A laser based sensor for in situ, real time measurement of dissolved gas: application to CO2 in water

我们提议开发一种仪器概念，以便首次能够以良好的分辨率、在紧凑和可展开的组件中就地、实时地测量溶解在水中的气体。目前对溶解在水中的二氧化碳的测量技术通常涉及将溶解在水中的二氧化碳的量与一定体积的气体中的二氧化碳的量相平衡，然后对气体中的二氧化碳进行光学测量；或者与半透膜后面的电解液进行平衡，并测量所产生的液体的酸度。这两个过程都不是特别快，前者不适合沉浸在海洋中。平衡是一个相对缓慢的过程。因此，很难以高的空间或时间分辨率测量海洋中的二氧化碳剖面。我们建议开发一些创新的基于激光的方法来监测溶解在液体中的气体。第一个目标是将二氧化碳溶解在海水中。利用所提出的方法，不需要平衡，并且应该可以实时(几秒或更好)实现良好的精度。该测量原则上容许污垢，并应对一些主要仪器和环境参数不敏感。该项目的主要任务将包括激光传感器的初步设计和权衡、组装和初步表征、调制方案的开发和定量数据处理，以及验证该技术的最终实验室测试。一个完全开发的仪器将是紧凑的，具有中等的功率要求，可以浸入到相当深的地方，并且应该与船舶进水口、CTD(电导率、温度和深度)玫瑰花状水样和其他海洋剖面仪兼容。拟议的传感器将通过能够对二氧化碳进行三维测量，对地球碳循环的整体研究做出重大贡献。更具体的研究领域包括碳化学和表层二氧化碳通量研究，海洋生物圈和海洋之间的二氧化碳交换，海洋二氧化碳循环，以及评估洋脊和海底火山的二氧化碳渗漏，以了解进入海洋的深层碳路径。良好的空间和时间采样，包括深度采样，也可能适用于小规模或动态二氧化碳分布的研究，用于验证二氧化碳封存实验和监测石油钻探作业。虽然我们将展示我们关于二氧化碳的技术，但传感器概念广泛适用于对任何溶解在液体中的分子物种的传感。因此，其他大量的应用将被解锁，例如应用于水质研究，或液体污染的工业特征。

We propose the development of an instrument concept anticipated to enable for the first time the measurement of gases dissolved in water in-situ, in real time, at good resolution and in a compact and deployable package. Current measurement techniques for CO2 dissolved in water typically involve the equilibration of the amount of CO2 dissolved in water with that in a volume of gas, followed by an optical measurement of the CO2 in the gas; or equilibration with an electrolyte behind a semi-permeable membrane and a measurement of the acidity of the resulting liquid. Neither process is especially fast and the former is not suited to immersion in the ocean. Equilibration is a relatively slow process. Consequently it is difficult to measure oceanic CO2 profiles with high spatial or temporal resolution.We propose to develop some innovative laser-based methods to monitor gases dissolved in liquids. The first application targeted is dissolved CO2 in ocean water. With the proposed approach, no equilibration is required and good precision should be achievable in real time (seconds or better). The measurement is in principle tolerant of fouling and should be insensitive to a number of major instrumental and environmental parameters. The main tasks on the project will include initial design and trade-offs of the laser sensors, assembly and initial characterization, development of modulation schemes and quantitative data processing, and final laboratory tests to validate the technology. A fully developed instrument would be compact, have moderate power requirements, be immersible to significant depths and should be compatible with ship inlets, CTD (conductivity, temperature and depth) rosette water samplers and other ocean profilers.The proposed sensor would significantly contribute to the overall study of the Earth carbon cycle by enabling three dimensional measurements of CO2. More specific research areas include carbon chemistry and surface CO2 flux studies, CO2 exchange between marine biosphere and ocean, ocean CO2 circulation, and evaluation of CO2 seeps at ocean ridges and submarine volcanoes to understand deep carbon pathways to the oceans. Good spatial and temporal sampling, including at depth, are also potentially applicable to studies of small-scale or dynamic CO2 distributions, for validating CO2 sequestration experiments and for monitoring oil drilling operations.While we will be demonsrating our technique on CO2, the sensor concepts are widely applicable to the sensing of any molecular species dissolved in liquids. As such other numerous applications would be unlocked such as applications to water quality studies, or industrial characterisation of liquid contamination.