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The Total Carbon Column Observing Network (TCCON) and the Infrared Working Group of the Network for the Detection of Atmospheric Composition Change (NDACC-IRWG) are two ground-based networks that provide the retrieved concentrations of up to 30 atmospheric trace gases, using solar absorption spectrometry. Both networks provide reference measurements for the validation of satellites and models. TCCON concentrates on long-lived greenhouse gases (GHGs) for carbon cycle studies and validation. The number of sites is limited, and the geographical coverage is uneven, covering mainly Europe and the USA. A better distribution of stations is desired to improve the representativeness of the data for various atmospheric conditions and surface conditions and to cover a large latitudinal distribution. The two successive Fiducial Reference Measurements for Greenhouse Gases European Space Agency projects (FRM4GHG and FRM4GHG2) aim at the assessment of several low-cost portable instruments for precise measurements of GHGs to complement the existing ground-based sites. Several types of low spectral resolution Fourier transform infrared (FTIR) spectrometers manufactured by Bruker, namely an EM27/SUN, a Vertex70, a fiber-coupled IRCube, and a Laser Heterodyne spectro-Radiometer (LHR) developed by UK Rutherford Appleton Laboratory are the participating instruments to achieve the Fiducial Reference Measurements (FRMs) status. Intensive side-by-side measurements were performed using all four instruments next to the Bruker IFS 125HR high spectral resolution FTIR, performing measurements in the NIR (TCCON configuration) and MIR (NDACC configuration) spectral range. The remote sensing measurements were complemented by AirCore launches, which provided in situ vertical profiles of target gases traceable to the World Meteorological Organization (WMO) reference scale. The results of the intercomparisons are shown and discussed. Except for the EM27/SUN, all other instruments, including the reference TCCON spectrometer, needed modifications during the campaign period. The EM27/SUN and the Vertex70 provided stable and precise measurements of the target gases during the campaign with quantified small biases. As part of the FRM4GHG project, one EM27/SUN is now used as a travel standard for the verification of column-integrated GHG measurements. The extension of the Vertex70 to the MIR provides the opportunity to retrieve additional concentrations of N2O, CH4, HCHO, and OCS. These MIR data products are comparable to the retrieval results from the high-resolution IFS 125HR spectrometer as operated by the NDACC. Our studies show the potential for such types of spectrometers to be used as a travel standard for the MIR species. An enclosure system with a compact solar tracker and meteorological station has been developed to house the low spectral resolution portable FTIR systems for performing solar absorption measurements. This helps the spectrometers to be mobile and enables autonomous operation, which will help to complement the TCCON and NDACC networks by extending the observational capabilities at new sites for the observation of GHGs and additional air quality gases. The development of the retrieval software allows comparable processing of the Vertex70 type of spectra as the EM27/SUN ones, therefore bringing them under the umbrella of the COllaborative Carbon Column Observing Network (COCCON). A self-assessment following the CEOS-FRM Maturity Matrix shows that the COCCON is able to provide GHG data products of FRM quality and can be used for either short-term campaigns or long-term measurements to complement the high-resolution FTIR networks. [ABSTRACT FROM AUTHOR]

The Arctic and boreal regions are experiencing a rapid increase in temperature, resulting in a changing cryosphere, increasing human activity, and potentially increasing high-latitude methane emissions. Satellite observations from Sentinel-5P TROPOMI provide an unprecedented coverage of a column-averaged dry-air mole fraction of methane (XCH4) in the Arctic, compared to previous missions or in situ measurements. The purpose of this study is to support and enhance the data used for high-latitude research through presenting a systematic evaluation of TROPOMI methane products derived from two different processing algorithms: the operational product (OPER) and the scientific product (WFMD), including the comparison of recent version changes of the products (OPER, OPER rpro, WFMD v1.2, and WFMD v1.8). One finding is that OPER rpro yields lower XCH4 than WFMD v1.8, the difference increasing towards the highest latitudes. TROPOMI product differences were evaluated with respect to ground-based high-latitude references, including four Fourier Transform Spectrometer in the Total Carbon Column Observing Network (TCCON) and five EM27/SUN instruments in the Collaborative Carbon Column Observing Network (COCCON). The mean TROPOMI–TCCON GGG2020 daily median XCH4 difference was site-dependent and varied for OPER rpro from −0.47 ppb to 22.4 ppb, and for WFMD v1.8 from 1.2 ppb to 19.4 ppb with standard deviations between 13.0 and 20.4 ppb and 12.5–15.0 ppb, respectively. The TROPOMI–COCCON daily median XCH4 difference varied from −26.5 ppb to 5.6 ppb for OPER rpro, with a standard deviation of 14.0–28.7 ppb, and from −5.0 ppb to 17.2 ppb for WFMD v1.8, with a standard deviation of 11.5–13.0 ppb. Although the accuracy and precision of both TROPOMI products are, on average, good compared to the TCCON and COCCON, a persistent seasonal bias in TROPOMI XCH4 (high values in spring; low values in autumn) is found for OPER rpro and is reflected in the higher standard deviation values. A systematic decrease of about 7 ppb was found between TCCON GGG2014 and GGG2020 product update highlighting the importance of also ensuring the reliability of ground-based retrievals. Comparisons to atmospheric profile measurements with AirCore carried out in Sodankylä, Northern Finland, resulted in XCH4 differences comparable to or smaller than those from ground-based remote sensing. [ABSTRACT FROM AUTHOR]

