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.
<p>Currently sampling of the atmosphere for gas emission measurements involves building towers or hiring airplanes - capital-intensive methods. Easy access to unmanned aerial vehicles (UAV) has opened-up new opportunities for remote gas sampling. The project Iso-2-Drone aims to develop and produce a modular UAV-based gas monitoring system for emission measurements to substitute current technologies. A key feature of the UAV-attached gas sampler design was the ready-to-use nature of the system. This meant that the system was designed to mesh with commonly available equipment, using collection vessels which can be easily and immediately measured by common continuous flow - isotope ratio mass spectrometer (CF-IRMS) instrumentation. The target compounds comprise the three major natural greenhouse gases CH<sub>4</sub>, CO<sub>2</sub> and N<sub>2</sub>O to be measured at natural isotopic abundance and ambient levels.</p><p>We use 20 mL headspace vials for CH<sub>4</sub> and CO<sub>2</sub> sampling. Vials can be conditioned on-sight with our sample preparation prototype using repeatedly evacuating and synthetic air refilling cycles to prevent ambient air contamination. On the UAV-attached sampler atmospheric air is sampled passively by pressure compensation of the vacuum. N<sub>2</sub>O is sampled actively via adsorption tubes, filled with Molecular Sieve 5&#197; and conditioned in the lab. Both a prototype device and two UAV-attached samplers have been designed, built and are currently tested.</p><p>The measurement setup in the lab comprises of two autosamplers, a purge & trap system (VSP 4000, IMT Innovative Maschinentechnik GmbH) and a headspace sampler (CTC CombiPal, Chromtech GmbH) in order to switch from ppb range necessary for CH<sub>4 </sub>and N<sub>2</sub>O to a ppm range for CO<sub>2</sub>. For CO<sub>2 </sub>measurements the CTC injects 600 &#181;l of sampled air to a Restek Micropacked Column (Shin Carbon ST 100/120, 2m x 1mm ID and 1/16&#8221; OD) within a Thermo Scientific Trace GC Ultra heated up from 40&#176;C to 110&#176;C, maintained for 5 min, before heating up to 180&#176;C by 12&#176;C per minute. Thereby CO<sub>2</sub> is properly separated from the potentially interfering N<sub>2</sub>O. For CH<sub>4</sub> the residual air sample is cryo-focused at -140&#176;C in a HayeSep D filled trap, transferred to the GC and targeted with a Poraplot Q (30m x 0.32mm) held at 35&#176;C. Using the similar GC method and autosampler N<sub>2</sub>O is desorbed after switching the autosampler to thermal desorption mode. All three analytes pass an oxidation/reduction reactor (1030&#176;C) before they are introduced into the IRMS (Thermo Scientific DeltaV Advantage) via a universal gas interface (Thermo Scientific Conflo IV). The IRMS continuously scans the intensity of the mass-to-charge ratios of mass 44, 45, 46 for CH<sub>4</sub> and CO<sub>2</sub> and 28, 29 for N<sub>2</sub>0 converted to N<sub>2</sub>. &#948;<sup>13</sup>C and &#948;<sup>15</sup>N are referenced against calibrated laboratory reference gases.</p><p>We are currently tuning the methods and testing the prototypes and will present the lasted results and open questions at the conference.</p>
Abstract. The study herein reports on the development of two sampling devices and the subsequent analytical setup for the sampling and analysis of atmospheric trace gases. Both samplers can be mounted to an unmanned aerial vehicle (UAV), the targeted compounds were greenhouse gases (e.g. CO2, CH4) and volatile organic compounds (VOC, i.e. chlorinated ethenes), for all compounds mole fraction and the stable carbon isotope ratio were measured. 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 collect and sampled in glass vials for greenhouse gas analysis. The measurement setup for the sorbent tubes achieved analyte mass recovery rates of 63 %–100 % (more favourable for lower chlorinated VOCs), when prepared from gaseous or liquid calibration standards, and reached a precision better than 0.7 ‰ for δ13C in the molar ratio range of 0.35–4.45 nmol. The precision of triplicate CO2 measurements from whole air sample replicates was < 7.3 mmol mol-1 and < 0.3 ‰ and < 0.03 µmol mol-1 and < 0.24 ‰ for CH4 working gas standard replicates. The UAV-equipped samplers were tested over two field sampling campaigns designed to (1) compare UAV-collected and manually 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 results emphasized the functionality of the sampling and measurement setup described, demonstrating that it a viable tool for monitoring atmospheric trace gas inventories and identifying emission sources.
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