Abstract Rationale Respiratory diseases caused by exposure to the respirable fraction of particulate matter (PM) are a major public health concern, particularly in areas with elevated air pollution. Fine suspended particles with an aerodynamic diameter below 10 µm, especially those smaller than 4 µm, can reach the distal regions of the respiratory tract and pulmonary alveoli, triggering inflammatory and fibrotic processes. Prolonged exposure to respirable particles contributes to chronic respiratory conditions, including chronic obstructive pulmonary disease (COPD), and asthma, while also increasing susceptibility to infections and impairing lung function. Recent research has increasingly focused on natural environments that may exert protective or regenerative effects on the respiratory system, such as saline microclimates utilized in subterraneotherapy. A well-documented example of such an environment is the “Wieliczka” Salt Mine in southern Poland where is the presence of saline aerosol containing microdroplets of NaCl and other mineral salts. Inhalation of this aerosol supports airway cleansing, mucus liquefaction, and the mitigation of mucosal inflammation. Consequently, therapeutic stays in underground salt chambers are used as supportive treatment for COPD, bronchial asthma, and recurrent bronchitis. Materials and Methods The present study aimed to quantitatively and qualitatively assess respirable fractions of suspended particles, nitrogen dioxide (NO2), and volatile organic compounds (VOCs) in the underground air of the “Wieliczka” Salt Mine and to compare these parameters with outdoor atmospheric air. Additionally, the potential dose of dry saline aerosol inhaled by patients was estimated. Measurements were conducted using high-resolution Palas particle analyzers. Results Results demonstrated that mean PM1 and PM2.5 concentrations in underground chambers were significantly lower than in outdoor air. Fine fractions (PM1-PM4) comprised approximately 80% of the total aerosol mass, and chemical analysis confirmed the predominance of NaCl particles, indicating their mineral and saline origin. The indoor-to-outdoor (I/O) ratio revealed internal sources of coarser particles (mean I/O for PM4 2.12 while for PM1 is 0.64), while no significant internal sources of fine particles were detected. In contrast, NO2 and total VOCs concentrations were influenced exclusively by external sources, with no evidence of accumulation underground. Conclusions These findings indicate that the microclimate of the “Wieliczka” Salt Mine exhibits highly favorable aerosol characteristics, combining low particulate pollution with the presence of natural saline aerosol with potential therapeutic effects. The study supports the use of the mine as a model of a health-promoting subterranean microclimate and underscores its scientific relevance for respiratory rehabilitation and subterraneotherapy. This abstract is funded by: Research was funded by Warsaw University of Technology within the Excellence Initiative: Research University (IDUB) programme, POSTDOC VI
Badyda et al. (Fri,) studied this question.