Radiation Protection Dosimetry (2014), Vol. 160, No. 1–3, pp. 65 –69 Advance Access publication 4 April 2014
doi:10.1093/rpd/ncu097
TEMPORAL VARIABILITY OF RADON IN THE ATMOSPHERE ´ KARST CAVES (SLOVAKIA) ˇ ECKA OF DOMICA AND VAZ
*Corresponding author: [email protected] Continual monitoring of radon activity concentration was performed in two caves: Domica and Vazˇecka´. Radon in the air of the Domica cave was monitored from June 2010 to July 2011. Radon research in the Vazˇecka´ cave started in June 2012 and it is still being carried out. Radon concentration in cave atmosphere exhibited seasonal, short-term and daily variations. Daily average of radon in Domica varied from 0.5 to 2.7 kBq m23. Seasonal trend was characterised by the highest concentration in September and the lowest from February to March. Radon concentration in the Vazˇecka´ cave was significantly higher, and the daily average ranged from 1.0 to 5.3 kBq m23. The highest values were registered from June to September and in January. The seasonal and daily variations of 222Rn activity concentration in the atmosphere of both caves are assumed to be associated with the atmospheric temperature. No effect of atmospheric pressure on radon short-term variation was found.
INTRODUCTION Radon concentration in underground environments usually exhibited significant temporal variations. The seasonal pattern with the maximum in summer and minimum in winter is often observed in caves or underground tunnels and galleries(1 – 5). This temporal variation can be explained by the annual variation of natural ventilation, governed by air movement caused by the difference in external and internal air densities, controlled mainly by air temperature. However, also the seasonal variations of a different character were observed, with the maximum in autumn and minimum in summer and winter(6) or with the maximum in winter and minimum in summer(7). Short-term variations of radon in underground openings were sometimes associated with atmospheric pressure changes(4, 7) or rainfall(7). In Slovakia, the first long-term radon research in show caves was realised in the years 1992–93(8), using an integral method. The first continual radon monitoring was conducted from June 2006 to October 2011 in the Driny cave(9). In this paper, the preliminary results of the continual high-resolution radon research and the annual effective dose estimate for a cave guide in the Domica and Vazˇecka´ show caves are presented. SITE DESCRIPTION AND METHODS Continual high-resolution monitoring of radon activity concentration was performed in two show caves: Domica and Vazˇecka´. The Domica cave is situated in
the Slovak Karst National Park, Southern Slovakia. The cave is formed in the Middle Triassic pale Wetterstein limestone of the Silica Nappe along the tectonic faults by corrosive and erosive activities of Styx and Domica Brook and smaller underground tributaries draining waters mainly from the non-karst part of the catchment. Air temperature ranges from 10.2 to 11.4 8C and relative humidity from 95 to 98 %. The cave is mainly horizontal, connected to the ˇ ertova diera cave, and they together reach a length C of 5358 m. They also form one genetic unit with the Baradla cave in Hungary with a total length of 25 km, from which almost one quarter is in the Slovak territory. The cave entrance/exit is at an altitude of 339 m. The Vazˇecka´ cave located in the Vazˇec karst, Northern Slovakia, is developed in the Middle Triasic dark-grey Gutenstein limestone of the Biely Va´h Series of the Chocˇ Nappe, by ancient ponor waters of the Biely Va´h side branch. The cave length is 530 m, the entrance/exit is at an altitude of 784 m. Air temperature ranges between 6.5 and 7.1 8C, relative humidity between 94 and 96 %. Radon monitoring in both caves was performed using the Barasol detector (Algade, France) based on alpha particle detection. Impulses were recorded every 10 min. In the Domica cave, three stable monitoring stations equipped with an automatic measuring and registration instruments for continual microclimatic, hydrological and hydrochemical monitoring were installed and operated by the Microstep-MIS company(10). Radon
