大气δ~13C红外光谱分析系统及标定方法评估

Evaluation of infrared spectroscopy systems and calibration strategies for atmospheric δ^(13)C measurement

利用外标法对大气CO_2及其δ~13C进行标定,并对3种不同的δ~13C(CO_2)标定方法进行比对评估,结果表明:FTIR和G2201i(WS-CRDS)在观测大气CO_2时均表现出较好的精度及线性相关性,而在观测δ~13C时,Allan方差结果显示相较于G2201i,FTIR具有更好的稳定性;经标气标定后CO_2观测结果准确度大大提高,待测目标气CO_2浓度误差不超过±0.05×10^(-6),FTIR和G2201i标定结果之间无显著差异(不超过±0.05×10-6);由两套系统直接测得的δ~13C值存在较大误差,经标定后其结果误差显著减小,FTIR由3种标定方法计算的结果误差均在±0.1‰以内,3种标定方法无显著差异;G2201i由第2种和第3种标定方法计算的结果误差也在±0.1‰以内,而第1种标定方法计算的结果误差则在±(0.1~0.2)‰之间。

Atmospheric δ～13C（ CO_2） high precision measurement was always based on mass spectroscopy technology,while the emerging isotope ratio infrared spectroscopy technology was rarely reported in domestic literatures. Compared to mass spectroscopy technology,the wavelength scanned cavity ringdown spectroscopy（ WS-CRDS） and Fourier transform infrared spectroscopy（ FTIR） can measure CO_2 and its δ13C continuously in ambient conditions,and the operation was more simple and convenient,but always susceptible to environmental conditions. Thus, to insure international comparability and compatibility of data,the performance of the two systems and the three calibration strategies for δ13C measurement were compared in the study,respectively. As a result,both FTIR and WS-CRDS showed good performance for atmospheric CO_2 concentration measurement, while for δ13C（ CO_2）,FTIR displayed higher stability than G2201 i. Calibration by standard gases can ensure accurate CO_2 measurement by the two systems,the errors for tested cylinders were all within ± 0. 05 × 10～（-6）,and the difference between CO_2 results measured by the two systems was also within ± 0. 05 × 10（-6）. After calibration by standard gases,the errors of δ～13C values can be reduced obviously. The errors of δ～13C values calibrated on FTIR were all within ± 0. 1‰ using three different calibration strategies,and no obvious difference was found among the three calibration strategies. The errors of δ13C values calibratedon G2201 i were within ± 0. 1‰ using the last two calibration strategies,while the errors of δ13C values calibrated on G2201 i using the first calibration strategy were within ± 0. 1 ～ 0. 2‰.