Air Pollutant Intrusion into the Wieliczka Salt Mine

The Wieliczka Salt Mine, located in southern Poland near the city of Krakow, has been worked as a source of rock salt since the late 13th century. The mine consists of over 200 km of underground passages, connecting more than 2000 excavation chambers on 9 underground levels extending down to 327m below the surface, see diagram . Over the centuries, miners have established a tradition of carving sculptures out of the native rock salt. As a result, the mine contains entire underground churches, altars, bas-reliefs, and dozens of life-size or larger statues. It also houses an underground museum and has a number of special purpose chambers such as a sanatorium for people suffering from respiratory ailments. The largest of the chapels, the Chapel of the Blessed Kinga, is located 101 meters below the surface, it is over 50 meters long, 15 meters wide, 12 meters high, with a volume of 10,000 cubic meters. As a testament to its historical and artistic importance, the mine has been placed on UNESCO's World Heritage List of sites designated as having ``outstanding universal value to mankind.'' It receives up to a million visitors yearly, most of them during the warmer summer months.

Today, many of the salt sculptures are slowly dissolving. Water vapor present in the ventilation air in the mine is being absorbed into the rock salt at several locations in the mine, causing erosion of the carved salt surfaces. A joint team of Polish and American scientists and engineers are conducting experiments in the mine to document the environmental conditions there and to seek solutions to the water vapor condensation problem. One question faced by the study team is whether or not there is any significant soiling or chemical attack on the statuary that might alter the hygroscopic character of the salt.

Rock salt develops a liquid film on its surface and begins to dissolve when the relative humidity of the surrounding air reaches approximately 75%. This is known as the relative humidity of deliquescence. Airborne ionic substances (e.g., nitrates) having relative humidities of deliquescence below that of rock salt could deposit onto the sculptures to an extent that the deliquescence point of the salt surface is lowered. If this occurs, it would influence the selection of a future dehumidification system for the mine.

The purpose of our current research is to examine the transport of air pollutants from the outdoor atmosphere into the mine, and the subsequent deposition of those pollutants onto the surfaces in the mine, with an eye toward determining whether or not the deliquescence point of the salt would be significantly affected by the pollutant deposition processes. Filter-based air sampling methods are used to determine the concentration and chemical composition of airborne particles in both fine and coarse particle size ranges, as well as the concentrations of selected reactive gases: sulfur dioxide (SO2), nitrogen dioxide (NO2), nitric acid (HNO3), and hydrochloric acid (HCl). Deposition plates and scrapings taken from surfaces in the mine also are used for studying particulate plus gas-phase pollutant deposition to surfaces. These measurements reveal the chemical and physical nature of the pollutants present, the rate of pollutant accumulation on surfaces, and whether or not there are significant differences in pollutant concentration from one chamber to another throughout the mine.


More information about Wieliczka:

Our scientific paper in Environmental Science and Technology

Complete reference information.

Lynn Salmon <>{

Last updated: July 2, 2013