# The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at Universitaetsbibliothek Giessen on June 15, 2015
I. Smetanova´1,*, K. Holy´2, J. Zelinka3 and J. Omelka4 1 Geophysical Institute, Slovak Academy of Sciences, Du´bravska´ cesta 9, Bratislava 845 28, Slovakia 2 Department of Nuclear Physics and Biophysics, Faculty of Mathematics, Physics and Informatics, Comenius University, Mlynska´ dolina, Bratislava 842 48, Slovakia 3 State Nature Conservancy of the Slovak Republic, Slovak Caves Administration, Hodzˇova 11, Liptovsky´ Mikula´sˇ 031 01, Slovakia 4 ˇ avojske´ho 1, Bratislava 841 04, Slovakia MicroStep-MIS, C
´ ET AL. I. SMETANOVA
seasonal, daily and short-term variations. The character of seasonal variation was different (Figure 1). Seasonal trend in Domica cave was characterised by the highest radon concentration in September and the lowest from February to March. Hourly average of radon activity concentration varied between 90 and 4700 Bq m23. However, values from 500 to 2000 Bq m23 prevailed in the data set (90 %). In the Vazˇecka´ cave, the highest values were registered from June to September 2012 and in January 2013. The hourly average of radon activity concentration varied between 700 and 5800 Bq m23. During the summer months, radon activity concentration was relatively stable, in the rest of the year short-term variations occurred. The character of the short-term variations in both investigated caves was similar; however, they occurred in a different part of a year. Short-term variations were non-periodic, lasting 4–13 d. Using linear regression of radon time series, no connection with atmospheric temperature or atmospheric pressure variations was confirmed. Based on measured radon data and the exact time a cave guide spent in the cave, provided by the cave stuff, the annual effective dose for a cave guide was assessed, using an equilibrium factor for a cave of F ¼ 0.5(12) and a dose conversion factor of 9 nSv (Bq H m23)21(13). The annual effective dose for a guide in the Domica cave is estimated up to 2 mSv. In months with the highest radon activity concentration (July –October), a visitor receives an effective dose of 5.7 mSv during a tour lasting 1 h. In the Vazˇecka´ cave, the annual effective dose for a cave guide is higher, up to 6 mSv. The effective dose received by a visitor in
RESULTS Radon activity concentration in the Vazˇecka´ cave was significantly higher than in Domica. Daily average of radon activity concentration in the Vazˇecka´ cave ranged from 900 to 5300 Bq m23, and in the Domica cave it varied between 500 and 2700 Bq m23. Radon activity concentration in the atmosphere of both the Domica and Vazˇecka´ caves exhibited
Figure 1. Seasonal variation of 222Rn activity concentration (hourly averages) in the Vazˇecka´ and Domica caves.
66
Downloaded from http://rpd.oxfordjournals.org/ at Universitaetsbibliothek Giessen on June 15, 2015
was monitored from June 2010 to July 2011, at the station at the Virgin passage, situated away from the tourist route. Among others, the internal air temperature, CO2 content and wind speed and wind direction were continually monitored there. The meteorological station situated near the cave includes sensors for measuring of air temperature, relative humidity, wind speed, wind direction, global radiation, rainfall amount and evaporation. Atmospheric pressure data were obtained from the meteorological station of Slovak Hydrometeorological Institute in Kosˇice, 80 km NE from the Domica cave. Radon research in the Vazˇecka´ cave started in June 2012 and it is still being carried out. A detector is placed at the most distant place from the entrance, named Gale´ria, which is part of the tourist route. The Gale´ria is the highest as well as the warmest part of the cave(11). The internal air temperature, CO2 content, humidity, wind speed and wind direction are also monitored there. Atmospheric temperature and pressure values were taken from meteorological station operated by the Geophysical Institute of Slovak Academy of Sciences in Stara´ Lesna´, 40 km NE of the Vazˇec village.
