بررسی تجربی تأثیر ذرات آب‌دوست بر تعدیل مه

نویسندگان

1 دانشجوی کارشناسی ارشد، گروه فیزیک فضا، مؤسسه ژئوفیزیک، دانشگاه تهران، تهران، ایران

2 استاد، گروه فیزیک فضا، مؤسسه ژئوفیزیک، دانشگاه تهران، تهران، ایران

3 استادیار، گروه فیزیک فضا، مؤسسه ژئوفیزیک، دانشگاه تهران، تهران، ایران

4 دانشجوی کارشناسی ارشد، دانشکده ریاضی، آمار و علوم کامپیوتر، دانشگاه تهران، تهران، ایران

چکیده

تشکیل مه باعث کم شدن دید افقی می­شود و دید افقی پایین می­تواند باعث بروز مشکلاتی عمدتاً در فرودگاه­ها و جاده‌ها شود. از این­رو با تشکیل مه مصنوعی در آزمایشگاه، تأثیر برخی هواویزها بر روی مه بررسی می­شود. ذرات آب­دوست می­توانند به‌عنوان هسته­های میعان با افزایش شعاع مؤثر و کاهش غلظت قطرک­ها، در تعدیل مه مؤثر باشند. در این مطالعه، آزمایش­ها بر روی سدیم هیدروکسید، اوره و نمک انجام شده است که با هواویزهای زمینه مقایسه شده­اند. ابتدا عمق نوری مه محاسبه و سپس توزیع اندازه قطرک­های مه تخمین زده می­شود. همچنین دیگر پارامترها مانند غلظت قطرک­های مه، محتوای آب مایع و زمان ماندگاری مه، مورد ارزیابی قرار می­گیرد. نتایج حاکی از آن است که ذرات آب­دوست به‌عنوان هسته­های میعان، نقش به‌سزایی را در تعدیل مه ایفا می­کنند. به­طوری‌که در حضور این ذرات، غلظت قطرک­های مه در مقایسه با هواویزهای زمینه کاهش یافته است و مه رقیق­تر شده است. در حضور ذرات سدیم هیدروکسید غلظت کل قطرک­ها کاهش زیادی داشته است و مدت‌زمان ماندگاری مه به 31 ثانیه رسیده است که نشان می­دهد این ترکیب برای تعدیل مه عملکرد بهتری داشته است. همچنین هنگامی‌که ذرات سدیم هیدروکسید درون محفظه وجود داشتند، به‌طور مشاهداتی قطرک­های بسیار کوچکی که در انتهای فرآیند سه آزمایش دیگر بر روی پرتوی لیزر نوسان می­کردند، برای این ذرات وجود نداشتند.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Experimental study of the effect of hydrophilic particles on fog modification

نویسندگان [English]

  • Amir Bagheri Mosleh-Abadi 1
  • Abbas Ali Aliakbari-Bidokhti 2
  • Maryam Gharaylou 3
  • Reza Khalife 4
1 M.Sc. Student, Department of Space Physics, Institute of Geophysics, University of Tehran, Tehran, Iran
2 Professor, Department of Space Physics, Institute of Geophysics, University of Tehran, Tehran, Iran
3 Assistant Professor, Department of Space Physics, Institute of Geophysics, University of Tehran, Tehran, Iran
4 M.Sc. Student, Department of Statistics, Faculty of mathematics, statistics & computer Science, University of Tehran, Tehran, Iran
چکیده [English]

