Coagulation effect on the activity size distributions of long lived radon progeny aerosols and its application to atmospheric residence time estimation techniques

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.