Comparison of in situ field measurements of water vapour and stable carbon isotopologues of carbon dioxide from laser spectroscopic instruments

Description

Anthropogenic sources of carbon dioxide represent a significant portion of the global carbon budget, and attributing atmospheric CO2 abundances to their biogenic and anthropogenic sources will require accurate measurements of CO2 concentrations from multiple sensors. We conducted an intensive field campaign in fall 2010 to measure CO2 and several tracers for its sources using a new mobile laboratory. Two trucks carrying instruments for greenhouse gases were deployed along with a gas-calibration system. Air was drawn into both trucks from a 10-m tall mast. All measurements were made either from a common inlet or closely located inlets. We used four instruments to make high-frequency laser-spectroscopic measurements of abundances of CO2 and its stable isotopologue (13CO2). Each of these instruments simultaneously measured abundances of water vapor. Automated flask samplers collected whole air samples for offline analysis of CO2 abundances and δ13C-CO2. We obtained good agreement among CO2 measurements from these instruments following careful post-processing and calibrations. Good agreement was also demonstrated for water vapor measurements. Differences between δ13C-CO2 measured by two of these instruments, however, were larger than expected.