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.

Abstract. The study herein reports on the development and testing of sampling systems (and subsequent analytical setups) that were deployed on an unmanned aerial vehicle (UAV) for the purpose of analysing greenhouse gases (GHGs) and volatile organic compounds (VOCs) in the lower atmospheric boundary layer. Two sampling devices, both of which can be mounted to an UAV with a payload capability greater than 1 kg, were tested for respective sampling and analysis of specific GHGs (carbon dioxide, CO2, and methane, CH4) and VOCs (chlorinated ethenes, CEs). The gas analyses included measurements of the molar amounts and the respective stable carbon isotope ratios. In addition to compound calibration in the laboratory, the functionality of the samplers and the UAV-based sampling was tested in the field. Atmospheric air was either flushed through sorbent tubes for VOC sampling or collected and sampled in glass vials for GHG analysis. The measurement setup for the sorbent tubes achieved analyte mass recovery rates of 63 %–100 % (more favourable for lower chlorinated ethenes), when prepared from gaseous or liquid calibration standards, and reached a precision (2σ) better than 0.7 ‰ for δ13C values in the range of 0.35–4.45 nmol. The UAV-equipped samplers were tested over two field sampling campaigns designed to (1) compare manual and UAV-collected samples taken up a vertical profile at a forest site and (2) identify potential emissions of CO2, CH4 or VOC from a former domestic waste dump. The precision of CO2 measurements from whole air samples was ≤7.3 µmol mol−1 and ≤0.3 ‰ for δ13C values and ≤0.03 µmol mol−1 and ≤0.2 ‰ for CH4 working gas standards. The results of the whole air sample analyses for CO2 and CH4 were sufficiently accurate to detect and localise potential landfill gas emissions from a secured former domestic waste dump using level flight. Vertical CO2 profiles from a forest location showed a causally comprehensive pattern in the molar ratios and stable carbon isotope ratios but also the potential falsification of the positional accuracy of a UAV-assisted air sample due to the influence of the rotor downwash. The results demonstrate that the UAV sampling systems presented here represent a viable tool for atmospheric background monitoring, as well as for evaluating and identifying emission sources. By expanding the part of the lower atmosphere that can be practicably sampled over horizontal and vertical axes, the presented UAV-capable sampling systems, which also allow for compound-specific stable isotope analysis (CSIA), may facilitate an improved understanding of surface–atmosphere fluxes of trace gas.

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<p>Cities contribute significantly to global carbon dioxide (CO<sub>2</sub>) emissions, and it is important to understand and accurately measure these emissions in order to effectively mitigate climate change. Current methods for estimating emissions, such as emission inventories, can be very uncertain at the scale of individual cities. Measurement methods that involve analyzing local atmospheric CO<sub>2</sub> levels and the respective stable carbon isotopic composition of CO<sub>2</sub> can provide additional, independent information on local emissions, particularly in terms of source contributions from combustion of different fossil fuels and natural respiration. As part of the Vienna Urban Carbon Laboratory (VUCL), a cavity-ring-down laser isotope spectrometer (G2201-<em>i</em>, Picarro Inc., USA) has been operating on a radio tower in Vienna’s city centre since May 2022 to measure atmospheric mixing ratios of CO<sub>2</sub> and stable carbon isotopic composition of CO<sub>2</sub> (δ<sup>13</sup>C) 144 m above the surface.</p> <p>The overall objective here is to establish an analysis framework to best utilize these measurements in combination with tall-tower eddy covariance measurements for the identification and quantification of local CO<sub>2</sub> emission emitters in Vienna. Initial analysis of the half-hourly CO<sub>2</sub> concentrations and fluxes between May and Dec 2022 show that a night-time increase of measured CO<sub>2</sub> concentrations are followed by an early morning peak, due to a nocturnal build-up of surface-level CO<sub>2</sub> that is followed by an upward flush of CO<sub>2</sub> in the morning. The δ<sup>13</sup>C of CO<sub>2</sub> (based on keeling plot analysis) suggests that fluxes from natural respiration are dominant over the night. In the afternoon, the δ<sup>13</sup>C of CO<sub>2</sub> sources decreases, which may be due to an increased contribution from sources with isotopically depleted CO<sub>2</sub>, such as traffic emissions and small-scale stationary methane combustion. We also observed higher concentrations CO<sub>2</sub> that are isotopically depleted, during the summer when winds came from the area southeast of the tower, which has more industrial and refinery activity. In addition to these initial results from keeling plot analysis, our presentation will also include results from the ongoing winter measurements, where we expect to see indications of enhanced methane combustion for space heating. Furthermore, results from ongoing tests of other analysis methods for identifying emitting sources (e.g., application of the miller trans model method, analysis of the data at higher temporal resolutions) will be presented.</p>

Reductive dechlorination performed by organohalide-respiring bacteria (OHRB) enables the complete detoxification of certain emerging groundwater pollutants such as perchloroethene (PCE). Environmental samples from a contaminated site incubated in a lab-scale microcosm (MC) study enable documentation of such reductive dechlorination processes. As compound-specific isotope analysis is used to monitor PCE degradation processes, nucleic acid analysis-like 16S-rDNA analysis-can be used to determine the key OHRB that are present. This study applied both methods to laboratory MCs prepared from environmental samples to investigate OHRB-specific isotope enrichment at PCE dechlorination. This method linkage can enhance the understanding of isotope enrichment patterns of distinct OHRB, which further contribute to more accurate evaluation, characterisation and prospection of natural attenuation processes. Results identified three known OHRB genera (Dehalogenimonas, Desulfuromonas, Geobacter) in diverse abundance within MCs. One species of Dehalogenimonas was potentially involved in complete reductive dechlorination of PCE to ethene. Furthermore, the isotopic effects of PCE degradation were clustered and two isotope enrichment factors (ε) (- 11.6‰, - 1.7‰) were obtained. Notably, ε values were independent of degradation rates and kinetics, but did reflect the genera of the dechlorinating OHRB.