TEMPORAL VARIABILITY OF RADON
months with the highest radon activity concentration (June–September) is 7.8 mS during a visit lasting 25 min. Domica cave The internal wind speed measured in the Virgin passage exhibited clear daily variations that documented the changes of air flow in the cave during the day. Wind speed was low, typically ,0.2 m s21, but occasionally reached up to 0.4 m s21(14). The internal air temperature of the cave at the Virgin passage ranged from 9 to 11 8C and it was markedly affected by rainfall(14, 15). In summer months, the air exchange rate between cave environment and outside atmosphere was low. From June to August, relative stable radon values were recorded, mainly in the interval 500 –1500 Bq m23. The influence of air flow on radon values and radon daily variations was not observed. The inside air movement was recorded exclusively after rainfall and it does not affect radon activity concentration values in the cave atmosphere. The daily variations of radon activity concentration in underground environment are most pronounced when the difference between internal air temperature of the cave and atmospheric temperature changed its sign over 24 h. Diurnal radon variations in the Domica cave were observed predominantly in spring and autumn months. The largest amplitudes of daily radon variations up to 2300 Bq m23 were registered from September to October, when air movement was observed mainly from 6 p.m. to 6 a.m. (Figure 2). In this part of the day, the temperature of outside air was lower than inside the cave. Air of lower activity flowed into the cave and radon activity concentration in the Virgin passage decreased due to the natural
Vazˇecka´ cave The former microclimatology research in the Vazˇecka´ cave(11) proved that air masses and environmental conditions at the measuring point Gale´ria are stable. The entrance door is flush fitting and there is no other entrance or crack connecting the cave with the outdoor atmosphere. A weak air flow was registered only when visitors entered the cave; however, no impact on radon variations was found. No air movement was registered during December and January, as well as on Mondays, when the cave was closed to the public. Air movement in January was registered solely in days when paleontological research was performed there.
Figure 2. Diurnal variation of radon, the difference in internal and external air temperatures and wind direction in the Virgin passage in autumn season.
67
Downloaded from http://rpd.oxfordjournals.org/ at Universitaetsbibliothek Giessen on June 15, 2015
ventilation. The measured wind direction was NW, air ˇ ertova was drawn to the Virgin passage from the C diera cave. Contrary, when the difference between internal and atmospheric temperature was negative, the air flowed into the cave stopped and radon activity concentration increased again (Figure 2). In winter months, the outside air temperature was lower than the temperature of cave atmosphere during the whole day (Figure 3). A continual flow of atmospheric air into the cave proceeded permanently and the cave was naturally ventilated. It resulted in a distinct decrease in radon activity concentration in comparison with the rest of the year. From January to March, measured values ranged mostly between 300 and 1100 Bq m23. In days, when the air flow was weak, an immediate increase of radon was observed as a result of radon exhalation from the rock. As the air flow started again, a steep radon decrease was registered (Figure 3).
´ ET AL. I. SMETANOVA
Figure 4. Seasonal variation of radon and the difference in internal and external air temperatures in the Vazˇecka´ cave.
Despite the cave being well isolated from the outside environment, radon activity concentration exhibited significant temporal variations (Figure 4). From April to the end of October, the atmospheric temperature was higher than the temperature of the internal atmosphere. Natural ventilation of the cave was negligible and radon reached high and relatively stable values, hourly averages ranged mainly from 4000 to 5000 Bq m23. From November to March, the temperature of cave atmosphere was higher than the outside air temperature and radon concentration decreased. Low radon level was disturbed by the significant short-term variations, and they appeared when the temperatures of internal and outside air were equal (Figure 4). Several short-term radon increases followed a preceding rainfall event (Figure 5). After a significant rainfall, part of the cave situated close to the Gale´ria was often flooded, because of an increased underground water
level. As the water level in the cracked rock environment rose, it probably pushed radon-rich air from the rock cracks to the cave atmosphere and it could influence radon concentration in cave atmosphere. The largest amplitudes of radon daily variations up to 1000 Bq m23 were registered in summer months. In winter, the daily variations were absent. The seasonal and daily cycles of radon activity concentration seemed to be connected with the atmospheric temperature changes. CONCLUSIONS In both examined caves, a significant temporal variation of 222Rn activity concentration was found, although the Vazˇecka´ cave is well isolated from an outside atmosphere. The character of seasonal variation was different. In the Domica cave, the maximum was registered in 68
Downloaded from http://rpd.oxfordjournals.org/ at Universitaetsbibliothek Giessen on June 15, 2015
Figure 3. Diurnal variation of radon, the difference in internal and external air temperatures and wind direction in the Virgin passage in winter season.
TEMPORAL VARIABILITY OF RADON
September and minimum in February and March, and in the Vazˇecka´ cave, the maximum was observed in summer months and minimum in winter. The seasonal and daily variations of 222Rn activity concentration are assumed to be associated with the atmospheric temperature changes. No effect of atmospheric pressure on radon short-term variation was found. In the Vazˇecka´ cave, some of radon short-term variations may be associated with the rainfall events.
7.
8.
9.
