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The mystery “Well”: A natural cloud chamber?
Journal of Aerosol Science 81 (2015) 70–74
Contents lists available at ScienceDirect
Journal of Aerosol Science journal homepage: www.elsevier.com/locate/jaerosci
Technical note
The mystery “Well”: A natural cloud chamber? Jan Hovorka a, Robert F. Holub b, Vladimir Zdimal c, Jan Bendl a, Philip K. Hopke b,n a b c
Institute for Environmental Studies, Faculty of Science, Charles University in Prague, Prague, Czech Republic Center for Air Resources Engineering and Science, Clarkson University, Potsdam, NY, USA Institute of Chemical Process Fundamentals AS CR, Prague, Czech Republic
a r t i c l e in f o
abstract
Article history: Received 2 October 2014 Received in revised form 28 November 2014 Accepted 2 December 2014 Available online 11 December 2014
A serendipitous discovery was made of a cistern in the eastern Czech Republic that periodically has water droplets falling on the surface of the water when there is no ambient precipitation occurring. Measurements of temperature, humidity, droplet size and other related parameters have been made to try to understand what is inducing the droplet formation. It appears that this system represents an unintentional cloud chamber. & 2014 Elsevier Ltd. All rights reserved.
Keywords: Underground spaces Aerosol Precipitation Convective flow Thermal cloud chamber
1. Introduction There is an Abbey in Broumov in the Czech Republic (50 1350 12.344″N, 16 1190 59.603″E) with a cistern (Fig. S1) that shows an interesting phenomenon. At times when there is water in the cistern, it is possible to observe water droplets falling onto the surface of the water in spite of the presence of clear skies and no ambient precipitation (Fig. S2 and a Video in the Supplementary material). This interesting aerosol phenomenon was serendipitously discovered upon a visit to the Abbey, seeing the effect, and returning on a number of other occasions and seeing that it still was occurring. Thus, we decided to perform an experimental investigation to characterize the system and to the extent possible, determine what was producing the observed water droplets. Supplementary material related to this article can be found online at http://dx.doi.org/10.1016/j.jaerosci.2014.12.001.
2. Experimental description The cistern is about 19 m deep and approximately 2.4 m in diameter. The observed internal “rain” has been observed on very many occasions when there is standing water in the system and even for some time after all of the water has been absorbed into the ground. The upper walls are brick on which some vegetation has grown (Supplementary Fig. S3). The majority of the cistern was dug into the argillite rock from at least 7 m deep to the bottom. n
Corresponding author. E-mail address: [email protected] (P.K. Hopke).
http://dx.doi.org/10.1016/j.jaerosci.2014.12.001 0021-8502/& 2014 Elsevier Ltd. All rights reserved.
J. Hovorka et al. / Journal of Aerosol Science 81 (2015) 70–74
71
In September 2012, ozone (O3) was measured as a function of depth using 12 m long Teflon tube with a Horiba ozone analyzer (Model APOA-360) with data recorded at 1.5 m increments. The measurements were integrated over 3 min and were corrected for losses (o5%). Carbon dioxide (CO2) was measured at 1 m intervals by lowering a Telaire Model 7001 Carbon Dioxide Monitor into the cistern.
Fig. 1. Depth profile of temperature and relative humidity measured at 50, 80, and 117 cm from the wall.
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J. Hovorka et al. / Journal of Aerosol Science 81 (2015) 70–74
In August 2013, a series of measurements were made to better characterize the conditions in the cistern. Instruments were lowered from the top with measurements made periodically for 90 s at each 0.5 m increment (see Supplementary Fig. S4). Temperature (T) and relative humidity (RH) were measured with a Rotronic HC2-SH (Rotronic AG, Bassersdorf, Switzerland ) The devices were lowered at various distances from the wall: 5, 30, 50, 80, and 117 cm with 3 replicate measurements at 0.50 m.
Fig. 2. Depth profile of ozone and carbon dioxide.
Fig. 3. Depth profile of the particle number concentrations. Top: Measurements made in the morning. Bottom: Measurements made in the evening.
J. Hovorka et al. / Journal of Aerosol Science 81 (2015) 70–74
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Fig. 4. Mean measured size distribution of the water droplets falling near the bottom of the cistern.
