Atmospheric residence times and excess of unsupported Po in aerosol samples from the Kuwait bay-northern gulf.

The concentration of cosmogenic radionuclide Be and the naturally occurring radionuclide Rn and its progenies Pb, Po, and Pb were measured in the ground surface air in the urban area of the northern Arabian Gulf close to Kuwait Bay. A high-volume air sampler connected with a five-stage cascade impactor was used to collect approximately 1800 cubic meter weekly for a period of one year. The concentrations of Pb and Po varied from 0.35 to 1.65 mBq m and from 0.23 to 3.2 mBq m, respectively; the Po/Pb activity ratio was close to one. The average concentration of Be was 6.24 mBq m, ranging from 3 to 10 mBq m. The temporal variations of Pb, Po and Be showed maximum concentrations of Po and Be in occurred summer months. The observed excess of Po concentrations can be attributed to the local and long-range transport of suspended dust with Pb and Po in radioactive equilibrium state, oil industry emissions, local resuspended dust and the sea-salt-aerosols from the Arabian Gulf. The range of the residence time estimation using the Rn/Pb and Pb/Pb activity ratio methods ranged from three to five days. Moreover, the estimated residence time by the application of Be from the activity median aerodynamic diameter method was 4.2 days. The method of using the Po/Pb activity ratio was invalid because of the excess Po sources of anthropogenic origin. Therefore, extensive accurate diurnal measurements of Pb and Rn can be applied in hot arid regions for better aerosols residence time estimation.