Archive of Spotlight Feature Articles

Air Resources Laboratory and the Wieliczka Salt Mine

NOAA's Air Resources Laboratory is part of an international team charged with evaluating, restoring and protecting an important "World Heritage" site in Eastern Europe.

Because it contains centuries-old salt carvings, the Wieliczka Salt Mine, near Kraków, Poland, was designated as a site of "outstanding universal value to mankind" under the World Heritage Convention in 1978. The mine was placed on the very first list of endangered World Heritage sites due to the serious threat of deterioration of the historic salt carvings within the mine.

The salt carvings were created over many centuries by the miners and other sculptors, and represent an impressive body of art works within the hundreds of kilometers of mine passages.

(Left) The Kinga Chapel, carved entirely of salt, including the altar (far end), floor tiles, and chandeliers. This area is still in excellent condition.

(Right) A badly deteriorated salt statue in St. Anthony's Chapel. The project goal is to prevent other artworks in the mine from being similarly affected by water vapor.

The deterioration of the salt carvings is due to attack by water, much of which is transported through the air. Salt develops a liquid film on its surface and begins to dissolve when the relative humidity of the surrounding air reaches approximately 75%.

Potential sources of water vapor in the mine include moisture from the forced ventilation system, penetration of ground water, water sources elsewhere in the mine, and even the breath of the hundreds of thousands of visitors who tour the mine each year. Protection of the mine and its artifacts could require different strategies, depending on the moisture source.

It is the first site ever to be removed from the endangered list, thanks in part to the efforts of ARL scientists.

Schematic of Wieliczka Salt Mine ventilation system in the "monumental area" showing flow paths, major chambers and shafts, and monitoring stations.

Under a program funded by the Maria Sklodowska-Curie Joint Fund II, under the auspices of the U.S.-Polish Joint Commission, with additional (later) assistance from the World Heritage Center (under the United Nations Educational, Scientific, and Cultural Organization, UNESCO), a study was carried out within the threatened portion of the Wieliczka Salt Mine to determine the likely source or sources of moisture, and to make recommendations to reduce or eliminate the threat. The collaborating research groups included NOAA's Air Resources Laboratory (ARL), the National Park Service, California Institute of Technology, the Polish Academy of Sciences' Institute for Catalysis and Surface Chemistry, and the Wieliczka Salt Mine.

A Wieliczka engineer installing a NOAA-designed instrument package in St. Anthony's Chapel

A Wieliczka engineer installing a NOAA-designed instrument package in St. Anthony's Chapel, one of the most water-damaged areas of the mine's artworks. The pillars, crucifix, and other carvings are entirely in salt.

The study began in February 1992 when U.S. and Polish scientists installed instruments to monitor conditions (primarily air flow, temperature, and humidity) and air pollutant concentrations in key locations within and above the mine. These instruments remained in place for a full year to assess the daily and seasonal variability of the data, and were operated by the Polish team. The U.S. and Polish teams then worked together to evaluate the information and prepare a report and recommendations for the mine authorities, so that remedial measures (mainly dehumidification of the entering air stream) could be adopted.

A U.S. specialist volunteered to design a huge dehumidification system for the mine, and to develop cost estimates for the equipment. The hardware was purchased under a variety of funding arrangements and installed in the mine's ventilation system. The dehumidification system became operational in the spring of 1998 and ran throughout the summer season. Conditions in the mine were remarkably improved from previous years; a member of the Polish scientific team monitored instruments installed in key areas to provide quantitative data.

Although the dehumidification system is not yet operating exactly as desired, conditions in all mine areas but one have become safe for the sculptures. "Tuning" of the dehumidification system is planned and is expected to completely solve the mine's moisture problem. In view of this considerable success, the World Heritage Commission formally removed the Wieliczka Salt Mine from the list of endangered World Heritage sites in December 1998. It is the first site ever to be removed from the endangered list, thanks in part to the efforts of ARL scientists.

A film documentary is being prepared on the Wieliczka Salt Mine for the National Geographic Society, with special emphasis on the success of the conservation measures developed and applied under Joint Fund auspices. Interviews with the U.S. and Polish scientific team are planned for the spring and summer of 1999.

The Air Resources Laboratory, located in Silver Spring, MD, carries out research on processes that affect the quality of the atmosphere. These processes are related to transport, transformation, and removal of trace substances, including both wet and dry deposition, and the exchange between the atmosphere and biological and non-biological surfaces. Research in all these areas involves physical and numerical studies, leading to the development of air quality simulation models. The Laboratory provides scientific advice to elements of NOAA and other Government agencies on environmental problems and emergency preparedness.

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