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Measurements of alpha and beta radiations carried out in Ibadan (Nigeria) are presented. Activity of alpha radiation in the air is much lower than that of beta. The mean daily activity (Bq) ranged from 0.013 to 0.075 for alpha and from 1.475 to 76.136 for beta throughout the periods of investigation which include wet, dry and harmattan periods. The highest activity occurred during harmattan followed by wet period and the least was during the dry period. The harmattan dust originating from the Sahara desert is found to be radioactive. During wet period the aerosols and the condensation nuclei present in the atmosphere were also found to be radioactive to some extent. Background beta (beta) and alpha (alpha) activities were found to have increased greatly over those earlier reported in the period between 1986/1987-2001/2002. Beta activity has two peaks at 19 and 6 h LT while the peak time of alpha activity varies randomly throughout the periods of observation. The minima activities of alpha and beta occur throughout the day. The results showed that ambient alpha and beta activities were highly correlated to atmospheric potential gradient. (c) 2005 Elsevier Ltd. All rights reserved.