A simultaneous CH4 and CO2 flux quantification method for industrial site emissions from in-situ concentration measurements on-board an Unmanned Aircraft Vehicle
Abstract. We developed an innovative tool to quantify CO2 and CH4 emissions at the scale of an industrial site, based on a mass balance approach relying on a newly developed light-weight (1.4 kg) open path laser absorption spectrometer operable on-board Unmanned Aircraft Vehicles (UAVs). This spectrometer simultaneously records in situ CO2 and CH4 concentrations at high frequency (24 Hz in this study) with precisions of 10 ppb for CH4 and 1 ppm for CO2 averaged at 1 Hz. The large range of measurable concentrations, up to 1000 ppm for CO2 and 200 ppm for CH4, makes this analyzer suitable for operation on industrial sites at a short distance from the emission sources, therefore avoiding many logistical and legal limits associated with most long-range airborne observations. To quantify the emissions, high spatial resolution atmospheric concentration measurements obtained throughout a plume cross-section downwind of a source within the limited UAV flight period are exploited by calculations using a mass balance approach. This high spatial resolution, allowed by the high acquisition frequency, limits the use of horizontal interpolation, thus gaining in precision compared to current airborne alternative quantification techniques.
A field validation campaign, conducted on the TotalEnergies TADI test platform at Lacq, France, consisted in controlled CO2 and CH4 leak experiments to which several institutes participated with various measurement systems (gas LiDAR, multispectral camera, infrared camera including concentrations and emissions quantification system, acoustic sensors, ground mobile and fixed Cavity RingDown Spectrometers). Our method was proved suitable to detect leaks during controlled release experiments with emission fluxes down to 0.01 g s−1, with 24 % of estimated CH4 fluxes within the −20 % to +20 % error range, 80 % of quantifications within the −50 % to +100 % error range and all of our results within the −69 % to +150 % error range. Such precision levels are better ranked than current top-down alternative techniques to quantify CH4 at comparable spatial scales.
Observations across the plume of two offshore oil and gas platforms operated by TotalEnergies in the North Sea were used to quantify the instantaneous greenhouse gases emissions of these facilities and are coherent with reference emissions for these platforms estimated by mass balance and combustion calculations for CO2. The operational deployment of such instruments and quantification methods, on a large scale and on a regular basis, potentially with fully autonomous UAVs, will allow the quantification of the time dependent greenhouse gases emissions of numerous oil and gas facilities.
Jean-Louis Bonne et al.
Status: open (extended)
- RC1: 'Comment on amt-2022-334', Anonymous Referee #1, 03 Jun 2023 reply
Jean-Louis Bonne et al.
Jean-Louis Bonne et al.
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Bonne et al., presented a new light-weight open path laser absorption spectrometer for in situ CO2 and CH4 concentration measurements, and applied the analyzer in the fields to quantify the emission rates of a series of controlled releases of CH4 and CO2 at the TotalEnergies TADI test platform at Lacq, France and of two offshore oil and gas platforms in the North Sea. Gas LiDAR was used to obtain vertical profiles of wind speeds and directions on site, which were used in the mass balance approach to calculate the emission rates. The paper is well structured, and both the laboratory and field experiments results could be useful to further develop the application of quantification of greenhouse gas emissions using UAVs. On the other hand, the paper would have benefited from more stringent discussion of the uncertainties of the measurements and the quantification using the mass balance approach. The paper is suitable for publication after addressing my following concerns.
Some detailed comments:
L11-37: the abstract can be written more concisely.
L145: still, some more brief description of the system will be appreciated, e.g., how temperature and pressure variations are taken into account. How is water vapor used? How is the spectra data used to derive the mole fractions?
L246: Similar flight protocols have been presented earlier, e.g., in Andersen et al., 2021, and Morles et al., 2022. Also, a minimum wind speed was used to select appropriate flights for analyses. How was the wind speed considered in this paper?
L249: under the wind should be downwind
L270: what is the unit of Cp? Note that the water vapor effect needs to be considered, as is in eq. (4) in Andersen et al., 2021.
L337: plan should be plane
Andersen, T., Vinkovic, K., Vries, M.d., Kers,B., Necki, J., Swolkien, J., Roiger, A., Peters, W., Chen, H.:Quantifying methane emissions from coal mining ventilation shafts using an unmanned aerial vehicle (UAV)-based active AirCore system, Atmos. Environ.: X, Volume 12, 100135, ISSN 2590-1621, https://doi.org/10.1016/j.aeaoa.2021.100135, 2021.