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

Abstract

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 δ13C and δ18O values of CO2 was 0.2‰ and 0.3‰, respectively. The mid‐term precision for δ13C and δ15N values of CH4 and N2O working gas standards was 0.4‰ and 0.3‰, 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‰ and 0.4‰ for the δ13C and δ18O values, respectively, of CO2, 0.5‰ for the δ13C value of CH4 and 0.3‰ for the δ15N 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.

A UAV-based sampling system to analyse greenhouse gases and volatile organic carbons encompassing compound specific stable isotope analysis

“…Here we present a sampling system coupled to an off-line measurement setup to measure the atmosphere for CO2, CH4, and VOC molar ratios and δ 13 C-value at ambient conditions. Two samplers and a whole-air sample vessel preparation device were developed and evaluated at field conditions, while the measurement setup was evaluated in prior experiments (Leitner et al, 2020). That measurement setup enabled the determination of the mole fraction and stable isotope ratio of carbon of the target compounds detailed herein and can be further applied to investigate the isotope ratios of hydrogen, oxygen and nitrogen in nitrous oxide.…”

“…CE and reference materials were both sampled in tin cups designed for sampling liquids. The CO2 and CH4 working gas was calibrated against two isotope certified CO2 gas standards (-6.7‰ ± 0.2‰, -39.0‰ ± 0.2‰, ISO-TOP, Messer Austria GmbH) after direct injection to a GC-C-IRMS measurement setup, as presented elsewhere (Leitner et al, 2020). Obtained δ 13 C values ± 1 σ were -4.34‰ ± 0.2‰ (n=17) and -40.3‰ ± 0.2‰ (n=38)…”

“…The measurement procedure and the calibration standard preparation for the analysis of CO2 and CH4 (molar ratio and 13 C/ 12 C ratio) is reported in details in a preceding publication of Leitner et al (2020). The analysis of CO2 (detection limit of 100 µmol mol -1 ) was carried out with head-space (HS) GC-C-IRMS analysis.…”

“…Independent single samples were taken, which were analysed for the carbon isotope ratio and mole fraction of CO2 and CH4. Each compound was measured sequentially using a different measurement setup (Leitner et al, 2020), having been sampled using the same sample vessel and filled at the waste dump. First, CO2 was analysed from triplicate injections of 300 µL each, before analysing the residual volume (~19.6 mL) for CH4.…”

“…The precision in molar ratio was ±2 µmol mol -1 for CO2 and 0.11 µmol mol -1 for CH4. Detailed information is provided in Leitner et al (2020).…”