基于微型多次反射腔的TDLAS二氧化碳测量系统
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摘要
海气界面CO_2测量对于海洋科学研究具有重要意义,在目前的海洋CO_2测量仪器中,基于可调谐二极管激光吸收光谱技术(TDLAS)的设备因灵敏度高、环境适应性强等特点受到关注。TDLAS系统的体积和灵敏度通常受限于多次反射腔的大小和光程。针对海洋CO_2脱气量小且灵敏度高的测量需求,自主设计了一套微型多次反射腔,用于TDLAS系统的CO_2测量。该微型多次反射腔采用两片口径为25.4mm、焦距为50mm的球面反射镜,以38mm的腔长实现了253次反射,获得了约10m的光程,封装后的样品池体积仅有90mL。基于该微型多次反射腔搭建了一套直接吸收TDLAS的CO_2气体浓度测量系统,通过标准气体对该系统进行了测试,检测限约为26×10~(-6),不同浓度气体线性相关度R~2为99.986%。同时还将该系统与LGR公司生产的便携式温室气体分析仪(UGGA)进行了对比测量,结果表明二者在白天CO_2浓度波动较大和夜晚CO_2浓度变化较平稳两种情况下均表现出较好的一致性,R~2大于97%。实验结果证明了系统性能,下一步将优化试验装置并进行现场应用。
The measurement of CO_2at air-sea interface is significant to marine scientific research.There are many commercial instruments can be used for CO_(2 )measurements in marine environment,among which the instruments based on tunable diode laser absorption spectroscopy(TDLAS)play an important role due to the advantages of high sensitivity,good environmental adaptability,etc.As a core component of a TDLAS system,the volume and optical path of a multi-pass cavity limit the size and sensitivity of the system.For the application of underwater dissolved CO_(2 )measurements,due to the samll quantity of degassing gas and high sensitivity,both the small size and long optical path are required for a multi-pass cavity.In this work,a miniature multi-pass cavity was designed for the potential underwater dissolved CO_(2 )measurements.The miniature multi-pass cavity composed of two identical spherical mirrors(D=25.4 mm,f=50 mm)separated at a distance of 38 mm,realized 253reflection times,providing an effective optical path length of 10mand an inner volume of 90mL.Based on the miniature multi-pass cavity,a direct absorption TDLAS system was developed for CO_(2 )measurement.The system was evaluated with a series of different concentrations of CO_2standard gases.The obtained limit of detection(LOD)was about 26×10~(-6)(volume ratio),and the response was good linear with R~2=99.986%over the whole range.A commercial ultraportable greenhouse gas analyzer(UGGA)from Los Gatos Research(LGR)was also used for comparison measurements,and the results showed a consistent trend with R~2of more than 97%under conditions of both high fluctuation at daytime and low changes at nighttime in laboratory.The experiments testified the performance of the developed TDLAS system for CO_(2 )measurements,which means that the improved system will be used in field experiments in the near future.
The measurement of CO_2at air-sea interface is significant to marine scientific research.There are many commercial instruments can be used for CO_(2 )measurements in marine environment,among which the instruments based on tunable diode laser absorption spectroscopy(TDLAS)play an important role due to the advantages of high sensitivity,good environmental adaptability,etc.As a core component of a TDLAS system,the volume and optical path of a multi-pass cavity limit the size and sensitivity of the system.For the application of underwater dissolved CO_(2 )measurements,due to the samll quantity of degassing gas and high sensitivity,both the small size and long optical path are required for a multi-pass cavity.In this work,a miniature multi-pass cavity was designed for the potential underwater dissolved CO_(2 )measurements.The miniature multi-pass cavity composed of two identical spherical mirrors(D=25.4 mm,f=50 mm)separated at a distance of 38 mm,realized 253reflection times,providing an effective optical path length of 10mand an inner volume of 90mL.Based on the miniature multi-pass cavity,a direct absorption TDLAS system was developed for CO_(2 )measurement.The system was evaluated with a series of different concentrations of CO_2standard gases.The obtained limit of detection(LOD)was about 26×10~(-6)(volume ratio),and the response was good linear with R~2=99.986%over the whole range.A commercial ultraportable greenhouse gas analyzer(UGGA)from Los Gatos Research(LGR)was also used for comparison measurements,and the results showed a consistent trend with R~2of more than 97%under conditions of both high fluctuation at daytime and low changes at nighttime in laboratory.The experiments testified the performance of the developed TDLAS system for CO_(2 )measurements,which means that the improved system will be used in field experiments in the near future.
引文
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[3]ZHENG Wen-jing,HAN Yu,QIN Chuan,et al(郑文静,韩玉,秦川,等).Marine Environmental Science(海洋环境科学),2016,35(4):611.
[4]Zhang X,Kirkwood W J,Walz P M,et al.Applied Spectroscopy,2012,66(3):237.
[5]Fietzek P,Fiedler B,Steinhoff T,et al.Journal of Atmospheric&Oceanic Technology,2013,31(1):181.
[6]Pogány A,Wagner S,Werhahn O,et al.Applied Spectroscopy,2015,69(2):257.
[7]Chen H,Winderlich J,Gerbig C,et al.Atmospheric Measurement Techniques Discussions,2010,3(2):375.
[8]Mahesh P,Sreenivas G,Rao P V N,et al.International Journal of Remote Sensing,2015,36(22):5754.
[9]SHEN Chao,ZHANG Yu-jun,NI Jia-zheng(沈超,张玉钧,倪家正).Infrared(红外),2012,33(12):1.
[10]XIA Hua,DONG Feng-zhong,TU Guo-jie,et al(夏滑,董凤忠,涂郭结,等).Acta Optica Sinica(光学学报),2010,30(9):2596.
[11]Xia H,Tu G J,Pang T,et al.Journal of Measurement Science&Instrumentation,2011,2(4):402.
[12]Krzempek K,Jahjah M,Lewicki R,et al.Applied Physics B,2013,112(4):461.
[13]Ren W,Jiang W,Tittel F K.Applied Physics B,2014,117(1):245.
[14]Liu K,Wang L,Tan T,et al.Sensors&Actuators B Chemical,2015,220:1000.
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