Diurnal variations of indoor short-lived radon daughters with positive 218Po and 214Pb clusters and their impact on atmospheric air ions

Airborne radon progenies (²¹⁸Po, ²¹⁴Pb and ²¹⁴Po) are classified as radioactive aerosols and pose a significant public health risk when inhaled indoors. They are the largest source of natural radiation exposure and play a key role in environmental ionization, affecting aerosol size distribution. Thus, accurate measurements of these contaminants are crucial for understanding and controlling airborne radioactivity, providing basic parameters for assessing atmospheric air pollution levels. Therefore, continuous indoor measurements were conducted at 2-h intervals across various seasons during 2023 and 2024 in El Jadida, Morocco, considering meteorological parameters. The measurement method involves sampling the aerosol-attached radon progeny on filters, followed by α-counting using nuclear track detectors (CR-39) based on a three-count approach. Additionally, we have developed PC-based software that utilizes experimental measurements as input data to solve differential equations and calculate all necessary physical quantities. The ²²²Rn, ²¹⁸Po, ²¹⁴Pb and ²¹⁴Po annual average concentrations were 80.2 ± 6.6, 44.0 ± 3.6, 34.5 ± 2.8, and 24.3 ± 2.0 Bq/m³, respectively, with ²¹⁸Po and ²¹⁴Pb unattached activity of 11.2 and 0.6 Bq/m³. These concentrations exhibited significant diurnal variations of 3–4 times with maxima in the early morning and minima in the afternoon, while they changed seasonally by 30–50 % with peaks occurring in the colder months. Diurnal variations in radon-linked ionization rates and corresponding air ion concentrations are subject to changes in these radionuclides levels, with annual averages of 27.9 ion-pairs cm⁻³ s⁻¹ and 2113 ions/cm³ respectively. Results indicated that, under normal home conditions, about 52 % of ²¹⁸Po and 49 % of ²¹⁴Pb clusters are positively charged.