Seasonal variation of Beryllium-7 relative to Caesium-137 in surface air at tropical and sub-tropical latitudes

Assessment of temporal variations of natural radionuclides Beryllium-7 and Lead-212 in surface air in Tanay, Philippines

Detection of radionuclides in surface air allows researchers to gain further insight on the behavior of radionuclides that may affect human radiation exposure especially in the event of a nuclear emergency. In this study, activity concentrations of naturally-occurring radionuclides Beryllium-7 (⁷Be) and Lead-212 (²¹²Pb) in surface air and meteorological data collected in Tanay, Philippines from January 2012 to December 2017 were evaluated to determine the impact of atmospheric conditions and processes to airborne radioactivity. Surface air concentrations of ⁷Be and ²¹²Pb were found to range from 0.00779 ± 0.00188 to 11.2 ± 0.116 mBq/m³ and from 1.371 ± 0.036 to 106.6 ± 1.075 mBq/m³, respectively. ⁷Be and ²¹²Pb show distinct annual trends, suggesting that atmospheric conditions affect both radionuclides differently and independently. ⁷Be shows two peak concentrations annually, with the first peak occurring between January to April and the second lower peak occurring between October and November. ²¹²Pb, on the other hand, shows annual peak concentrations occurring between April and June. Ambient temperature showed strong positive correlation with ²¹²Pb concentration in surface air and a weak negative correlation with ⁷Be; relative humidity and precipitation showed varying degrees of negative correlation with radionuclide concentrations in surface air. Source locations for the unusually high ²¹²Pb activity concentrations detected on 11-13 May 2013 and 19-31 May 2015 determined using WEB-GRAPE and HYSPLIT atmospheric transport models are presented as a case study. The data and findings of this study shall serve as basis for further studies on local and regional atmospheric transport and radiological impact assessment for the implementation of an effective nuclear and radiological emergency preparedness and response system in the country.

A study of temporal variations of 7Be and 210Pb concentrations and their correlations with rainfall and other parameters in the South West Coast of India

As a part of establishing a regional database on natural radioactivity, the atmospheric concentrations of ²¹⁰Pb and ⁷Be were measured over a three and half year period (2014-2017) in Mangalore and Kaiga in the South West Coast of India. A total of 99 air samples, collected in the different months of the year, were analysed in this study. The mean activity concentrations of ⁷Be and ²¹⁰Pb were found to be 5.5 ± 3.1 mBq m^-3 and 1.1 ± 0.73 mBq m^-3, respectively. Both the radionuclides exhibited strong seasonal variations, with maximum concentration of ⁷Be occurring in the summer and that of ²¹⁰Pb in the winter season. The concentration of both the radionuclides was minimum in the rainy season. Higher ²¹⁰Pb concentration during winter was attributed to the ingression of continental air masses due to the wind regime from the North East. The sunspot number index of the solar activity also plays an important role in the increase and decrease of ⁷Be concentration in the air. A clear trend of increased and lowered concentration of ⁷Be with lower and higher solar activity (low and high sunspot number), respectively, in accordance with the 11-year solar cycle, was observed in this study. The temporal variation of PM₁₀ concentration was also studied and it showed maximum value in the winter and minimum in the rainy season with an average of 56.9 μg m^-3. Statistically significant positive correlation was observed between the PM₁₀ and ²¹⁰Pb activity concentration, whereas a weak correlation was observed between PM₁₀ and ⁷Be. This is due to the fact that ⁷Be is largely associated with sub-micrometer size particles, whereas PM₁₀ is contributed by larger sizes. The dependence of the activity concentrations of ⁷Be and ²¹⁰Pb with meteorological parameters such as rainfall, temperature, and humidity was studied through linear regression analysis. A significant correlation was observed between ⁷Be and ²¹⁰Pb concentrations with rainfall intensity (with identical correlation coefficients), which suggested that the removal mechanisms of these two radionuclides were similar. ⁷Be showed a strong correlation with temperature, whereas ²¹⁰Pb with humidity. A comparison of the data obtained in the present study for the South West Coast of India with the global literature values of ⁷Be and ²¹⁰Pb in aerosols showed that the values did not reflect the well-known latitudinal dependence of the ⁷Be tropospheric fluxes. Overall, the study provides an improved understanding of the correlation and variability of ²¹⁰Pb and ⁷Be concentrations in the atmosphere in the South West Coast of India.