The Development and Application of a New High Precision GC-IRMS Technique for N2O-Free Isotopic Analysis of Atmospheric CO2

• Main Author: Ferretti, Dominic Francesco
• Other Authors: McGregor, Jim, Lowe, Dave
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Victoria University of Wellington 1999
• Subjects: Atmospheric chemistry; Carbon cycle (Biogeochemistry); Atmospheric carbon dioxide; Arctic; Grim; New Zealand; Scripps; Institute of Arctic and Alpine Research
• Online Access: http://researcharchive.vuw.ac.nz/handle/10063/737

A new GC-IRMS technique has been developed for isotopic and mixing ratio analysis of atmospheric CO2. The technique offers for the first time, N2O-free, high precision (<0.05 [per mil]) analysis of d13C and d18O from small whole-air samples. On-line GC separation of CO2 and N2O from these small samples is combined with IRMS under elevated ion source pressures. A specialised open split interface is an integral part of the inlet system and ensures a continuous flow of either sample gas or pure helium to the IRMS. The analysis, including all flushing, uses a total of 45 ml of an air sample collected at ambient pressure. Of this, three 0.5 ml aliquots are injected onto the GC column, each providing [approximately] 0.8 nmol CO2 in the IRMS source. At this sample size, d13C precision obtained is at the theoretical shot-noise limit. Demonstrated precisions for d13C, d18O, and CO2 mixing ratio (all measured simultaneously)are 0.02 [per mil], 0.04 [per mil] and 0.4 ppm respectively. The initial results from an inter calibration exercise with Atmospheric Research at the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia achieved the International Atomic Energy Agency (IAEA) target precision for d13C. During this exercise, agreement for d18O and CO2 mixing ratio was outside the IAEA and World Meteorological Organization (WMO) target precisions for these species, however, when the measurement uncertainties of the two laboratories were considered, the differences were not significant. An inter comparison program using air samples collected at Baring Head, New Zealand and Cape Grim, Australia was also established with CSIRO and d13C, d18O and CO2 mixing ratio showed excellent agreement when combined measurement uncertainties were considered. Further inter comparisons with the Carbon Cycle Group at the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory (NOAA CMDL), the Institute of Arctic and Alpine Research (INSTAAR), and Scripps Institution of ...