The Total Carbon Column Observing Network (TCCON) and the Infrared Working Group of the Network for the Detection of Atmospheric Composition Change (NDACC-IRWG) are two ground-based networks that provide the retrieved concentrations of up to 30 atmospheric trace gases, using solar absorption spectrometry. Both networks provide reference measurements for the validation of satellites and models. TCCON concentrates on long-lived greenhouse gases (GHGs) for carbon cycle studies and validation. The number of sites is limited, and the geographical coverage is uneven, covering mainly Europe and the USA. A better distribution of stations is desired to improve the representativeness of the data for various atmospheric conditions and surface conditions and to cover a large latitudinal distribution. The two successive Fiducial Reference Measurements for Greenhouse Gases European Space Agency projects (FRM4GHG and FRM4GHG2) aim at the assessment of several low-cost portable instruments for precise measurements of GHGs to complement the existing ground-based sites. Several types of low spectral resolution Fourier transform infrared (FTIR) spectrometers manufactured by Bruker, namely an EM27/SUN, a Vertex70, a fiber-coupled IRCube, and a Laser Heterodyne spectro-Radiometer (LHR) developed by UK Rutherford Appleton Laboratory are the participating instruments to achieve the Fiducial Reference Measurements (FRMs) status. Intensive side-by-side measurements were performed using all four instruments next to the Bruker IFS 125HR high spectral resolution FTIR, performing measurements in the NIR (TCCON configuration) and MIR (NDACC configuration) spectral range. The remote sensing measurements were complemented by AirCore launches, which provided in situ vertical profiles of target gases traceable to the World Meteorological Organization (WMO) reference scale. The results of the intercomparisons are shown and discussed. Except for the EM27/SUN, all other instruments, including the reference TCCON spectrometer, needed modifications during the campaign period. The EM27/SUN and the Vertex70 provided stable and precise measurements of the target gases during the campaign with quantified small biases. As part of the FRM4GHG project, one EM27/SUN is now used as a travel standard for the verification of column-integrated GHG measurements. The extension of the Vertex70 to the MIR provides the opportunity to retrieve additional concentrations of N2O, CH4, HCHO, and OCS. These MIR data products are comparable to the retrieval results from the high-resolution IFS 125HR spectrometer as operated by the NDACC. Our studies show the potential for such types of spectrometers to be used as a travel standard for the MIR species. An enclosure system with a compact solar tracker and meteorological station has been developed to house the low spectral resolution portable FTIR systems for performing solar absorption measurements. This helps the spectrometers to be mobile and enables autonomous operation, which will help to complement the TCCON and NDACC networks by extending the observational capabilities at new sites for the observation of GHGs and additional air quality gases. The development of the retrieval software allows comparable processing of the Vertex70 type of spectra as the EM27/SUN ones, therefore bringing them under the umbrella of the COllaborative Carbon Column Observing Network (COCCON). A self-assessment following the CEOS-FRM Maturity Matrix shows that the COCCON is able to provide GHG data products of FRM quality and can be used for either short-term campaigns or long-term measurements to complement the high-resolution FTIR networks.

