Smithsonian Environmental Research Center, Edgewater, Maryland, United States of America.
PLoS One. 2019 Sep 25;14(9):e0222303. doi: 10.1371/journal.pone.0222303. eCollection 2019.
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.
气体-液体平衡器被广泛用于测量水体中的痕量气体，如二氧化碳、甲烷和氡。这些测量对于理解各种水质问题至关重要，例如由于二氧化碳升高导致的酸化，或与生态系统代谢和功能有关的其他过程。然而，由于气体-液体平衡器依赖于产生足够的表面积来促进液相和气相之间的气体交换，大多数传统的平衡器将水通过小的孔口或间隙流过，这些孔口或间隙在高生产力或浑浊的水中会迅速堵塞，这种情况在河口、沿海湾和河流系统中很常见。同样，在低温下，这种平衡器容易结冰。这两种情况都会导致故障，限制其使用，特别是对于长期连续的环境监测。在这里，我们描述并测试了一种气体-液体平衡器，它依赖于水在球形表面上连续的下降薄膜来驱动气体交换。我们的结果表明，这种设计在完全平衡到水相二氧化碳浓度的能力上是准确的，在广泛的气体浓度范围内是有效的，并且响应时间与其他平衡器设计相当。由于这种平衡器使用自由流动的下降水来产生气体交换表面，我们的现场试验表明它非常不易堵塞和冻结，因此非常适合在像河口这样的高生产力水域中进行长期部署，在这些水域中，二氧化碳浓度每小时、每天和季节性波动。当在球形表面上产生时，下降薄膜不会受到倾斜的影响，这种情况在船只、小艇或浮标上很常见。
