Properties of Particulate Matter in the Air of the Wieliczka Salt Mine and Related Health Benefits for Tourists.

This study aimed to evaluate the mass concentration of size-resolved (PM 1 , PM 2.5 , PM 4 , PM 10 , PM 100 ) particulate matter (PM) in the Wieliczka Salt Mine located in southern Poland, compare them with the concentrations of the same PM fractions in the atmospheric air, and estimate the dose of dry salt aerosol inhaled by the mine visitors. Measurements were conducted for 2 h a day, simultaneously inside (tourist route, passage to the health resort, health resort) and outside the mine (duty-room), for three days in the summer of 2017 using DustTrak DRX devices (optical method). The highest average PM concentrations were recorded on the tourist route (54-81 µg/m 3 ), while the lowest was in the passage to the health resort (49-62 µg/m 3 ). At the same time, the mean outdoor PM concentrations were 14-20 µg/m 3 . Fine particles constituting the majority of PM mass (68-80%) in the mine originated from internal sources, while the presence of coarse particles was associated with tourist traffic. High PM deposition factors in the respiratory tract of children and adults estimated for particular mine chambers (0.58-0.70), the predominance of respirable particles in PM mass, and the high content of NaCl in PM composition indicate high health benefits for mine visitors.