Global distribution of 7Be, 210Pb and, 210Po in the surface air (with Appendix A-E)

Abstract

In the effort of modelling the global distribution 7Be, 210Pb and 210Po in surface air, the results from exploration of radioactivity exploration from the Arctic to the Antarctic during 1980 to 1996 are compiled with the results reported by other authors. Partial least square regression modelling PLS-regression, predict missing 7Be, 210Pb and 210Po values of air concentration or annual deposition. All available data of air concentration and deposition, of these radionuclides are then correlated with geophysical parameters. The results indicate that the global latitudinal distribution of 7Be air concentration was rather flat, with an overall global average of 4.2 (SE 0.4) mBq.m-3, although with a slight dip at the equator and decrease towards high latitudes. The corresponding latitudinal distribution was also flat, and decreased slightly at high and low altitudes, with overall global average of 7Be annual deposition was 1500 (SE 100) Bq.m-3.a-1. The 7Be deposition rate estimated from reported annual mean air concentration and annual deposition is 13.4 +/- 1.7 (SE) mm.s-1. By using PLS-r modelling of either air concentrations or annual depositions, the average deposition rate of 7Be was estimated to 12.3 +/- 1.6 (SD) mm.s-1. The 7Be deposition-rate don´t vary significantly with longitude, latitude or geometrical average year of sampling date. Linear regression with height, however, is negative with a coefficient of - 0.02. At sea level, the 7Be deposition-rate was estimated to 13 mm.s-1, while at a height of 800 m it was predicted to be 7 mm.s-1. The 16 values of 7Be deposition rate, reported in the literature, are widely scattered (SD = 18) with an average of about 18 mm.s-1. The latitudinal distribution of the activity concentration of 210Pb in air showed a maximum of about 600 +/- 200 micoBq.m-3 around 45 oN with a steady decrease towards higher and lower latitudes. Minimum values of 400 micoBq.m-3 and 80 micoBq.m-3 were estimated at 90 oN and at 90 oS respectively. The latitudinal distribution of all 210Pb air concentration values (micoBq.m-3) is given by the following equation: log10[210Pb] = 2.52 + 0.0083·(Latitude) - 9.87.10-5· (Latitude)2. The latitudinal distribution of all 210Pb annual deposition values (Bq.m-2.a-1) showed a maximum of about 200 +/- 100 Bq.m-2.a-1 around 45 oN, with a steady decrease towards higher and lower latitudes. A minimum of 100 Bq.m-2.a-1 was predicted at 90 oN, although a value of 17 +/- 4 Bq.m-2.a-1 has been recorded at 84.4 oN 2.3 oW. At 90 oS the predicted 210Pb annual deposition was 3 Bq.m-2.a-1. The 210Pb deposition rate was estimated 12.5 +/- 0.7 mm.s-1 with no significant variation with latitude, height, or average of interval of sampling date. With longitude, however, the 210Pb deposition rate varied significantly (linear k=0.02) R=0.99. The values of 210Po air concentration around 20 - 45 oN ranged between 50 – 1000 micoBq.m-3 with a mean of 200 micoBq.m-3, and the 210Po annual deposition ranged between 20-800 Bq.m-2.a-1 with a mean of 100 Bq.m-2.a-1. The longitudinal distribution of the 210Po/210Pb activity ratios follow a narrow linear relation from 0.2 at 90 oW to 1.0 at 170 oE. While the 210Po air concentration and annual deposition are widely distributed along the longitudes with a slight decrease west of the Greenwich meridian.