the field against IRMS concentrations from collected samples. The different colors represent different years between 2008 and 2012. The shapes represent collections above, around, and away from the source. The black line is the 1:1 line (perfect agreement), while the red and blue dashed lines represent ± 10% and ± 20% relative agreement, respectively.
Figure 3.10 The remote FMS instrument was deployed to the ZERT controlled‐release field site. The instrument remained in the weatherproof case and the laser was directed to the corner cube identified by the orange arrow.
Unlike the in situ instrument that would analyze a point source of atmosphere, the remote FMS instrument measured a column average of CO2 in the atmosphere. As one might expect, the CO2 stable isotope ratio changes with both the flux of CO2 that seeped to the surface along the observed column as well as due to changes in weather. This instrument was deployed in 2010 and 2011 and monitored δ13C ~ ‐9% to ‐28% and δ13C ~ ‐6% to ‐28%, respectively. Recall that the atmosphere has a natural CO2 stable isotope ratio of ‐7% and these results were in good agreement with background levels when seepage did not reach the surface. The instrument also recorded concentrations up to ‐28%, about half of the maximum value observed by the in situ instrument and well below the ‐15% that would have clearly indicated seepage. While the remote instrument is capable of identifying the presence of a leak, it is not capable of determining the exact position or positions of the leak as a point source detector could.
3.6. CONCLUSION
Geologic sequestration of carbon dioxide is one method to permanently store CO2 industrial emissions and reduce the atmospheric concentration of this greenhouse gas. While some sequestered CO2 is expected to react with the surface of the reservoir and mineralize, much of the injected CO2 will remain as a fluid with the reservoir and monitoring, verification, and accounting for this CO2 is required. In this chapter, we described several available methods for monitoring CO2 emissions from a sequestration site from the surface. However, monitoring from the surface is complicated by natural CO2 emissions at the surface, and the diurnal cycle.
A wide variety of commercial and laboratory monitoring instruments have been developed and field tested. Passive and active absorption spectroscopy can measure the absolute concentration of atmospheric CO2, and seepage from the sequestration site is derived from changes from the background diurnal concentrations. Absorption spectroscopy also has the advantage of point source in situ analysis as well as wide area remote analysis of the area above the sequestration site.
MVA methods that are capable of measuring the carbon stable isotope ratio have the advantage of distinguishing the anthropogenic CO2 from the sequestration site and the natural CO2 emissions. CRS and FMS are sensitive methods of accurately measuring the 13CO2 and 12CO2 ratio. While CRS is limited to in situ analysis on a collected sample, FMS has been done as both in situ and remote, open source, configurations.
ACKNOWLEDGMENTS
The preparation of the manuscript was supported by the Laboratory Directed Research and Development Program at Los Alamos National Laboratory under project number 20180066DR. We gratefully acknowledge the Department of Energy, National Energy Technology Laboratory, for supporting the field work reported here.
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