Fog formation reduces the visibility, and low visibility cause problems mainly in airports and roads. Fog modification or even clearance can reduce such problems. Here, in the laboratory the effects of some aerosols on the modification of artificial fog have been investigated. This research is carried out using the method used in the work of Vajaiac et al. (2014), for hydrophilic particles. These particles, as the fog modification factor, can be effective as condensation nuclei by increasing the effective radius of the droplets and reducing the concentrations of the fog droplets in the fog.. We used a glass chamber with a height of 41cm and diameter of 28 cm in which a red laser and a detector were placed on both sides of the chamber. We dissolved water-soluble compounds in water and by pumping the air into water of the chamber, the bubbles are formed and their breaking led to formation of particles. Then the particles are dispersed inside the chamber, while the pressure inside the chamber was increased with an air pump, and so the temperature was rised. Then suddenly or quasi-adiabaticaly, the pressure is released and hence, the air temperature was dropped creating the fog (cloud). The cloud droplets are mainly formed on these particles. With the formation of droplets, the received laser signal was decreased and after falling all of droplets, the received laser signal reached its primary level. Hence, by measuring the level of drop in the signal and its duration some properties to the cloud structure can be found.
In this study, we used sodium hydroxide, urea, and salt particles that was compared with background aerosols affecting the cloud. First, the optical depth of fog was calculated and then size distribution of fog droplets was estimated. Also other parameters like the concentration of the fog droplets, liquid water content and fog lifetime were evaluated. The results show that hydrophilic particles as condensation nuclei played a significant role in fog modification. So, in the presence of these particles, the concentration of fog droplets in comparison with that of the background aerosols, was decreased and the fog was diluted significantly. The maximum of fog lifetime was observed in the presence of background aerosols as 63 s, also these particles have had the lowest effective radius of 7.77µm. In the presence of sodium hydroxide particles, the concentration of total droplets was decreased significantly. In addition, the maximum effective radius was 10.48 µm for these particles. Also, fog lifetime was reduced to 31s which suggests that this component for fog modification has a better performance. The area under the curve’s of the size distribution of droplets for salt and urea were nearly identical, that indicated the concentration of the droplets was close to each other. Parasitic structures might appear in curves of the size distribution of droplets that were smoothed. As the time passed all of the effective radius curves showed decreasing trends due to the fact that, the larger droplets can droped out of the laser beam, so gradually the effective radius should be decreased. In comparison with other compounds, when sodium hydroxide particles were used in the cloud chamber, observationally small droplets that moved up an down in the laser beam weren’t present, hence no oscillations were seen in the laser signal. Considering experimental errors, while neglecting the process of coalescence that might occur in the falling stage of the droplets, when the droplets were passing the laser beam, they appeared at larger sizes, which could lead to an overestimation. The signal noises and non-uniform distribution of condensation nuclei could also be considered as experimental errors.

کلیدواژه‌ها [English]

  • Hydrophilic particles
  • Experimental study
  • Droplets
  • Fog modification

باقری مصلح­آبادی، ا.، علی‌اکبری بیدختی، ع. ع.، قرایلو، م. و خلیفه، ر.، 1397، مطالعه آزمایشگاهی تخمین توزیع اندازه قطرک­های ابر در حضور هواویز دوده، هجدهمین کنفرانس ژئوفیزیک ایران.

شوشتری، م. ح.، ناجی، ف. و علی‌اکبری بیدختی، ع. ع.، 1392، بررسی آزمایشگاهی نقش یون­ها در تشکیل ابر گرم، م. فیزیک زمین و فضا، 39(4)، 123-134.

صادقی حسینی، س. ع. و ارکیان، ف.، 1380، بررسی آزمایشگاهی بارورسازی ابرهای گرم، م. فیزیک زمین و فضا، 27(2)، 15-23.

فهندژ سعدی، ح.، علی‌اکبری بیدختی، ع. ع.، قرایلو، م. و شوشتری، م. ح. 1394، مطالعه تجربی نقش مواد سطح فعال بر تشکیل ابر گرم در آزمایشگاه، ن. پژوهش­های اقلیم شناسی، (6)، 23 و 24.

Alexandrov, M. D., Cairns, B., Emde, C., Ackerman, A. S. and van Diedenhoven, B., 2012, Accuracy assessments of cloud droplet size retrievals from polarized reflectance measurements by the research scanning polarimeter. Remote sensing of environment, 125, 92-111.