Monitoring of volatile organic compounds (VOCs) in air is crucial for understanding their atmospheric impacts and advancing their emission reduction plans. This study presents an innovative integrated methodology suitable for achieving semireal-time high spatiotemporal resolution three-dimensional measurements of VOCs from ground to hundreds of meters above ground. The methodology integrates an active AirCore sampler, custom-designed for deployment from unmanned aerial vehicles (UAV), a proton-transfer-reaction mass spectrometry (PTR-MS) for sample analysis, and a data deconvolution algorithm for improved time resolution for measurements of multiple VOCs in air. The application of the deconvolution technique significantly improves the signal strength of data from PTR-MS analysis of AirCore samples and enhances their temporal resolution by 4 to 8 times to 4-11 s. A case study demonstrates that the methodology can achieve sample collection and analysis of VOCs within 45 min, resulting in >120-360 spatially resolved data points for each VOC measured and achieving a horizontal resolution of 20-55 m at a UAV flight speed of 5 m/s and a vertical resolution of 5 m. This methodology presents new possibilities for acquiring 3-dimensional spatial distributions of VOC concentrations, effectively tackling the longstanding challenge of characterizing three-dimensional VOC distributions in the lowest portion of the atmospheric boundary layer.

Accurate measurements of the vertical distribution of carbon dioxide (CO2) in the atmosphere are critical to validate the vertical columns recorded by satellite and ground-based spectrometers and to estimate sources and sinks of CO2. This work describes an in-situ air-sampler system (Aircore). Profiles of CO2 and carbon monoxide (CO) were retrieved from two soundings of this system in Xilin Hot on 13 and 14 June 2018, and compared with observations from the Tropospheric Monitoring Instrument (TROPOMI), Orbiting Carbon Observatory-2 (OCO-2), and Copernicus Atmosphere Monitoring Service (CAMS). The column-averaged mixing ratio of CO (XCO) monitored by TROPOMI agreed well with that calculated from the in-situ CO profile, with a small mean difference of 5 ± 1.89 ppb. The column-averaged mixing ratio of CO2 (XCO2) monitored by OCO-2 also agreed well with that calculated from the in-situ CO2 profile, with a slight bias of 0.4 ± 0.6 ppm. The OCO-2 a posteriori profile had an obvious bias compared with the in-situ CO2 profile on 13 June, with an underestimation between 600 hPa and 250 hPa and an overestimation below 600 hPa. CAMS also had the same bias compared with the in-situ CO profile; however, CAMS agreed well with the in-situ CO profile on 14 June in the troposphere because a weak cold vortex passed Xilin Hot on 13 June and disappeared on 14 June. In the stratosphere, there were significant biases in the vertical degradation. The striking agreement between the column-averaged mixing ratios and the differences in the vertical distribution suggests new exciting applications for the profile product.

Airborne measurements offer an effective way to quantify urban emissions of greenhouse gases (GHGs). However, it may be challenging due to the requirement of high measurement precision and sufficiently enhanced signals. We developed a new active AirCore system based on the previous unmanned aerial vehicle (UAV) version, which is capable of sampling atmospheric air for several hours aboard a lightweight aircraft for postflight simultaneous and continuous measurements of N 2 O, CH 4 , CO 2 , and CO. We performed 13 flights over the urban areas of Groningen, Utrecht, and Rotterdam and evaluated the aircraft-based AirCore measurements against in situ continuous CH 4 measurements. One flight was selected for each of the three urban areas to quantify the emissions of N 2 O and CH 4 . Compared to the Dutch inventory, the estimated N 2 O emissions (364 ± 143 kg h -1 ) from the Rotterdam area are ∼3 times larger, whereas those for Groningen (95 ± 90 kg h -1 ) and Utrecht (32 ± 16 kg h -1 ) are not significantly different. The estimated CH 4 emissions for all three urban areas (Groningen: 2534 ± 1774 kg CH 4 hr -1 , Utrecht: 1440 ± 628 kg CH 4 hr -1 , and Rotterdam: 2419 ± 922 kg CH 4 hr -1 ) are not significantly different from the Dutch inventory. The innovative aircraft-based active AirCore sampling system provides a robust means of high-precision and continuous measurements of multiple gas species, which is useful for quantifying GHG emissions from urban areas.

After rotating a cylindrical tank containing a liquid at a constant rotation speed, by draining the liquid freely, an air-core phenomenon (that is, air is entrained into the drain port along a vortex flow) can be forcibly reproduced. This vortex phenomenon occurs very frequently in a variety of actual drainage situations and generally has a negative impact on many industrial devices, including reductions in drain speed, a noise and vibration, and structural damage of turbo machineries. The present study suggests a simple and very effective vortex-suppression device through physically analyzing the causes of the air-core phenomenon. In this study, liquid drainage processes with and without the suggested disc-type vortex suppressor were investigated numerically and experimentally. Through the numerical simulation, the internal flow characteristics have been investigated and the mechanism of the air-core formation has been revealed. As well, the experiments of varying the dimensions of the suggested disc-type vortex suppressor have been carried out. The velocity vector, drain water level, and vorticity distribution were compared for cases with and without the suggested vortex suppressor. [ABSTRACT FROM AUTHOR]