Particle number concentrations were measured with a TSI P-Trak (model 8525) and a TSI model 3025A ultrafine CPC (TSI, Inc, Shoreview, MN, USA)) with one series of measurements in the morning and another in the early evening. However, the P-Trak failed during the evening measurements so only the UCPC measurements are available. Both the counters were placed in a thermally insulated box. The box was closed and sealed with tape. Stainless steel inlets protruded about 8 cm from the side of the box. The equipment was cooled with blue ice with a cooling capacity of 90 min. The UCPC air flow was induced through polyethylene tubing (length about 20 m). Drop sizes were measured near the bottom of the cistern using a Thies Laser Precipitation Monitor (Thies Clima, Göttingen, Germany) so that the presence of the instrument would not serve as a condensation sink for the water vapor. 3. Results Figure 1 shows the depth profile for temperature and relative humidity at 50, 80, and 117 cm from the wall, respectively. It can be seen that as the probe moved down, the temperature was substantially reduced and the RH increased to at least 100%. The instrument could not accurately measure the RH at the lower depths since moisture would condense onto the unit. Assuming cylindrical symmetry, we can then develop a contour map of the T and RH profiles in the cistern and they are presented in Supplementary Figs. S5 and S6. It can be seen that by about 12 m into the hole, the relative humidity is 100%. Figure 2 shows the profile of O3 and CO2 as a function of depth. Ozone was clearly entering the system at ground level and was rapidly depleted over the first 3 m. Carbon dioxide behaved very differently showing a sharp increase at 8–10 m deep and holding constant from 9.5 m down to surface of the water. We hypothesize that the CO2 out-gasses from the surrounding soil and the profile shows the clear stratification of the system with the upper portion relatively well mixed down to a depth of approximately 6 m and a transition zone between 6 and 10 m deep. Figure 3 shows the depth profile of the particle counts. The top figure shows measurements made in the morning while the bottom figure shows measurements made in the evening. They are relatively similar with the ambient concentrations around 2000 cm 3 and decreasing as the depth increased about 9 m at which point, the concentrations remained approximately constant. The P-Trak and UCPC values were very comparable suggesting that they were entirely larger, likely accumulation mode particles coming in from the ambient air above the cistern. Figure 4 shows the droplet size distribution measured as close as possible to the water surface at the bottom of the cistern and averaged over 3 different measurement periods. The distributions were quite comparable from measurement to measurement. The droplets have a mean size in the 500–750 mm range so they are relatively large compared to typical cloud droplet (Niu et al., 2010). 4. Discussion and conclusions Our working hypothesis is that this system is achieving a low degree of supersaturation that activates and grows the ambient aerosol particles coming into it from the top into the observed water droplets. There needs to be a steady supply of particles into the nucleation zone given the continuity of the observed droplet production. Thus, it seems likely that there are slow convective cells that develop along the walls down to a depth of the order of 8–9 m where the particle number becomes constant. Since it represents a dynamic system, it cannot be easily modeled as is done with a thermal diffusion cloud chamber (e.g. Bertelsmann and Heist, 1998). It will require complex fluid dynamic modeling that is beyond the scope of this preliminary study.
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J. Hovorka et al. / Journal of Aerosol Science 81 (2015) 70–74
Ambient particulate matter would largely be accumulation mode particles of secondary origins such as has been observed in Prague (Schwarz et al., 2012) and Ostrava, Czech Republic (Pokorná et al., 2015) and these results support the observed coherence in the P-Trak and UCPC measurements. Such particles would readily deliquesce and grow as they encounter the increasing relative humidity since even near the top of the system, the RH exceeds typical deliquescence relative humidity values observed for the ambient aerosol (Koloutso-Vakakis and Rood, 1994; Torkmahalleh et al., 2012). Khlystov et al. (1996) observed that up to 72% (Khairoutdinov and Kogan, 2000) of the ambient particles in Amsterdam could activate as cloud condensation nuclei. As the wet particles reach the supersaturated zone, they then undergo rapid condensational growth into the observed droplet size distribution. Similar growth is observed and modeled in clouds with supersaturations as low as 0.1% (Khairoutdinov and Kogan, 2000). It was obviously thought provoking to observe “rain” in the cistern under clear sky conditions and we believe we have a reasonable explanation for the observed phenomenon and wonder about the existence of other such unusual nucleation and growth systems. Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.jaerosci. 2014.12.001.
