Unattached fraction and size distribution of aerosol-attached radon progeny in the open air

Unattached fractions of the radon progeny 218Po and 214Pb, size distributions for both unattached 218Po and 214Pb, and attached 214Pb and 214Bi, along with condensation nuclei (aerosol-particle concentrations), were measured in the open air of the city of El-Minia, Egypt. The measurements were performed with a wire-screen diffusion battery and a low-pressure Berner cascade impactor using standard methodologies. The results for parameters of derived distributions demonstrate that the distributions for the former (unattached 218Po and 214Pb) are nearly similar. The diffusion equivalent diameters (df) of 218Po and 214Pb were determined to be 1.4 and 1.55 nm with relative geometric standard deviations (σg) of 1.65 and 2.1, respectively. The latter distribution (attached 214Pb and 214Bi) are nearly identical. Most of the activities were associated with the aerosol particles of the accumulation mode. The mean activity median aerodynamic diameters (AMAD) of 214Pb and 214Bi have the same value of 380 nm but the relative geometric standard deviation of the log-normal distribution of 214Pb shows a broader activity distribution than 214Bi (σg=2.2 for 214Pb and σg = 2.05 for 214Bi). (Author)