Development of an ultra-fast method for continuous and automated analysis of dissolved greenhouse gases in surface waters

自然沃茨，如海洋、湖泊和河流，是全球最大的温室气体储存库，与大气进行积极的交换。 这些气体在溶解的水相和大气之间的扩散通量包括区域和全球的显著通量。 以前用于确定地表水浓度和空气-水通量的技术主要集中在收集小瓶中的离散地表水样品或使用双头平衡器。 虽然收集离散样本可以提供准确的结果，但对自然环境的相对粗糙的采样可能导致地表水温室气体浓度特征的真实程度的不确定性。 喷淋头平衡器为更高分辨率的绘图提供了近乎连续的数据，但低溶解度气体（如甲烷）的缓慢响应时间可能会使其结果在快速变化的溶解气体浓度期间不准确。 有趣的是，在过去的几年里，一些研究产生的数据表明，某些溶解的温室气体的通量在极端局部地区被积极地排放到大气中。 然而，目前还没有技术来定量地发现和绘制这些特征的全部范围，本项目将充分开发一种新技术，用于连续分析表层沃茨中溶解的温室气体浓度和自然同位素。 这一新系统的主要优势是对地表水溶解温室气体浓度变化的超快响应时间，同时仍保持高精度和精确度分析。 更具体地说，这项技术将测量溶解的甲烷，二氧化碳，一氧化碳和一氧化二氮的浓度和天然稳定同位素。 工作原理是真空抽气。 水以每分钟15升的速率连续泵送通过透气膜，并在膜的外部施加真空以从水流中提取溶解的气体。 然后将提取的气体泵入分析检测器进行分析。 通过将水和提取气体的流速与在提取气体中测量的特定温室气体的浓度进行比较，可以确定溶解气体浓度。 该系统的主要缺点是瓦斯抽采效率不是100%。 因此，已经开发了一种集成的自动校准系统，以在预定的间隔量化溶解气体提取效率。 该系统的原型已经开发，并已在实验室和墨西哥湾北方进行了初步测试，显示结果是准确的，精确的，并能够检测浓度变化的亚分钟的时间尺度。 该项目将开发该技术直至完成，目标是针对一系列不同的温室气体、水的物理和化学性质以及萃取膜类型全面验证该系统。 将进行实验室测试和现场试验，目的是设计和验证一个用户友好、便携和完全自动化的系统，供科学界使用。 一名来自科学界代表性不足的研究生和六名本科生将参与这个项目。 所有这些学生科学家将有机会为整个科学过程做出贡献，从数据收集和解释到演示和出版。

Natural waters such as oceans, lakes, and rivers comprise the largest global reservoirs of numerous greenhouse gases in active exchange with the atmosphere. The diffusive fluxes of these gases between the dissolved aqueous phase and the atmosphere comprise significant fluxes regionally and globally. Previous techniques used to determine surface water concentrations and air-water fluxes primarily focus on collecting discrete samples of surface water in vials or the use of shower-head equilibrators. While collecting discrete samples provides accurate results, the relatively coarse sampling of the natural environment can lead to uncertainties in the true extent of surface water greenhouse gas concentration features. Shower-head equilibrators provide near-continuous data for higher resolution mapping, but the slow response time for gases of low solubility such as methane can render their results inaccurate during rapidly changing dissolved gas concentrations. Interestingly, the over the last few years, several studies have produced data suggesting that the flux of certain dissolved greenhouse gases are emitted to the atmosphere aggressively in extremely localized areas. However, the technology has not been available to quantitatively discover and map the full extent of these features.This project will fully develop a new technique for the continuous analysis of dissolved greenhouse gas concentrations and natural isotopes in surface waters. The main advantage of this new system is an ultra-fast response time to changes in the surface water concentration of dissolved greenhouse gases while still maintaining high accuracy and precision analyses. More specifically, this technique will measure dissolved methane, carbon dioxide, carbon monoxide, and nitrous oxide concentrations and natural stable isotopes. The principle of operation is vacuum gas extraction. Water is continually pumped through a gas-permeable membrane at a rate of 15 liters per minute and a vacuum is applied to the outside of the membrane to extract the dissolved gases from the water stream. The extracted gases are then pumped into an analytical detector for analysis. By comparing the water and extracted gas flow rates with the concentration of a specific greenhouse gas measured in the extracted gases, the dissolved gas concentration can be determined. The main weakness of this system is that the gas extraction efficiency is not 100%. Thus, an integrated and automated calibration system has been developed to quantify the dissolved gas extraction efficiency at predetermined intervals. A prototype of this system has been developed and preliminary tests have been conducted in the laboratory and northern Gulf of Mexico displaying results that are accurate, precise, and able to detect concentration changes on sub-minute timescales. This project will develop this technology to completion with the goal of fully validating the system for a suite of different greenhouse gases, physical and chemical water properties, and extraction membrane types. Laboratory tests and field trials will be conducted with the goal of engineering and validating a system that is user-friendly, portable, and fully automated for use within the scientific community. A graduate student from a group underrepresented in science will be involved in this project as will six undergraduate students. All of these student scientists will be given opportunities to contribute to the entire scientific process from data collection and interpretation to presentation and publication.