Variation in indoor thoron levels in Mexico City dwellings

This paper presents the results obtained for thoron concentration in 50 single-family dwellings in normal occupancy conditions (open house conditions), measured by a passive electret system (type E-PERM, SSTB configuration) in a 2001-2002 monitoring survey in the Metropolitan Zone of Mexico City. The results show the general log-normal distribution of integrated indoor thoron concentration with annual arithmetic and geometric means of 82 and 55 Bq m-3, respectively, with ranges from 8 to 234 Bq m-3 higher than world average of 3 Bq m-3. The seasonal variation shows the minimum mean values in the summer season that were 35% lower than in autumn. (authors)