A spherical falling film gas-liquid equilibrator for rapid and continuous measurements of CO2 and other trace gases

Autoři: A. Whitman Miller aff001;  Amanda C. Reynolds aff001;  Mark S. Minton aff001
Působiště autorů: Smithsonian Environmental Research Center, Edgewater, Maryland, United States of America aff001
Vyšlo v časopise: PLoS ONE 14(9)
Kategorie: Research Article
doi: 10.1371/journal.pone.0222303


Use of gas-liquid equilibrators to measure trace gases such as CO2, methane, and radon in water bodies is widespread. Such measurements are critical for understanding a variety of water quality issues such as acidification due to elevated CO2 or other processes related ecosystem metabolism and function. However, because gas-liquid equilibrators rely on generating sufficient surface area for gas exchange between liquid and gas phases, most traditional equilibrators pass water through small orifices or interstitial spaces that rapidly clog in highly productive or turbid waters, conditions that are common in estuaries, coastal bays, and riverine systems. Likewise, in cold temperatures, such equilibrators are subject to freezing. Both situations lead to failure and limit utility, especially for long term, continuous environmental monitoring. Here we describe and test a gas-liquid equilibrator that relies on a continuous falling film of water over a spherical surface to drive gas exchange. Our results demonstrate that this design is accurate in its ability to equilibrate fully to aqueous CO2 concentrations, is functional across a wide range of gas concentrations, and has a response time that is comparable with other equilibrator designs. Because this equilibrator uses free flowing, falling water to produce a surface for gas exchange, our field trials have shown it to be very resistant to clogging and freezing, and therefore well suited to long term deployment in highly productive waters like estuaries where CO2 concentrations fluctuate hourly, daily, and seasonally. When generated across a spherical surface, the falling film is not adversely affected by tilting off vertical, conditions that are common on a ship, small vessel, or buoy.

Klíčová slova:

Carbon dioxide – Flow rate – Fluid flow – Surface water – Thin films – Air flow – Gases – Laminar flow


1. Yoon TK, Jin H, Oh NH, Park JH. Technical note: Assessing gas equilibration systems for continuous pCO2 measurements in inland waters. Biogeosciences. 2016;13(13): 3915–3930.

2. Santos IR, Maher DT, Eyre BD. Coupling automated radon and carbon dioxide measurements in coastal waters. Environ Sci Technol. 2012;46: 7685–7691. doi: 10.1021/es301961b 22694256

3. Cai W-J, Wang Y. The chemistry, fluxes, and sources of carbon dioxide in the estuarine waters of the Satilla and Altamaha Rivers, Georgia. Limnol Oceanogr. 1998;43: 657–668.

4. Salisbury JE, Vandemark D, Hunt CW, Campbell JW, McGillis WR, McDowell WH. Seasonal observations of surface waters in two Gulf of Maine estuary-plume systems: Relationships between watershed attributes, optical measurements and surface pCO2. Estuar Coast. Shelf. S. 2008;77: 245–252.

5. Borges AV, Abril G. Carbon dioxide and methane dynamics in estuaries, In: Wolanski E, McLusky D, editors. Treatise on estuarine and coastal science. Waltham: Academic Press; 2011. pp119–161.

6. Cai WJ. Estuarine and coastal ocean carbon paradox: CO2 sinks or sites of terrestrial carbon incineration? Annu Rev Mar Sci. 2001;3: 123–145.

7. Chen CTA, Huang TH, Chen YC, Bai Y, He X, Kang Y. Air–sea exchanges of CO2 in the world’s coastal seas. Biogeosciences. 2013;10(10): 6509–6544.

8. Abril G, Martinez JM, Artigas LF, Moreira-Turcq P, Benedetti MF, Vidal L, et al. Amazon River carbon dioxide outgassing fueled by wetlands. Nature. 2014;505: 395–398. doi: 10.1038/nature12797 24336199

9. Frankignoulle M, Borges A, Biondo R. A new design of equilibrator to monitor carbon dioxide in highly dynamic and turbid environments. Water Res. 2001;5: 1344–1347.

10. Abril G, Richard S, Guérin F. In situ measurements of dissolved gases (CO2 and CH4) in a wide range of concentrations in a tropical reservoir using an equilibrator. Sci Total Environ. 2006;354(2–3): 246–251. doi: 10.1016/j.scitotenv.2004.12.051 16398998

11. Joesoef A, Huang WJ, Gao Y, Cai WJ. Air–water fluxes and sources of carbon dioxide in the Delaware Estuary: spatial and seasonal variability. Biogeosciences. 2015;12(20): 6085.

12. Lowe AT, Bos J, Ruesink J. Ecosystem metabolism drives pH variability and modulates long-term ocean acidification in the Northeast Pacific coastal ocean. Sci Rep. 2019; 9(1):963. doi: 10.1038/s41598-018-37764-4 30700764

13. Webb JR, Maher DT, Santos IR. Automated, in situ measurements of dissolved CO2, CH4, and δ13C values using cavity enhanced laser absorption spectrometry: Comparing response times of air-water equilibrators. Limnol Oceanogr Methods. 2016;14(5): 323–337.

14. Körtzinger A. Determination of partial pressure of carbon dioxide ((pCO2)). In: Grasshoff K, Kremling K, Ehrhardt M, editors. Methods of seawater analysis. New York: John Wiley & Sons; 2009. pp. 149–158.