FUNDING This study was supported by Scientific Grant Agency of Ministry of Education of Slovak Republic (VEGA project 2/0135/12).
10.
REFERENCES
11.
1. Duen˜as, C., Ferna´ndez, M. C., Can˜ete, S., Carretero, J. and Liger, E. 222Rn concentrations, natural flow rate and the radiation exposure levels in the Nerja Cave. Atmos. Environ. 33, 501– 510 (1999). 2. Przylibski, T. A. Radon concentration changes in the air of two caves in Poland. J. Environ. Radioact. 45, 81– 94 (1999). 3. Barbosa, S. M., Zafrir, H., Malik, U. and Piatibratova, O. Multi-year to daily radon variability from continuous monitoring at the Amram tunnel, southern Israel. Geophys. J. Int. 182(2), 829– 842 (2010). 4. Perrier, F. and Richon, P. Spatiotemporal variation of radon and carbon dioxide concentrations in an underground quarry: coupled processes of natural ventilation, barometric pumping and internal mixing. J. Environ. Radioact. 101, 279– 296 (2010). 5. Gregoricˇ, A., Zidansˇek, A. and Vaupoticˇ, J. Dependance of radon levels in Postojna Cave on outside air temperature. Nat. Hazards Earth Syst. Sci. 11, 1523–1528 (2011). 6. Whittlestone, S., James, J. and Barnes, C. The relationship between local climate and radon concentrations in
12.
13.
14.
15.
69
the Temple of Baal, Jenolan Caves, Australia. Helictite, 38(2), 39–44 (2003). Lario, J., Sa´nchez-Moral, S., Can˜averas, J. C., Cuezva, S. and Soler, V. Radon continuous monitoring in Altamira Cave (northern Spain) to assess user´s annual effective dose. J. Environ. Radioact. 80, 161–174 (2005). ˇ urcˇ´ık, M. and Nikodemova´, D. Vicˇanova´, M., D Sledovanie vy´skytu rado´nu v podzemny´ch pracovny´ch priestoroc Radon monitoring in underground working places. In: Proceedings of the Conference Ra´dioaktivita v zˇivotnom prostredı´, Spisˇska´ Nova´ Ves, Slovakia, 21– 22 October, pp. 42– 44 (1997) (in Slovak). Briestensky´, M., Thinova´, L., Stemberk, J. and Rowberry, M. D. The use of caves as observatories for recent geodynamic activity and radon gas concentrations in the Western Carpathians and Bohemian Massif. Radiat. Prot. Dosim. 145, 166– 172 (2011). Gazˇ´ık, P., Haviarova´, D. and Zelinka, J. Integrovany´ monitorovacı´ syste´m jasky´nˇ/integrated monitoring system of caves. Aragonit 14/2, 109– 112. (2009) (in Slovak). Zelinka, J. Thermodynamic characteristic of the Vazˇecka´ cave. In: Proceedings of the Conference Vy´skum, vyuzˇ´ıvanie a ochrana jasky´nˇ 3, Stara´ Lesna´, Slovakia, 14– 16 November, pp. 123–131 (2001) (in Slovak). Gillmore, G. K., Phillips, P., Denman, A. J., Sperrin, M. and Pearce, G. radon levels in abandoned metalliferous mines, Devon, Southwest England. Ecotoxicol. Environ. Saf. 49, 2819– 2292 (2000). United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). Sources and effects of ionizing radiation. Report to the General Assembly, with Scientific Annexes. Vol. 1 (New York: UNSCEAR United Nations) (2000). Smetanova´, I., Holy´, K., Zelinka, J., Omelka, J. and Jurcˇa´k, D. Sezo´nna zmena objemovej activity rado´nu v ovzdusˇ´ı jaskyne Domica/seasonal change of radon activity concentration in the air of the Domica cave. Aragonit 17(1– 2), 24–27 (2012) (in Slovak). Zelinka, J. Posu´denie vplyvu prı´rodny´ch a antropoge´nnych faktorov na zmeny mikroklimaticke´ho rezˇimu jaskyne Domica/examination of the influence of antropogenic factors on the microclimatic regime changes in the Domica cave. Aragonit 8, 17–20 (2003) (in Slovak).
