Variations of ⁷Be concentrations in the atmosphere of Guangdong Daya Bay district, China during the period 1994 to 2013

The radioactivity of ⁷Be was determined in the aerosol samples collected at Pengcheng and Dakeng in Daya Bay district of Guangdong province, south China during 1994-2013. The results showed that the ⁷Be activities ranged from 0.339 mBq·m^-3 to 10.4 mBq·m^-3 in all 119 samples at Pengcheng and from 0.335 mBq·m^-3 to 10.3 mBq·m^-3 in all 116 samples at Dakeng. The annual averages of ⁷Be (x ± s) during the twenty-year period were from (1.96 ± 1.68) mBq·m^-3 to (5.07 ± 3.18) mBq·m^-3 at Pengcheng and from (2.06 ± 1.64) mBq·m^-3 to (5.05 ± 2.01) mBq·m^-3 at Dakeng. The seasonal variations of ⁷Be activities showed the similar pattern at the two sites that the high values occurred in the autumn and winter months (October to the nest January) and the low values in the summer months. The level of ⁷Be showed negatively correlated with rainfall, which is obviously due to the leaching effect of rain, and consistent with that reported in literatures. The different number of samples collected in each year (4 ∼ 9 samples/year), not fixed sampling month (3 ∼ 16 samples/month) and variation of rainfall characteristics, resulted in greater variation of annual average of ⁷Be concentration which showed no inter annual trends. How to sum up and analysis the accumulated monitoring data for related scientific research, is an important problem needed to be solved by environmental monitoring department. (authors)