15. Johnson JE. Evaluation of a seawater equilibrator for shipboard analysis of dissolved oceanic trace gases. Anal Chim Acta. 1999;395: 119–132. doi: 10.1016/S0003-2670(99)00361-X

16. Sabine CL, Key RM. Surface Water and Atmospheric Underway Carbon Data Obtained During the World Ocean Circulation Experiment Indian Ocean Survey Cruises (R/V Knorr, December 1994 -January 1996) [Internet]. Oak Ridge National Laboratory; 1997. Available from: http://cdiac.ornl.gov/oceans/ndp_064/ndp064.html. Cited 30 Jan 2019.

17. Poisson A, Metzl N, Brunet C, Schauer B, Bres B, Ruiz-Pino D, et al. Variability of sources and sinks of CO2 in the western Indian and southern oceans during the year 1991. J Geophys Res. 1993;98(C12): 22759.

18. Zhang X, Meng C, Qiu Q, Quan S, Shen S. A numerical investigation of liquid film flow and film thickness distribution outside a horizontal tube. IJLCT. 2018;13(4): 424–31.

19. Hassan IA, Sadikin A, Isa NM. The Computational Modeling of Falling Film Thickness Flowing Over Evaporator Tubes. J Adv Res Fluid Mech Therm Sci. 2015;14(1): 14.

20. Ribatski G, Jacobi AM. Falling-film evaporation on horizontal tubes—a critical review. Int J Refrig. 2005;28(5): 635–653.

21. Takagi D, Huppert HE. Flow and instability of thin films on a cylinder and sphere. J Fluid Mech. 2010;647: 221.

22. Nusselt W. Die oberflächenkondensation des wasserdampfes. Zeitschrift des Vereines Deutscher Ingenieure 1916;60(27): 541–546.

23. Nusselt W. Die oberflächenkondensation des wasserdampfes. Zeitschrift des Vereines Deutscher Ingenieure 1916; 60(28): 569–575.

24. Wang X, Fan H, He M, Zhang Y. Measurement of falling film thickness around a horizontal tube using laser-induced fluorescence technique. J Phys Conf Ser. 2009;147: 012039.

25. Kumar A. Numerical Study of Falling Film Thickness on Horizontal Circular Tube—A CFD Approach. Int J Adv Technol. [Internet]. 2016;07(04): doi: 10.4172/0976-4860.1000169

26. Awad MM, Negeed E-SR. Enhancement of evaporation of falling liquid film on horizontal tube bundle. Proceedings of the International Water Technology Conference, IWTC12 2008; Alexandria, Egypt: 1:30.

27. Senseair.com [Internet]. K30 3% Specifications. Available from: https://senseair.com/products/flexibility-counts/senseair-k30-3/. Cited 01 Feb 2019.

28. Licor.com [Internet]. LI-7000 Specifications. Available from: https://www.licor.com/env/products/gas_analysis/LI-7000/specifications.html. Cited 01 Feb 2019.

29. Martin CR, Zeng N, Karion A, Dickerson RR, Ren X, Turpie BN, et al. Evaluation and environmental correction of ambient CO2 measurements from a low-cost NDIR sensor. Atmos Meas Tech. 2017;10(7): 2383–2395.

30. Gülzow W, Rehder G, Schneider B, Deimling JS v, Sadkowiak B. A new method for continuous measurement of methane and carbon dioxide in surface waters using off-axis integrated cavity output spectroscopy (ICOS): An example from the Baltic Sea. Limnol Oceanogr Methods. 2011;9(5): 176–184.

31. Wang ZA, Kroeger KD, Ganju NK, Gonneea ME, Chu SN. Intertidal salt marshes as an important source of inorganic carbon to the coastal ocean: Marsh lateral export of inorganic carbon. Limnol Oceanogr. 2016;61(5): 1916–1931.

32. Jafar F, Thorpe G, Turan OF. Liquid Film Falling on Horizontal Circular Cylinders. 16th Australasian Fluid Mechanics Conference 2007 Dec 2–7; Gold Coast, Australia: 1193–2000.

33. Mudawar I, Houpt RA. Mass and momentum transport in smooth falling liquid films laminarized at relatively high Reynolds numbers. Int J Heat Mass Transf. 1993;36(14): 3437–3448.

34. Brumfield LK, Theofanous TG. On the prediction of heat transfer across turbulent liquid films. J Heat Transfer 1976;98: 496–502.

35. Carey VP. Liquid–vapor phase change phenomena: An introduction to the thermophysics of vaporization and condensation processes in heat transfer equipment. 1st ed. New York: Taylor and Francis Books Ltd; 1992.

36. Roberson JA, Cassidy JJ, Chaudhry MH. Hydraulic engineering. Boston: Houghton Mifflin Company; 1988.

37. Körtzinger A, Thomas H, Schneider B, Gronau N, Mintrop L, Duinker JC. 1996. At-sea intercomparison of two newly designed underway pCO2 system—encouraging results. Mar Chem. 1996;52: 133–145. doi: 10.1016/0304–4203(95)00083-6

38. Crawford JT, Loken LC, Casson NJ, Smith C, Stone AG, Winslow LA. High-speed limnology: Using advanced sensors to investigate spatial variability in biogeochemistry and hydrology. Environ Sci Technol. 2015;49: 442–450. doi: 10.1021/es504773x 25406073

39. Friedrichs G, Bock J, Temps F, Fietzek P, Körtzinger A, Wallace DW. 2010. Toward continuous monitoring of seawater 13CO2/12CO2 isotope ratio of pCO2: Performance of cavity ringdown spectroscopy and gas matrix effects. Limnol Oceanogr Methods. 2010;8: 539–551. doi: 10.4319/lom.2010.8.539

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