Downloaded from http://rpd.oxfordjournals.org/ at Universitaetsbibliothek Giessen on June 15, 2015
Figure 5. Rainfall events and radon short-term variations in the Vazˇecka´ cave.
doi:10.1093/rpd/ncu097
TEMPORAL VARIABILITY OF RADON IN THE ATMOSPHERE ´ KARST CAVES (SLOVAKIA) ˇ ECKA OF DOMICA AND VAZ
*Corresponding author: [email protected] Continual monitoring of radon activity concentration was performed in two caves: Domica and Vazˇecka´. Radon in the air of the Domica cave was monitored from June 2010 to July 2011. Radon research in the Vazˇecka´ cave started in June 2012 and it is still being carried out. Radon concentration in cave atmosphere exhibited seasonal, short-term and daily variations. Daily average of radon in Domica varied from 0.5 to 2.7 kBq m23. Seasonal trend was characterised by the highest concentration in September and the lowest from February to March. Radon concentration in the Vazˇecka´ cave was significantly higher, and the daily average ranged from 1.0 to 5.3 kBq m23. The highest values were registered from June to September and in January. The seasonal and daily variations of 222Rn activity concentration in the atmosphere of both caves are assumed to be associated with the atmospheric temperature. No effect of atmospheric pressure on radon short-term variation was found.
INTRODUCTION Radon concentration in underground environments usually exhibited significant temporal variations. The seasonal pattern with the maximum in summer and minimum in winter is often observed in caves or underground tunnels and galleries(1 – 5). This temporal variation can be explained by the annual variation of natural ventilation, governed by air movement caused by the difference in external and internal air densities, controlled mainly by air temperature. However, also the seasonal variations of a different character were observed, with the maximum in autumn and minimum in summer and winter(6) or with the maximum in winter and minimum in summer(7). Short-term variations of radon in underground openings were sometimes associated with atmospheric pressure changes(4, 7) or rainfall(7). In Slovakia, the first long-term radon research in show caves was realised in the years 1992–93(8), using an integral method. The first continual radon monitoring was conducted from June 2006 to October 2011 in the Driny cave(9). In this paper, the preliminary results of the continual high-resolution radon research and the annual effective dose estimate for a cave guide in the Domica and Vazˇecka´ show caves are presented. SITE DESCRIPTION AND METHODS Continual high-resolution monitoring of radon activity concentration was performed in two show caves: Domica and Vazˇecka´. The Domica cave is situated in
the Slovak Karst National Park, Southern Slovakia. The cave is formed in the Middle Triassic pale Wetterstein limestone of the Silica Nappe along the tectonic faults by corrosive and erosive activities of Styx and Domica Brook and smaller underground tributaries draining waters mainly from the non-karst part of the catchment. Air temperature ranges from 10.2 to 11.4 8C and relative humidity from 95 to 98 %. The cave is mainly horizontal, connected to the ˇ ertova diera cave, and they together reach a length C of 5358 m. They also form one genetic unit with the Baradla cave in Hungary with a total length of 25 km, from which almost one quarter is in the Slovak territory. The cave entrance/exit is at an altitude of 339 m. The Vazˇecka´ cave located in the Vazˇec karst, Northern Slovakia, is developed in the Middle Triasic dark-grey Gutenstein limestone of the Biely Va´h Series of the Chocˇ Nappe, by ancient ponor waters of the Biely Va´h side branch. The cave length is 530 m, the entrance/exit is at an altitude of 784 m. Air temperature ranges between 6.5 and 7.1 8C, relative humidity between 94 and 96 %. Radon monitoring in both caves was performed using the Barasol detector (Algade, France) based on alpha particle detection. Impulses were recorded every 10 min. In the Domica cave, three stable monitoring stations equipped with an automatic measuring and registration instruments for continual microclimatic, hydrological and hydrochemical monitoring were installed and operated by the Microstep-MIS company(10). Radon
