A UAV-based active AirCore system for measurements of greenhouse gases

Abstract

Abstract.We developed and field-tested an unmanned aerial vehicle (UAV)-based active AirCore for atmospheric mole fraction measurements of CO 2 , CH 4 , and CO. The system applies an alternative way of using the AirCore technique invented by NOAA. As opposed to the conventional concept of passively sampling air using the atmospheric pressure gradient during descent, the active AirCore collects atmospheric air samples using a pump to pull the air through the tube during flight, which opens up the possibility to spatially sample atmospheric air. The active AirCore system used for this study weighs ∼ 1.1 kg. It consists of a ∼ 50 m long stainlesssteel tube, a small stainless-steel tube filled with magnesium perchlorate, a KNF micropump, and a 45 µm orifice working together to form a critical flow of dried atmospheric air through the active AirCore. A cavity ring-down spectrometer (CRDS) was used to analyze the air samples on site not more than 7 min after landing for mole fraction measurements of CO 2 , CH 4 , and CO. We flew the active AirCore system on a UAV near the atmospheric measurement station at Lutjewad, located in the northwest of the city of Groningen in the Netherlands. Five consecutive flights took place over a 5 h period on the same morning, from sunrise until noon. We validated the measurements of CO 2 and CH 4 from the active AirCore against those from the Lutjewad station at 60 m. The results show a good agreement between the measurements from the active AirCore and the atmospheric station (N = 146; R 2 CO 2 : 0.97 and R 2 CH 4 : 0.94; and mean differences: CO 2 : 0.18 ppm and CH 4 : 5.13 ppb). The vertical and horizontal resolution (for CH 4 ) at typical UAV speeds of 1.5 and 2.5 m s −1 were determined to be ±24.7 to 29.3 and ±41.2 to 48.9 m, respectively, depending on the storage time. The collapse of the nocturnal boundary layer and the buildup of the mixed layer were clearly observed with three consecutive vertical profile measurements in the early morning hours. Besides this, we furthermore detected a CH 4 hotspot in the coastal wetlands from a horizontal flight north to the dike, which demonstrates the potential of this new active AirCore method to measure at locations where other techniques have no practical access.

Studying boundary layer methane isotopy and vertical mixing processes at a rewetted peatland site by unmanned aircraft system

“…14). During the first flights in the early morning, under stable stratifications, an 25 enhanced methane concentration in the ABL can be expected, as observed by Andersen et al (2018) above wetlands. This is the case on both measurement days with the UAS.…”

“…First applications of measuring the methane concentration with UAS have been demonstrated: The air sampling inlet integrated into multirotor systems is either directly connected to the ground-based methane analyser via a sampling line (Brosy et al, 2017), or the air is stored in a tubing, which is analysed after the flight with a cavity ring down spectrometer (Andersen et al, 2018). The limiting element for both techniques is the length and weight of the sampling line or tube, and sampling altitudes up to 50 m have been published 5 (Brosy et al, 2017;Wolf et al, 2017;Andersen et al, 2018). An air sampling concept based on filling evacuated stainless steel containers by remotely opening a valve and subsequent chemical analyses of trace gases and first applications on multicopter systems have been shown (Chang et al, 2016(Chang et al, , 2018.…”

Wind Profiling in the Lower Atmosphere from Wind-Induced Perturbations to Multirotor UAS

“…How the ABL evolves with space and time influences phenomena that impact public health and safety [1][2][3][4][5]. For example, the transport of air pollutants, pollen and spores [6][7][8][9], wind power supply to smart grid systems [10][11][12][13][14], forecast of local weather [2][3][4][5], air traffic control at airports [15][16][17][18], the spread and management of wildfires [19][20][21][22], and emissions mitigation of greenhouse gases [23][24][25][26] are all affected by the dynamic state of the ABL. Therefore, mitigation of adverse conditions affected by the dynamic state of the ABL requires accurate measurements of wind velocity over micro-and mesoscale domains [2,27,28].…”

A Near-Field Gaussian Plume Inversion Flux Quantification Method, Applied to Unmanned Aerial Vehicle Sampling

“…Brosy et al [51] connected a small UAV to a high-precision in-situ sensor on the ground using 70 m of tubing to investigate methane altitude gradients. Andersen et al [69] used their AirCore system to collect a time-continuous air sample on a small UAV platform, which they later analysed on the ground, resulting in a 0.5 Hz precision of 0.5 ppb, to investigate methane altitude profiles. Emran et al [70] attached a cheap sensor to a small UAV platform to make remote sensing measurements between the ground and the UAV at a fixed height in order to map a landfill emission plume.…”