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北京地区气溶胶中铯-137活度浓度变动规律

Variation of 137Cs activity concentration in aerosol in Beijing

    摘要
  • 摘要:
    背景  大气气溶胶中的铯-137（137Cs）是既往核武器试验和核事故的产物，137Cs释放至大气沉积在陆地和海洋环境中，造成土壤表面、水、农产品和动物副产品等污染，影响公众健康。
    目的  分析2017—2020年北京地区气溶胶中137Cs活度浓度变化规律及其与大气含尘量的相关性。
    方法  利用大流量空气气溶胶采样器采集北京2017年11月1日—2020年6月30日气溶胶样品958份。采样流量约为600 m3·h−1，每份样品采集时间约24 h，使用低本底高纯锗γ能谱仪测定气溶胶样品中137Cs活度浓度。利用采样前后气溶胶滤膜质量差计算含尘量。比较不同季节137Cs检出率和含尘量。137Cs活度浓度和含尘量的相关性分析采用Spearman秩相关检验。
    结果  2017—2020年北京地区958份气溶胶中共33份样品137Cs活度浓度在探测限以上，137Cs总体检出率为3.4%，其活度浓度的范围为1.86~45.53 μBq·m−3，中位数为4.85 μBq·m−3。137Cs检出率春季最高，秋季次之，冬季和夏季较低，检出率分别为8.4%、3.0%、1.1%和0.5%。大气含尘量范围为0.03~1.55 mg·m−3，平均值为0.18 mg·m−3，大气含尘量在春、夏、秋、冬四季中差异有统计学意义（F=45.51，P<0.05），其中春季含尘量最高（P<0.05），为0.24 mg·m−3。137Cs活度浓度与大气含尘量呈正相关（P<0.05）。
    结论  2017—2020年北京地区气溶胶中137Cs的活度浓度处于本底涨落水平范围内，其活度浓度春季最高，秋季次之，冬季和夏季较低。

     

    Abstract:
    Background 137Cs in atmospheric aerosol is the product of past nuclear weapon tests and nuclear accidents. When 137Cs is released into the atmosphere, it will deposit in dry land and marine environment, causing pollution of soil surface, water, agricultural products, and animal byproducts, and affecting public health.
    Objective To identify the variation pattern of 137Cs activity concentration in aerosol and its correlation with dust concentration in Beijing area from 2017 to 2020.
    Methods  A total of 958 aerosol samples were collected from November 1, 2017 to June 30, 2020 in Beijing with a high volume air sampler at a sampling flow rate about 600 m3·h−1 and a collection time for each sample about 24 h. The activity concentration of 137Cs in the aerosol samples was determined with a low-background high-purity germanium γ spectrometer. The dust concentration was calculated using the difference in the mass of the aerosol filter before and after sampling. The detection rate of 137Cs and dust concentration in different seasons were compared. Spearman rank correlation test was used to analyze the correlation between 137Cs activity concentration and dust concentration.
    Results  From 2017 to 2020, the 137Cs activity concentrations of 33 from 958 aerosol samples in Beijing were above the minimum detectable activityconcentration, the overall detection rate of 137Cs was 3.4%, and the activity concentration ranged from 1.86 to 45.53 μBq·m−3, with a median value of 4.85 μBq·m−3. The detection rate of 137Cs was highest in spring, followed by autumn, and lowest in winter and summer (8.4%, 3.0%, 1.1%, and 0.5%, respectively). The dust concentration ranged from 0.03 to 1.55 mg·m−3, with an average value of 0.18 mg·m−3. There was a statistically significant difference in the dust concentrations in spring, summer, autumn, and winter (F=45.51, P<0.05), and the highest value was 0.24 mg·m−3 in spring (P<0.05). The 137Cs activity concentration was positively correlated with the dust concentration (P<0.05).
    Conclusion  The 137Cs activity concentration in aerosol in Beijing from 2017 to 2020 fluctuates within the range of background level, and its activity concentration is highest in spring, followed autumn, and lowest in summer and winter.

     

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