# The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at Universitaetsbibliothek Giessen on June 15, 2015
I. Smetanova´1,*, K. Holy´2, J. Zelinka3 and J. Omelka4 1 Geophysical Institute, Slovak Academy of Sciences, Du´bravska´ cesta 9, Bratislava 845 28, Slovakia 2 Department of Nuclear Physics and Biophysics, Faculty of Mathematics, Physics and Informatics, Comenius University, Mlynska´ dolina, Bratislava 842 48, Slovakia 3 State Nature Conservancy of the Slovak Republic, Slovak Caves Administration, Hodzˇova 11, Liptovsky´ Mikula´sˇ 031 01, Slovakia 4 ˇ avojske´ho 1, Bratislava 841 04, Slovakia MicroStep-MIS, C
´ ET AL. I. SMETANOVA
seasonal, daily and short-term variations. The character of seasonal variation was different (Figure 1). Seasonal trend in Domica cave was characterised by the highest radon concentration in September and the lowest from February to March. Hourly average of radon activity concentration varied between 90 and 4700 Bq m23. However, values from 500 to 2000 Bq m23 prevailed in the data set (90 %). In the Vazˇecka´ cave, the highest values were registered from June to September 2012 and in January 2013. The hourly average of radon activity concentration varied between 700 and 5800 Bq m23. During the summer months, radon activity concentration was relatively stable, in the rest of the year short-term variations occurred. The character of the short-term variations in both investigated caves was similar; however, they occurred in a different part of a year. Short-term variations were non-periodic, lasting 4–13 d. Using linear regression of radon time series, no connection with atmospheric temperature or atmospheric pressure variations was confirmed. Based on measured radon data and the exact time a cave guide spent in the cave, provided by the cave stuff, the annual effective dose for a cave guide was assessed, using an equilibrium factor for a cave of F ¼ 0.5(12) and a dose conversion factor of 9 nSv (Bq H m23)21(13). The annual effective dose for a guide in the Domica cave is estimated up to 2 mSv. In months with the highest radon activity concentration (July –October), a visitor receives an effective dose of 5.7 mSv during a tour lasting 1 h. In the Vazˇecka´ cave, the annual effective dose for a cave guide is higher, up to 6 mSv. The effective dose received by a visitor in
RESULTS Radon activity concentration in the Vazˇecka´ cave was significantly higher than in Domica. Daily average of radon activity concentration in the Vazˇecka´ cave ranged from 900 to 5300 Bq m23, and in the Domica cave it varied between 500 and 2700 Bq m23. Radon activity concentration in the atmosphere of both the Domica and Vazˇecka´ caves exhibited
Figure 1. Seasonal variation of 222Rn activity concentration (hourly averages) in the Vazˇecka´ and Domica caves.
66
Downloaded from http://rpd.oxfordjournals.org/ at Universitaetsbibliothek Giessen on June 15, 2015
was monitored from June 2010 to July 2011, at the station at the Virgin passage, situated away from the tourist route. Among others, the internal air temperature, CO2 content and wind speed and wind direction were continually monitored there. The meteorological station situated near the cave includes sensors for measuring of air temperature, relative humidity, wind speed, wind direction, global radiation, rainfall amount and evaporation. Atmospheric pressure data were obtained from the meteorological station of Slovak Hydrometeorological Institute in Kosˇice, 80 km NE from the Domica cave. Radon research in the Vazˇecka´ cave started in June 2012 and it is still being carried out. A detector is placed at the most distant place from the entrance, named Gale´ria, which is part of the tourist route. The Gale´ria is the highest as well as the warmest part of the cave(11). The internal air temperature, CO2 content, humidity, wind speed and wind direction are also monitored there. Atmospheric temperature and pressure values were taken from meteorological station operated by the Geophysical Institute of Slovak Academy of Sciences in Stara´ Lesna´, 40 km NE of the Vazˇec village.
