氡子体（以214Pb和212Pb报告）的空气动力学尺寸分布。通过α能谱法测量的214Pb和212Pb的活度分布，在很大程度上与积聚模式（0.08至2微米）中的亚微米气溶胶有关。214Pb的活度中值空气动力学直径范围为0.09至0.37微米（平均0.16微米），212Pb的活度中值空气动力学直径范围为0.07至0.25微米（平均0.13微米）。几何标准偏差（σg）的平均值分别为2.97和2.86。相比之下，宇宙成因7Be和环境SO4(2-)的中值直径大约高0.24微米。在几乎70%的低压冲击器测量中，214Pb的活度分布相对于212Pb显示出向较大粒径的小偏移。这种偏移可能是由于母体218Po的α反冲分离，它优先从小颗粒中消耗214Pb。214Pb随后的再凝结导致较大气溶胶的富集。清晨和下午的测量表明，尽管湿度不同且下午有可能产生新颗粒，但214Pb仍会出现类似的粒径关联。还讨论了结果对健康物理学的影响。
