基于TDLAS技术的海水中溶存CO_(2)原位测量实验研究  

The Experimental Research on In-Situ Detection for Dissolved CO_(2) in Seawater Based on Tunable Diode Laser Absorption Spectroscopy

作　　者：杜保鲁 李萌[1] 郭金家[1] 张志浩 叶旺全 郑荣儿[1] DU Bao-lu;LI Meng;GUO Jin-jia;ZHANG Zhi-hao;YE Wang-quan;ZHENG Rong-er(College of Information Science&Engineering,Ocean University of China,Qingdao 266100,China)

机构地区：[1]中国海洋大学信息科学与工程学院,山东青岛266100

出　　处：《光谱学与光谱分析》2022年第4期1264-1269,共6页Spectroscopy and Spectral Analysis

基　　金：国家自然科学基金重大科研仪器研制项目(41527901);山东省重大科技创新工程项目(20195ZZY010417);中央高校基本科研业务费(201962003)资助。

摘　　要：海洋与大气交换的CO_(2)通量是研究海-气之间碳循环过程及海洋酸化问题的重要指标,其估算方法主要依赖于海水中CO_(2)的测量。可调谐半导体激光吸收光谱(TDLAS)作为一种常用的气体浓度检测技术,因其具有较好的环境适应性、选择性和较高的灵敏度,亦可发挥出水中溶存气体原位测量的潜力。为验证将TDLAS技术应用到海洋中溶存CO_(2)原位探测的可行性,将渗透膜脱气技术与实验室研发的TDLAS气体探测样机相结合,实现了海水中溶存CO_(2)的原位探测。为适应水下的复杂环境,样机整体被设计为铝合金密封舱结构,具有良好的密封性、耐压性与耐腐蚀性。激光光源采用中心波数位于4 990 cm^(-1)的DFB激光器,其波数扫描范围为4 992~4 994.5 cm^(-1),可覆盖CO_(2)在4 992.51和4 993.74 cm^(-1)的相邻两条吸收谱线。渗透膜采用具有优秀耐压性与透气性的Teflon AF-2400 X,可满足样机在深水区长期探测的目的。为兼顾较高探测灵敏度与较快响应速率双重指标要求,样机采用了一种小型化多次反射式气体吸收池,有效吸收光程可达8 m,内部仅需气体量24 mL,具有良好的吸收特性。在实验室对样机进行校正实验,使用样机对5种不同浓度(202.8×10^(-6),503×10^(-6),802×10^(-6),1 006×10^(-6)和2 019×10^(-6))的标准CO_(2)气体进行测量,测量值与实际值的线性相关度R^(2)高达99.94%,最大相对误差小于8%,减小了样机误差对测量值的影响。为评估样机长时间工作的稳定性,使用样机对浓度为802×10^(-6)的标准CO_(2)气体进行了30 min的连续测量,平均测量浓度为802.6×10^(-6),其波动范围仅为10×10^(-6),样机精度约为0.5%,可满足水中溶存气体探测的要求。选取水深3米的近海码头进行试验,成功获得了24 h水中CO_(2)的典型吸收光谱及浓度时间序列测量结果,验证了样机水下工作的能力与稳定性。通过在东海海域五处不同深度的区域�The exchange flux of CO_(2) between the ocean and the atmosphere is an important indicator for studying the carbon cycle and the ocean acidification issue.The estimation of CO_(2) flux mainly depends on the detection of CO_(2) in seawater.As a widely used gas detection technology,Tunable Diode Laser Absorption Spectroscopy(TDLAS) has advantages in environmental adaptability,selectivity and good sensitivity,and thus it is potential in the in-situ detection for dissolved gas in seawater.In order to verify the feasibility of applying TDLAS technology to the in-situ detection for dissolved CO_(2) in the seawater,this paper integrates the permeable membrane which realizes gas-water separation with the TDLAS gas detection prototype developed in the laboratory to realize the in-situ detection for CO_(2) in seawater.The whole prototype is designed as a sealed cabin.The prototype’s material is aluminum alloy which has good tightness,pressure and corrosion resistance.The laser source uses a DFB laser with a central wavenumber of 4 990 cm^(-1),and its wavenumber is scanned from 4 992 to 4 994.5 cm^(-1) over time,which can contain two absorption lines of CO_(2) at 4 992.51 and 4 993.74 cm^(-1).The permeable membrane’s material uses Teflon AF-2400 X with excellent pressure resistance and air permeability.Considering of requirements of high detection sensitivity and fast response rate for the prototype in underwater,the prototype uses a miniaturized Herriott-type multi-reflection cavity with good absorption characteristics.The cavity can achieve an effective optical path of 8 meters and a gas sampling volume of only 24 mL.A calibration experiment was done in the laboratory to reduce the influence of the prototype error on the measured value.Five different concentration(202.8×10^(-6),503×10^(-6),802×10^(-6),1 006×10^(-6),2 019×10^(-6)) standard CO_(2) gases were measured by the prototype.The linear correlation(R^(2)) is 99.95% between measured values,and actual values and the prototype has a maximum relatively error �

关 键 词：溶存CO_(2)气体 可调谐半导体激光吸收光谱 渗透膜 原位测量 

分 类 号：TN219[电子电信—物理电子学]