Measurements of aerosol particles in the Škocjan Caves, Slovenia.

For the first time, continuous aerosol measurements were performed in the Škocjan Caves, one of the most important cave systems in the world, and listed by UNESCO as a natural and cultural world heritage site since 1986. Measurements of PM10 were performed during three different periods: (1) in December 2011, the average background concentration was found to be about 4 μg m(-3); (2) in June 2012, a higher concentration was measured (8 μg m(-3)); and (3) from 8 to 20 August 2012, the highest concentration of 15.3 μg m(-3) was measured. Based on the PM10 measurement results, and as compared to similar measurements outside the cave, it can be hypothesized that the increase in the cave's aerosol concentration during the summer was connected to both the higher number of visitors and the polluted atmospheric air entering the cave upon entering of the cave system. Additional measurement of nanoparticles with scanning mobility particle sizer spectrometer (size between 14.1 and 710.5 nm) confirmed these findings; during the summer period, a severe raise in the total aerosol concentration of 30-50 times was found when groups of visitors entered the cave. Our results on nanoparticles demonstrated that we were able to detect very small changes and variations in aerosol concentration inside the cave. To our knowledge, these are the first results on nanoaerosol measurements in a cave, and we believe that such measurements may lead to the implementation of better protection of delicate cave systems.