Variation of 137Cs activity concentration in aerosol in Beijing

Background137Cs 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.ObjectiveTo 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.