This preliminary study examines the seasonal distribution and correlation of negative air ionization near waterfalls situated on two types of geological substrates, and its relationship to water properties such as electrical conductivity (EC), total dissolved solids (TDS), salinity, and water temperature. Measurements were conducted between 2022 and 2024 at six waterfalls in the Stara Planina Mountain. Five waterfalls, Tupavica, Draganov Vir, Tri Kladenca, Donji Piljski, and Grujin, are located on Triassic and Permian sandstones. The sixth, Bigar waterfall, is located on limestone and exhibits characteristics typical of waterfalls formed on carbonate substrates. The results indicate that the underlying geology significantly influences variations in airborne anion concentrations. Waterfalls on sandstone substrates exhibit much higher levels of negative ionization compared to those on limestone. This contrast appears to be linked to water chemistry: sandstone-based waterfalls tend to have lower values of dissolved solids and EC, whereas limestone waterfalls display higher concentrations. These findings contribute to understanding the “waterfall effect” and highlight how geological and environmental factors shape the generation of natural air ionization. Such insights can inform the selection of natural sites for eco-tourism, wellness retreats, and health-oriented infrastructure where exposure to high negative ion concentrations is beneficial.