References Bertelsmann, A., & Heist, R.H. (1998). Diffusion cloud chamber operation and the background gas effect. Atmospheric Research, 46, 195–209. Khairoutdinov, M., & Kogan, Y. (2000). A new cloud physics parameterization in a large-eddy simulation model of marine stratocumulus. Monthly Weather Review, 128, 229–243. Khlystov, A., Kos, G.P.A., Ten Brink, H.M., Kruisz, C., & Berner, A. (1996). Activation properties of ambient aerosol in the Netherlands. Atmospheric Environment, 30, 3281–3290. Koloutso-Vakakis, S., & Rood, M.J. (1994). The (NH4)2SO4–Na2SO4–H2O system: comparison of deliquescence humidities measured in the field and estimated from laboratory measurements and thermodynamic modeling. Tellus, 46B, 1–15. Niu, S., Jia, X., Sang, J., Liu, X., Lu, C., & Liu, Y. (2010). Distributions of raindrop sizes and fall velocities in a semiarid plateau climate: convective versus stratiform rains. Journal of Applied Meteorology and Climatology, 49, 632–645. Pokorná, P., Hovorka, J., Klán, M., & Hopke., P.K. (2015). Source apportionment of size resolved particulate matter at a European air pollution hot spot. Science of the Total Environment, 502, 172–183. Schwarz, J., Štefancová, L., Maenhaut, W., Smolík, J., & Ždímal, V. (2012). Mass and chemically speciated size distribution of Prague aerosol using an aerosol dryer – the influence of air mass origin. Science of the Total Environment, 437, 348–362. Torkmahalleh, M., Lin, L., Holsen, T.M., Rasmussen, D.H., & Hopke, P.K. (2012). The impact of deliquescence and pH on chromium speciation in ambient PM. Aerosol Science and Technology, 46(6), 690–696.
Contents lists available at ScienceDirect
Journal of Aerosol Science journal homepage: www.elsevier.com/locate/jaerosci
Technical note
The mystery “Well”: A natural cloud chamber? Jan Hovorka a, Robert F. Holub b, Vladimir Zdimal c, Jan Bendl a, Philip K. Hopke b,n a b c
Institute for Environmental Studies, Faculty of Science, Charles University in Prague, Prague, Czech Republic Center for Air Resources Engineering and Science, Clarkson University, Potsdam, NY, USA Institute of Chemical Process Fundamentals AS CR, Prague, Czech Republic
a r t i c l e in f o
abstract
Article history: Received 2 October 2014 Received in revised form 28 November 2014 Accepted 2 December 2014 Available online 11 December 2014
A serendipitous discovery was made of a cistern in the eastern Czech Republic that periodically has water droplets falling on the surface of the water when there is no ambient precipitation occurring. Measurements of temperature, humidity, droplet size and other related parameters have been made to try to understand what is inducing the droplet formation. It appears that this system represents an unintentional cloud chamber. & 2014 Elsevier Ltd. All rights reserved.
Keywords: Underground spaces Aerosol Precipitation Convective flow Thermal cloud chamber
1. Introduction There is an Abbey in Broumov in the Czech Republic (50 1350 12.344″N, 16 1190 59.603″E) with a cistern (Fig. S1) that shows an interesting phenomenon. At times when there is water in the cistern, it is possible to observe water droplets falling onto the surface of the water in spite of the presence of clear skies and no ambient precipitation (Fig. S2 and a Video in the Supplementary material). This interesting aerosol phenomenon was serendipitously discovered upon a visit to the Abbey, seeing the effect, and returning on a number of other occasions and seeing that it still was occurring. Thus, we decided to perform an experimental investigation to characterize the system and to the extent possible, determine what was producing the observed water droplets. Supplementary material related to this article can be found online at http://dx.doi.org/10.1016/j.jaerosci.2014.12.001.