Cermak, J. and Bendix, J., 2011, Detecting ground fog from space–a microphysics-based approach. International Journal of Remote Sensing, 32(12), 3345-3371.

Fountoukis, C., Nenes, A., Meskhidze, N., Bahreini, R., Conant, W. C., Jonsson, H. and Flagan, R. C., 2007, Aerosol–cloud drop concentration closure for clouds sampled during the International Consortium for Atmospheric Research on Transport and Transformation 2004 campaign. Journal of Geophysical Research: Atmospheres, 112(D10).

Gultepe, I., Isaac, G. A. and Strawbridge, K. B., 2001, Variability of cloud microphysical and optical parameters obtained from aircraft and satellite remote sensing measurements during RACE. International journal of climatology, 21(4), 507-525.

Gultepe, I., Müller, M. D. and Boybeyi, Z., 2006, A new visibility parameterization for warm-fog applications in numerical weather prediction models. Journal of applied meteorology and climatology, 45(11), 1469-1480.

Gultepe, I. and Milbrandt, J. A., 2007, Microphysical observations and mesoscale model simulation of a warm fog case during FRAM project. Fog and Boundary Layer Clouds: Fog Visibility and Forecasting, 1161-1178.

Gultepe, I., Hansen, B., Cober, S. G., Pearson, G., Milbrandt, J. A., Platnick, S. and Oakley, J. P., 2009, The fog remote sensing and modeling field project. Bulletin of the American Meteorological Society, 90(3), 341-359.

Huan. L., Baolin. J., Fangzhou. L. and Wenshi., L., 2018, Simulation of the effects of sea-salt aerosols on the structure and precipitation of a developed tropical cyclone, Journal of Atmospheric Research, Accepted.

Houghton, H. G. and Radford, W. H., 1938, On the local dissipation of natural fog. Massachusetts Institute of Technology and Woods Hole Oceanographic Institution.

Jiusto, J. E., Pilie, R. J. and Kocmond, W. C., 1968, Fog modification with giant hygroscopic nuclei. Journal of Applied Meteorology and applied meteorology, 7(5), 860-869.

Kunkel, B. A., 1984, Parameterization of droplet terminal velocity and extinction coefficient in fog models. Journal of Climate and applied meteorology, 23(1), 34-41.

Liou, K. N., 2002, An Introduction to Atmospheric Radiation, Second Edition Academic Press, Amsterdam.

Moradi, S., Bidokhti, A. A., Gharaylou, M., Jalaie, S. and Shoushtari, M. H., 2014, Study of the Effects of Acidic Ions on Cloud Droplet Formation Using Laboratory Experiments. APCBEE procedia, 10, 246-250.

Pinsky, M., Khain, A., Mazin, I. and Korolev, A., 2012, Analytical estimation of droplet concentration at cloud base. Journal of Geophysical Research: Atmospheres, 117(D18).

Ramirez-Beltran, N. D., Kuligowski, R. J., Cardona, M. J. and Cruz-Pol, S. 2009, Warm rainy clouds and droplet size distribution. WSEAS Transaction on Systems, 8(1), 75-85.

Silverman, B. A. and Kunkel, B. A., 1970, A numerical model of warm fog dissipation by hygroscopic particle seeding. Journal of Applied Meteorology, 9(4), 627-633.

Vâjâiac, S. N., Filip, V., Ștefan, S. and Boscornea, A., 2014, Assessing the size distribution of droplets in a cloud chamber from light extinction data during a transient regime. Journal of Atmospheric and Solar-Terrestrial Physics, 109, 29-36.

Zhang, J., Xue, H., Deng, Z., Ma, N., Zhao, C. and Zhang, Q., 2014, A comparison of the parameterization schemes of fog visibility using the in-situ measurements in the North China Plain. Atmospheric environment, 92, 44-50.