TEMPORAL VARIABILITY OF RADON
months with the highest radon activity concentration (June–September) is 7.8 mS during a visit lasting 25 min. Domica cave The internal wind speed measured in the Virgin passage exhibited clear daily variations that documented the changes of air flow in the cave during the day. Wind speed was low, typically ,0.2 m s21, but occasionally reached up to 0.4 m s21(14). The internal air temperature of the cave at the Virgin passage ranged from 9 to 11 8C and it was markedly affected by rainfall(14, 15). In summer months, the air exchange rate between cave environment and outside atmosphere was low. From June to August, relative stable radon values were recorded, mainly in the interval 500 –1500 Bq m23. The influence of air flow on radon values and radon daily variations was not observed. The inside air movement was recorded exclusively after rainfall and it does not affect radon activity concentration values in the cave atmosphere. The daily variations of radon activity concentration in underground environment are most pronounced when the difference between internal air temperature of the cave and atmospheric temperature changed its sign over 24 h. Diurnal radon variations in the Domica cave were observed predominantly in spring and autumn months. The largest amplitudes of daily radon variations up to 2300 Bq m23 were registered from September to October, when air movement was observed mainly from 6 p.m. to 6 a.m. (Figure 2). In this part of the day, the temperature of outside air was lower than inside the cave. Air of lower activity flowed into the cave and radon activity concentration in the Virgin passage decreased due to the natural
Vazˇecka´ cave The former microclimatology research in the Vazˇecka´ cave(11) proved that air masses and environmental conditions at the measuring point Gale´ria are stable. The entrance door is flush fitting and there is no other entrance or crack connecting the cave with the outdoor atmosphere. A weak air flow was registered only when visitors entered the cave; however, no impact on radon variations was found. No air movement was registered during December and January, as well as on Mondays, when the cave was closed to the public. Air movement in January was registered solely in days when paleontological research was performed there.
Figure 2. Diurnal variation of radon, the difference in internal and external air temperatures and wind direction in the Virgin passage in autumn season.
67
Downloaded from http://rpd.oxfordjournals.org/ at Universitaetsbibliothek Giessen on June 15, 2015
ventilation. The measured wind direction was NW, air ˇ ertova was drawn to the Virgin passage from the C diera cave. Contrary, when the difference between internal and atmospheric temperature was negative, the air flowed into the cave stopped and radon activity concentration increased again (Figure 2). In winter months, the outside air temperature was lower than the temperature of cave atmosphere during the whole day (Figure 3). A continual flow of atmospheric air into the cave proceeded permanently and the cave was naturally ventilated. It resulted in a distinct decrease in radon activity concentration in comparison with the rest of the year. From January to March, measured values ranged mostly between 300 and 1100 Bq m23. In days, when the air flow was weak, an immediate increase of radon was observed as a result of radon exhalation from the rock. As the air flow started again, a steep radon decrease was registered (Figure 3).
´ ET AL. I. SMETANOVA
Figure 4. Seasonal variation of radon and the difference in internal and external air temperatures in the Vazˇecka´ cave.
Despite the cave being well isolated from the outside environment, radon activity concentration exhibited significant temporal variations (Figure 4). From April to the end of October, the atmospheric temperature was higher than the temperature of the internal atmosphere. Natural ventilation of the cave was negligible and radon reached high and relatively stable values, hourly averages ranged mainly from 4000 to 5000 Bq m23. From November to March, the temperature of cave atmosphere was higher than the outside air temperature and radon concentration decreased. Low radon level was disturbed by the significant short-term variations, and they appeared when the temperatures of internal and outside air were equal (Figure 4). Several short-term radon increases followed a preceding rainfall event (Figure 5). After a significant rainfall, part of the cave situated close to the Gale´ria was often flooded, because of an increased underground water
level. As the water level in the cracked rock environment rose, it probably pushed radon-rich air from the rock cracks to the cave atmosphere and it could influence radon concentration in cave atmosphere. The largest amplitudes of radon daily variations up to 1000 Bq m23 were registered in summer months. In winter, the daily variations were absent. The seasonal and daily cycles of radon activity concentration seemed to be connected with the atmospheric temperature changes. CONCLUSIONS In both examined caves, a significant temporal variation of 222Rn activity concentration was found, although the Vazˇecka´ cave is well isolated from an outside atmosphere. The character of seasonal variation was different. In the Domica cave, the maximum was registered in 68
Downloaded from http://rpd.oxfordjournals.org/ at Universitaetsbibliothek Giessen on June 15, 2015
Figure 3. Diurnal variation of radon, the difference in internal and external air temperatures and wind direction in the Virgin passage in winter season.
TEMPORAL VARIABILITY OF RADON
September and minimum in February and March, and in the Vazˇecka´ cave, the maximum was observed in summer months and minimum in winter. The seasonal and daily variations of 222Rn activity concentration are assumed to be associated with the atmospheric temperature changes. No effect of atmospheric pressure on radon short-term variation was found. In the Vazˇecka´ cave, some of radon short-term variations may be associated with the rainfall events.
7.
8.
9.
FUNDING This study was supported by Scientific Grant Agency of Ministry of Education of Slovak Republic (VEGA project 2/0135/12).
