Tuesday, June 26, 2007

Radionuclides in Aerosols

7Be and 210Pb are the natural radionuclides present in the atmosphere. Several studies have shown that useful information about transport, removal and residence time of aerosols in the atmosphere can be obtained from the measurements of 7Be and 210Pb. 7Be (half-life = 53.3 days) is produced by cosmic ray spallation of nitrogen and oxygen primarily in lower stratosphere and upper troposphere. Therefore, 7Be is used as a tracer of stratospheric or high tropospheric sources such as ozone, stratospheric bomb fallout debris, stratospherically injected volcanic components. In contrast, 210Pb (half-life = 22.3 years) is a progeny of 238U. The source of 210Pb is radioactive decay of 222Rn (half-life = 3.8 days), a noble gas, continuously emitting from soils to the atmosphere. Thus, 210Pb is a tracer of continental air as more than 99% 222Rn is emanating from the surface of continents. Half-life of both the radionuclides are long enough with respect to their residence time in the lower atmosphere, therefore the principal removal pathway of the 7Be and 210Pb is via dry and wet deposition rather than radioactive decay. Since the sources of 7Be and 210Pb are well established and different in terms of altitude, their simultaneous study provides useful information about the vertical and horizontal mixing of air masses in the atmosphere. For further study, please see the following references and references therein.

Balkanski, Y. J., D. J. Jacob and G. M. Gardner (1993), Transport and residence times of tropospheric aerosols inferred from a global three-dimensional simulation of 210Pb, J. Geophy. Res., 98, 20573–20586.

Graustein, W. C. and K. K. Turekian (1996), 7Be and 210Pb indicate an upper troposphere source for elevated ozone in the summertime subtropical free troposphere of the eastern North Atlantic, Geophys. Res. Lett., 23, 539-542.

Gaffney, J. S., N. A. Marley and M. M. Cunningham (2004), Natural radionuclides in fine aerosols in the Pittsburgh area, Atmos. Environ., 38, 3191-3200.

Lee, H. N., L. Tositti, X. Zheng, and P. Bonasoni (2007), Analyses and comparisons of variations of 7Be, 210Pb, and 7Be/210Pb with ozone observations at two Global Atmosphere Watch stations from high mountains, J. Geophys. Res., 112, D05303, doi:10.1029/2006JD007421.

1 comment:

Silvia Alonso-Pérez said...

About 40K y 137Cs and aerosols:

Hernández, F., Alonso-Pérez, S., Hernández-Armas, J. y Cuevas, E. (2005). Influence of major African dust intrusions on the 137Cs and 40K activities in the lower atmosphere at the Island of Tenerife. Atmospheric Environment, 39, 4111-4118