Sesana L, Caprioli E, Marcazzan G M
Istituto di Fisica Generale Applicata, University of Milan, Via G. Celoria, 16-20133 Milan, Italy.
J Environ Radioact. 2003;65(2):147-60. doi: 10.1016/s0265-931x(02)00093-0.
The results of a survey of outdoor radon concentrations in Milan are reported. Measurements were performed hourly over a continuous four year period from January 1997 to December 2000. Radon concentration was obtained by two means: both direct measurement of radon; and measurement of its decay products. The average daily pattern of radon concentration featured a minimum in the late afternoon and a maximum in the early hours of the morning. A seasonal pattern with higher concentrations in winter than in summer (from around 15 Bq m(-3) in winter to around 5 Bq m(-3) in summer) was also observed. Similar average annual values of around 10 Bq m(-3) were obtained. The annual effective outdoor radon dose was found to be 0.12 mSv. The variation from minimum in the afternoon to maximum the following morning was found to be a good indicator of the height of the nocturnal mixing layer. The variation between maximum and minimum levels on the same day is an index of the maximum height of the mixing layer. Furthermore, our long term measurements of radon have permitted us to examine the dispersion characteristics of the atmosphere over Milan, and to establish the frequency of conditions unfavourable to the dispersion of atmospheric pollutants.
本文报告了米兰室外氡浓度的调查结果。在1997年1月至2000年12月连续四年的时间里，每小时进行一次测量。氡浓度通过两种方式获得：直接测量氡以及测量其衰变产物。氡浓度的平均日变化模式呈现为傍晚时分最低，凌晨时分最高。还观察到一种季节模式，即冬季的浓度高于夏季（从冬季的约15贝克勒尔每立方米到夏季的约5贝克勒尔每立方米）。获得的年均值类似，约为10贝克勒尔每立方米。发现室外氡的年有效剂量为0.12毫希沃特。从下午的最低值到次日早晨的最高值的变化被发现是夜间混合层高度的一个良好指标。同一天内最高值与最低值之间的变化是混合层最大高度的一个指标。此外，我们对氡的长期测量使我们能够研究米兰上空大气的扩散特性，并确定不利于大气污染物扩散的条件出现的频率。