10.
REFERENCES
11.
1. Duen˜as, C., Ferna´ndez, M. C., Can˜ete, S., Carretero, J. and Liger, E. 222Rn concentrations, natural flow rate and the radiation exposure levels in the Nerja Cave. Atmos. Environ. 33, 501– 510 (1999). 2. Przylibski, T. A. Radon concentration changes in the air of two caves in Poland. J. Environ. Radioact. 45, 81– 94 (1999). 3. Barbosa, S. M., Zafrir, H., Malik, U. and Piatibratova, O. Multi-year to daily radon variability from continuous monitoring at the Amram tunnel, southern Israel. Geophys. J. Int. 182(2), 829– 842 (2010). 4. Perrier, F. and Richon, P. Spatiotemporal variation of radon and carbon dioxide concentrations in an underground quarry: coupled processes of natural ventilation, barometric pumping and internal mixing. J. Environ. Radioact. 101, 279– 296 (2010). 5. Gregoricˇ, A., Zidansˇek, A. and Vaupoticˇ, J. Dependance of radon levels in Postojna Cave on outside air temperature. Nat. Hazards Earth Syst. Sci. 11, 1523–1528 (2011). 6. Whittlestone, S., James, J. and Barnes, C. The relationship between local climate and radon concentrations in
12.
13.
14.
15.
69
the Temple of Baal, Jenolan Caves, Australia. Helictite, 38(2), 39–44 (2003). Lario, J., Sa´nchez-Moral, S., Can˜averas, J. C., Cuezva, S. and Soler, V. Radon continuous monitoring in Altamira Cave (northern Spain) to assess user´s annual effective dose. J. Environ. Radioact. 80, 161–174 (2005). ˇ urcˇ´ık, M. and Nikodemova´, D. Vicˇanova´, M., D Sledovanie vy´skytu rado´nu v podzemny´ch pracovny´ch priestoroc Radon monitoring in underground working places. In: Proceedings of the Conference Ra´dioaktivita v zˇivotnom prostredı´, Spisˇska´ Nova´ Ves, Slovakia, 21– 22 October, pp. 42– 44 (1997) (in Slovak). Briestensky´, M., Thinova´, L., Stemberk, J. and Rowberry, M. D. The use of caves as observatories for recent geodynamic activity and radon gas concentrations in the Western Carpathians and Bohemian Massif. Radiat. Prot. Dosim. 145, 166– 172 (2011). Gazˇ´ık, P., Haviarova´, D. and Zelinka, J. Integrovany´ monitorovacı´ syste´m jasky´nˇ/integrated monitoring system of caves. Aragonit 14/2, 109– 112. (2009) (in Slovak). Zelinka, J. Thermodynamic characteristic of the Vazˇecka´ cave. In: Proceedings of the Conference Vy´skum, vyuzˇ´ıvanie a ochrana jasky´nˇ 3, Stara´ Lesna´, Slovakia, 14– 16 November, pp. 123–131 (2001) (in Slovak). Gillmore, G. K., Phillips, P., Denman, A. J., Sperrin, M. and Pearce, G. radon levels in abandoned metalliferous mines, Devon, Southwest England. Ecotoxicol. Environ. Saf. 49, 2819– 2292 (2000). United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). Sources and effects of ionizing radiation. Report to the General Assembly, with Scientific Annexes. Vol. 1 (New York: UNSCEAR United Nations) (2000). Smetanova´, I., Holy´, K., Zelinka, J., Omelka, J. and Jurcˇa´k, D. Sezo´nna zmena objemovej activity rado´nu v ovzdusˇ´ı jaskyne Domica/seasonal change of radon activity concentration in the air of the Domica cave. Aragonit 17(1– 2), 24–27 (2012) (in Slovak). Zelinka, J. Posu´denie vplyvu prı´rodny´ch a antropoge´nnych faktorov na zmeny mikroklimaticke´ho rezˇimu jaskyne Domica/examination of the influence of antropogenic factors on the microclimatic regime changes in the Domica cave. Aragonit 8, 17–20 (2003) (in Slovak).
Downloaded from http://rpd.oxfordjournals.org/ at Universitaetsbibliothek Giessen on June 15, 2015
Figure 5. Rainfall events and radon short-term variations in the Vazˇecka´ cave.
