Assessment of Temporal Variations of Natural Radionuclides Beryllium-7 and Lead-212 Concentrations in Surface Air in Tanay, Philippines through the CTBTO Radionuclide Monitoring Station PHP52

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Introduction

Physico-chemical processes occurring in the atmosphere play an important part in the global distribution of radionuclides. The detection of primordial cosmogenic and terrestrial radionuclides in surface air provide researchers the opportunity to understand these processes occurring in the atmosphere as well as to evaluate the total exposure of the public to ionizing radiation. In this study, radionuclide concentrations of cosmogenic and terrestrial radionuclides Beryllium-7 and Lead-212 in surface air and meteorological data collected by the CTBTO Radionuclide Monitoring Station PHP52 in Tanay, Philippines were assessed to understand the atmospheric conditions involved in radionuclide distribution in tropical climates.

Materials and Methods

Air particulate samples were collected daily for 24 hours on a 57cm x 46cm Whatman GF/A glass fiber air filter using a high-volume air sampler located 1.5 meters above ground with a sampling rate of 900- 950 m³ /hr. The collected air filter sample was then compressed to a 5-cm diameter disc using a hydraulic press, placed on a plastic sample holder, and allowed to decay for 24-hours. The sample is then analyzed for 24 hours using a high-purity Germanium (HPGe) gamma spectrometer. Daily activity concentrations of ²¹²Pb and ⁷Be from 2012 to 2017 were retrieved from the CTBTO Concentration Reporting Tool (CRTool), plotted against sample collection date. Radionuclide concentrations and meteorological data were then evaluated for possible correlations.

Results and Discussion

Surface air concentrations of ⁷Be and ²¹²FPb in 2017 were found to range from 0.025 to 9.877 mBq/m³ and from 1.718 to 55.549 mBq/m³ , respectively. Surface air concentrations of ⁷Be and ²¹²FPb show a consistently similar trend annually from 2012 to 2017. Positive and negative correlations were also observed between radionuclide concentrations and meteorological data, supporting observations from other literature regarding the effects of meteorological factors to variations in radionuclide activity concentrations in surface air.

Conclusions

Radionuclide concentrations in surface air are affected by atmospheric conditions such as temperature, humidity, and amount of precipitation, which also varies depending on the season. This is further supported by the observed annual trends on radionuclide activity concentrations which follow the dry and wet season observed in tropical climates such as the Philippines. Analysis of radionuclide concentrations in rainfall collected in the study site could also be considered in the future to further validate the results acquired in this study.