2. Experimental description The cistern is about 19 m deep and approximately 2.4 m in diameter. The observed internal “rain” has been observed on very many occasions when there is standing water in the system and even for some time after all of the water has been absorbed into the ground. The upper walls are brick on which some vegetation has grown (Supplementary Fig. S3). The majority of the cistern was dug into the argillite rock from at least 7 m deep to the bottom. n
Corresponding author. E-mail address: [email protected] (P.K. Hopke).
http://dx.doi.org/10.1016/j.jaerosci.2014.12.001 0021-8502/& 2014 Elsevier Ltd. All rights reserved.
J. Hovorka et al. / Journal of Aerosol Science 81 (2015) 70–74
71
In September 2012, ozone (O3) was measured as a function of depth using 12 m long Teflon tube with a Horiba ozone analyzer (Model APOA-360) with data recorded at 1.5 m increments. The measurements were integrated over 3 min and were corrected for losses (o5%). Carbon dioxide (CO2) was measured at 1 m intervals by lowering a Telaire Model 7001 Carbon Dioxide Monitor into the cistern.
Fig. 1. Depth profile of temperature and relative humidity measured at 50, 80, and 117 cm from the wall.
72
J. Hovorka et al. / Journal of Aerosol Science 81 (2015) 70–74
In August 2013, a series of measurements were made to better characterize the conditions in the cistern. Instruments were lowered from the top with measurements made periodically for 90 s at each 0.5 m increment (see Supplementary Fig. S4). Temperature (T) and relative humidity (RH) were measured with a Rotronic HC2-SH (Rotronic AG, Bassersdorf, Switzerland ) The devices were lowered at various distances from the wall: 5, 30, 50, 80, and 117 cm with 3 replicate measurements at 0.50 m.
Fig. 2. Depth profile of ozone and carbon dioxide.
Fig. 3. Depth profile of the particle number concentrations. Top: Measurements made in the morning. Bottom: Measurements made in the evening.
J. Hovorka et al. / Journal of Aerosol Science 81 (2015) 70–74
73
Fig. 4. Mean measured size distribution of the water droplets falling near the bottom of the cistern.
Particle number concentrations were measured with a TSI P-Trak (model 8525) and a TSI model 3025A ultrafine CPC (TSI, Inc, Shoreview, MN, USA)) with one series of measurements in the morning and another in the early evening. However, the P-Trak failed during the evening measurements so only the UCPC measurements are available. Both the counters were placed in a thermally insulated box. The box was closed and sealed with tape. Stainless steel inlets protruded about 8 cm from the side of the box. The equipment was cooled with blue ice with a cooling capacity of 90 min. The UCPC air flow was induced through polyethylene tubing (length about 20 m). Drop sizes were measured near the bottom of the cistern using a Thies Laser Precipitation Monitor (Thies Clima, Göttingen, Germany) so that the presence of the instrument would not serve as a condensation sink for the water vapor. 3. Results Figure 1 shows the depth profile for temperature and relative humidity at 50, 80, and 117 cm from the wall, respectively. It can be seen that as the probe moved down, the temperature was substantially reduced and the RH increased to at least 100%. The instrument could not accurately measure the RH at the lower depths since moisture would condense onto the unit. Assuming cylindrical symmetry, we can then develop a contour map of the T and RH profiles in the cistern and they are presented in Supplementary Figs. S5 and S6. It can be seen that by about 12 m into the hole, the relative humidity is 100%. Figure 2 shows the profile of O3 and CO2 as a function of depth. Ozone was clearly entering the system at ground level and was rapidly depleted over the first 3 m. Carbon dioxide behaved very differently showing a sharp increase at 8–10 m deep and holding constant from 9.5 m down to surface of the water. We hypothesize that the CO2 out-gasses from the surrounding soil and the profile shows the clear stratification of the system with the upper portion relatively well mixed down to a depth of approximately 6 m and a transition zone between 6 and 10 m deep. Figure 3 shows the depth profile of the particle counts. The top figure shows measurements made in the morning while the bottom figure shows measurements made in the evening. They are relatively similar with the ambient concentrations around 2000 cm 3 and decreasing as the depth increased about 9 m at which point, the concentrations remained approximately constant. The P-Trak and UCPC values were very comparable suggesting that they were entirely larger, likely accumulation mode particles coming in from the ambient air above the cistern. Figure 4 shows the droplet size distribution measured as close as possible to the water surface at the bottom of the cistern and averaged over 3 different measurement periods. The distributions were quite comparable from measurement to measurement. The droplets have a mean size in the 500–750 mm range so they are relatively large compared to typical cloud droplet (Niu et al., 2010). 4. Discussion and conclusions Our working hypothesis is that this system is achieving a low degree of supersaturation that activates and grows the ambient aerosol particles coming into it from the top into the observed water droplets. There needs to be a steady supply of particles into the nucleation zone given the continuity of the observed droplet production. Thus, it seems likely that there are slow convective cells that develop along the walls down to a depth of the order of 8–9 m where the particle number becomes constant. Since it represents a dynamic system, it cannot be easily modeled as is done with a thermal diffusion cloud chamber (e.g. Bertelsmann and Heist, 1998). It will require complex fluid dynamic modeling that is beyond the scope of this preliminary study.