A mobile system was used for continuous ambient measurements of stable CH 4 isotopes ( 12 CH 4 and 13 CH 4 ) and ethane (C 2 H 6 ). This system was used during a winter mobile campaign to investigate the CH 4 isotopic signatures and the C 2 H 6 /CH 4 ratios of the main anthropogenic sources of CH 4 in the Canadian province of Alberta. Individual signatures were derived from δ 13 CH 4 and C 2 H 6 measurements in plumes arriving from identifiable single sources. Methane emissions from beef cattle feedlots (n = 2) and landfill (n = 1) had δ 13 CH 4 signatures of −66.7 ± 2.4‰ and −55.3 ± 0.2‰, respectively. The CH 4 emissions associated with the oil or gas industry had distinct δ 13 CH 4 signatures, depending on the formation process. Emissions from oil storage tanks (n = 5) had δ 13 CH 4 signatures ranging from −54.9 ± 2.9‰ to −60.6 ± 0.6‰ and non-detectable C 2 H 6 , characteristic of secondary microbial methanogenesis in oil-bearing reservoirs. In contrast, CH 4 emissions associated with natural gas facilities (n = 8) had δ 13 CH 4 signatures ranging from −41.7 ± 0.7‰ to −49.7 ± 0.7‰ and C 2 H 6 /CH 4 molar ratios of 0.10 for raw natural gas to 0.04 for processed/refined natural gas, consistent with thermogenic origins. These isotopic signatures and C 2 H 6 /CH 4 ratios have been used for source discrimination in the weekly atmospheric measurements of stable CH 4 isotopes over a two-month winter period at the Lac La Biche (LLB) measurement station, located in Alberta, approximately 200 km northeast of Edmonton. The average signature of −59.5 ± 1.4‰ observed at LLB is likely associated with transport of air after passing over oil industry sources located south of the station. [ABSTRACT FROM AUTHOR]

Draining of liquids through cylindrical tanks is a very common phenomenon and has many applications. Understanding the aircore formation and its growth during draining has attracted appreciable interest in the literature. In this study, water draining through cylindrical tanks was studied using experimental and numerical techniques. Eight different initial heights of water in the tank between 310 and 450 mm with a 20-mm increment were tested in each experiment. The numerical study shows good agreement with the experimental data and promotes understanding of the generation and disappearance of an aircore during draining. For the different initial water heights, the experiments were performed with and without initial rotation of the tank. It is found that in the experiments without initial tank rotation, the drain time of water increases with increasing initial height. On the other hand, the drain time remains almost the same for all initial heights tested with initial tank rotation. The small variation in the drain time even when the initial water level is reduced is explained by the aircore duration during draining. Also, the mechanism of generation and disappearance of aircore is proposed with the help of numerical results. [ABSTRACT FROM AUTHOR]

Enteric fermentation and manure methane emissions from livestock are major anthropogenic greenhouse gas emissions. In general, direct measurements of farm-scale methane emissions are scarce due to the source complexity and the limitations of existing atmospheric sampling methods. Using an innovative UAV-based active AirCore system, we have performed accurate atmospheric measurements of CH 4 mole fractions downwind of a dairy cow farm in the Netherlands on four individual days during the period from March 2017 to March 2019. The total CH 4 emission rates from the farm were determined using the UAV-based mass balance approach to be 1.1-2.4 g/s. After subtracting estimated emission factors of manure onsite, we derived the enteric emission factors to be 0.20-0.51 kgCH 4 /AU/d (1 AU = 500 kg animal weight) of dairy cows. We show that the uncertainties of the estimates were dominated by the variabilities in the wind speed and the angle between the wind and the flight transect. Furthermore, nonsimultaneous sampling in the vertical direction of the plume is one of the main limiting factors to achieving accurate estimate of the CH 4 emissions from the farm. In addition, a N 2 O tracer release experiment at the farm was performed when both a UAV and a mobile van were present to simultaneously sample the N 2 O tracer and the CH 4 plumes from the farm, improving the source quantification with a correction factor of 1.04 and 1.22 for the inverse Gaussian approach and for the mass balance approach, respectively. The UAV-based active AirCore system is capable of providing useful estimates of CH 4 emissions from dairy cow farms. The uncertainties of the estimates can be improved when combined with accurate measurements of local wind speed and direction or when combined with a tracer approach., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)