Abstract
The thoron gas (Rn-220) activity concentration as well as activity size distribution of unattached and attached Pb-212 to aerosol particles was measured in the open air of Jeddah City, Kingdom of Saudi Arabia. An electroprecipitation method was applied for measuring the Rn-220 concentration. A mean activity concentration of Rn-220 was determined to be 1.80 +/- 0.47 Bq m(-3). The unattached activities of Pb-212 were collected using the wire screen diffusion battery technique while a low-pressure cascade impactor collected the attached activities. The mean activity median thermodynamic diameter (AMTD) of unattached Pb-212 was determined to be 1.32 nm with a relative mean geometric standard deviation (sigma(g)) of 1.45. A mean concentration of unattached activity of 212Pb was found to be 9.48 +/- 1.12 mBq m(-3). A mean unattached fraction (f(p)) of 0.028 +/- 0.002 was obtained at a mean aerosol particle concentration of 29 x 103 cm(-3). Sometimes, the f(p) values were less than the detection limit of 0.009. A mean activity median aerodynamic diameter (AMAD) of the accumulation mode of attached 212Pb was determined to be 352 nm with a mean (sigma(g)) of 2.6. The mean value of specific air activity concentration of Pb-212 associated with that mode was determined to be 310 +/- 12 mBq m(-3). With a dosimetric model calculation (ICRP, 1994) the total and regional deposition fractions, total and regional equivalent doses could be evaluated considering the obtained parameters of the activity size distributions. At a total deposition fraction of about 97% of unattached activities the total equivalent dose to the human lung was determined to be 0.16 mu Sv while a total equivalent dose of 0.44 mu Sv was determined at a total deposition fraction of about 23% for the attached activities. It was found that an unattached fraction of f(p) approximate to 13% yields to about 27% of the total equivalent dose. (C) 2014 Elsevier Ltd. All rights reserved.