74
J. Hovorka et al. / Journal of Aerosol Science 81 (2015) 70–74
Ambient particulate matter would largely be accumulation mode particles of secondary origins such as has been observed in Prague (Schwarz et al., 2012) and Ostrava, Czech Republic (Pokorná et al., 2015) and these results support the observed coherence in the P-Trak and UCPC measurements. Such particles would readily deliquesce and grow as they encounter the increasing relative humidity since even near the top of the system, the RH exceeds typical deliquescence relative humidity values observed for the ambient aerosol (Koloutso-Vakakis and Rood, 1994; Torkmahalleh et al., 2012). Khlystov et al. (1996) observed that up to 72% (Khairoutdinov and Kogan, 2000) of the ambient particles in Amsterdam could activate as cloud condensation nuclei. As the wet particles reach the supersaturated zone, they then undergo rapid condensational growth into the observed droplet size distribution. Similar growth is observed and modeled in clouds with supersaturations as low as 0.1% (Khairoutdinov and Kogan, 2000). It was obviously thought provoking to observe “rain” in the cistern under clear sky conditions and we believe we have a reasonable explanation for the observed phenomenon and wonder about the existence of other such unusual nucleation and growth systems. Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.jaerosci. 2014.12.001.
References Bertelsmann, A., & Heist, R.H. (1998). Diffusion cloud chamber operation and the background gas effect. Atmospheric Research, 46, 195–209. Khairoutdinov, M., & Kogan, Y. (2000). A new cloud physics parameterization in a large-eddy simulation model of marine stratocumulus. Monthly Weather Review, 128, 229–243. Khlystov, A., Kos, G.P.A., Ten Brink, H.M., Kruisz, C., & Berner, A. (1996). Activation properties of ambient aerosol in the Netherlands. Atmospheric Environment, 30, 3281–3290. Koloutso-Vakakis, S., & Rood, M.J. (1994). The (NH4)2SO4–Na2SO4–H2O system: comparison of deliquescence humidities measured in the field and estimated from laboratory measurements and thermodynamic modeling. Tellus, 46B, 1–15. Niu, S., Jia, X., Sang, J., Liu, X., Lu, C., & Liu, Y. (2010). Distributions of raindrop sizes and fall velocities in a semiarid plateau climate: convective versus stratiform rains. Journal of Applied Meteorology and Climatology, 49, 632–645. Pokorná, P., Hovorka, J., Klán, M., & Hopke., P.K. (2015). Source apportionment of size resolved particulate matter at a European air pollution hot spot. Science of the Total Environment, 502, 172–183. Schwarz, J., Štefancová, L., Maenhaut, W., Smolík, J., & Ždímal, V. (2012). Mass and chemically speciated size distribution of Prague aerosol using an aerosol dryer – the influence of air mass origin. Science of the Total Environment, 437, 348–362. Torkmahalleh, M., Lin, L., Holsen, T.M., Rasmussen, D.H., & Hopke, P.K. (2012). The impact of deliquescence and pH on chromium speciation in ambient PM. Aerosol Science and Technology, 46(6), 690–696.