Simultaneous measurement and analysis of radon, air ion, and aerosol concentrations under varying air pollution and meteorological conditions

Radon’s radioactive decay is the primary natural source of small air ions in the near-ground layer of the atmosphere. The exhalation of radon from the soil is influenced by local meteorological conditions, while the reduction in small air ion concentrations is primarily associated with the concentration of aerosol pollutants in the air. The goal of this measurement campaign was to investigate the correlations between these factors across different meteorological conditions and pollution levels. To achieve this, measurements were conducted under distinct meteorological and air pollution conditions at two separate sites. Measurements in clean air conditions were carried out during the early autumn in a suburban area of Belgrade, while measurements in late autumn were conducted in the city center, where high levels of air pollution, low temperatures, and high humidity were present. Simultaneous measurements and correlation analyses were performed on radon concentration, air ions, particle size distribution, cumulative mass concentration (particulate matter, PM), relative humidity, pressure, and temperature. The results revealed substantially lower radon concentrations during late autumn, primarily attributable to the absence of nocturnal thermal inversions and the suppression of radon exhalation caused by elevated soil moisture content. Small air ion concentrations were notably lower, resulting from both reduced radon exhalation and high levels of air pollution, characterized by elevated aerosol concentrations, which is reflected in a high number of ultrafine particles. Additionally, a strong negative correlation was observed between air ion concentration and concentration of ultrafine and fine particles (20 to 650 nm). In contrast, radon concentrations exhibited a clear diurnal pattern during the summer, with nocturnal maxima and daytime minima, while radon levels remained consistently low during the winter.