Successive and automated stable isotope analysis of CO2, CH4 and N2O paving the way for unmanned aerial vehicle-based sampling

Rationale Measurement of greenhouse gas (GHG) concentrations and isotopic compositions in the atmosphere is a valuable tool for predicting their sources and sinks, and ultimately how they affect Earth's climate. Easy access to unmanned aerial vehicles (UAVs) has opened up new opportunities for remote gas sampling and provides logistical and economic opportunities to improve GHG measurements. Methods This study presents synchronized gas chromatography/isotope ratio mass spectrometry (GC/IRMS) methods for the analysis of atmospheric gas samples (20-mL glass vessels) to determine the stable isotope ratios and concentrations of CO2, CH4 and N2O. To our knowledge there is no comprehensive GC/IRMS setup for successive measurement of CO2, CH4 and N2O analysis meshed with a UAV-based sampling system. The systems were built using off-the-shelf instruments augmented with minor modifications. Results The precision of working gas standards achieved for delta C-13 and delta O-18 values of CO2 was 0.2 parts per thousand and 0.3 parts per thousand, respectively. The mid-term precision for delta C-13 and delta N-15 values of CH4 and N2O working gas standards was 0.4 parts per thousand and 0.3 parts per thousand, respectively. Injection quantities of working gas standards indicated a relative standard deviation of 1%, 5% and 5% for CO2, CH4 and N2O, respectively. Measurements of atmospheric air samples demonstrated a standard deviation of 0.3 parts per thousand and 0.4 parts per thousand for the delta C-13 and delta O-18 values, respectively, of CO2, 0.5 parts per thousand for the delta C-13 value of CH4 and 0.3 parts per thousand for the delta N-15 value of N2O. Conclusions Results from internal calibration and field sample analysis, as well as comparisons with similar measurement techniques, suggest that the method is applicable for the stable isotope analysis of these three important GHGs. In contrast to previously reported findings, the presented method enables successive analysis of all three GHGs from a single ambient atmospheric gas sample.