A study of temporal variations of 7 Be and 210 Pb 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 210 Pb and 7 Be 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 7 Be and 210 Pb 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 7 Be occurring in the summer and that of 210 Pb in the winter season. The concentration of both the radionuclides was minimum in the rainy season. Higher 210 Pb 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 7 Be concentration in the air. A clear trend of increased and lowered concentration of 7 Be 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 210 Pb activity concentration, whereas a weak correlation was observed between PM10 and 7 Be. This is due to the fact that 7 Be is largely associated with sub-micrometer size particles, whereas PM10 is contributed by larger sizes. The dependence of the activity concentrations of 7 Be and 210 Pb with meteorological parameters such as rainfall, temperature, and humidity was studied through linear regression analysis. A significant correlation was observed between 7 Be and 210 Pb concentrations with rainfall intensity (with identical correlation coefficients), which suggested that the removal mechanisms of these two radionuclides were similar. 7 Be showed a strong correlation with temperature, whereas 210 Pb 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 7 Be and 210 Pb in aerosols showed that the values did not reflect the well-known latitudinal dependence of the 7 Be tropospheric fluxes. Overall, the study provides an improved understanding of the correlation and variability of 210 Pb and 7 Be concentrations in the atmosphere in the South West Coast of India.