Open AccessA spherical falling film gas-liquid equilibrator for rapid and continuous measurements of CO2 and other trace gases
Author(s) -
A. Whitman Miller,
Amanda C. Reynolds,
Mark S. Minton
Publication year - 2019
Publication title -
plos one
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.99
H-Index - 332
ISSN - 1932-6203
DOI - 10.1371/journal.pone.0222303
Subject(s) - trace gas , environmental science , surface water , methane , range (aeronautics) , chemistry , mechanics , hydrology (agriculture) , atmospheric sciences , materials science , environmental engineering , geology , physics , organic chemistry , composite material , geotechnical engineering
Use of gas-liquid equilibrators to measure trace gases such as CO 2 , 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 CO 2 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 CO 2 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 CO 2 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.