In situ observations of greenhouse gases over Europe during the CoMet 1.0 campaign aboard the HALO aircraft

Abstract

Abstract. The intensive measurement campaign CoMet 1.0 (Carbon dioxide and Methane mission) took place during May and June 2018, with a focus on greenhouse gases over Europe. CoMet 1.0 aimed at characterising the distribution of CH4 and CO2 over significant regional sources with the use of a fleet of research aircraft, as well as validating remote sensing measurements from state-of-the-art instrumentation installed on-board against a set of independent in-situ observations. Here we present the results of over 55 hours of accurate and precise in situ measurements of CO2, CH4 and CO mixing ratios made during CoMet 1.0 flights with a cavity ring-down spectrometer aboard the German research aircraft HALO, together with results from analyses of 96 discrete air samples collected aboard the same platform. A careful in-flight calibration strategy together with post-flight quality assessment made it possible to determine both the single measurement precision as well as biases against respective WMO scales. We compare the result of greenhouse gas observations against two of the available global modelling systems, namely Jena CarboScope and CAMS (Copernicus Atmosphere Monitoring Service). We find overall good agreement between the global models and the observed mixing ratios in the free-tropospheric range, characterised by very low bias values for the CAMS CH4 and the CarboScope CO2 products, with a mean free tropospheric offset of 0 (14) ppb and 0.8 (1.3) ppm respectively, with the quoted number giving the standard uncertainty in the final digits for the numerical value. Higher bias is observed for CAMS CO2 (equal to 3.7 (1.5) ppm), and for CO the model-observation mismatch is variable with height (with offset equal to −1.0 (8.8)). We also present laboratory analyses of air samples collected throughout the flights, which include information on the isotopic composition of CH_4, and we demonstrate the potential of simultaneously measuring δ13C-CH4 and δ2H-CH4 from air to determine the sources of enhanced methane signals using even a limited amount of discrete samples. Using flasks collected during two flights over the Upper Silesian Coal Basin (USCB, southern Poland), one of the strongest methane-emitting regions in the European Union, we were able to use the Miller-Tans approach to derive the isotopic signature of the measured source, with values of δ2H equal to −224.7 (6.6) permil and δ13C to −50.9 (1.1) permil, giving significantly lower d2H values compared to previous studies in the area.

Determination of the Emission Rates of CO<sub>2</sub> Point Sources with Airborne Lidar

“…The CoMet campaign saw the deployment of a suite of the most sophisticated airborne instruments to measure atmospheric CH4 and CO2, as well as a variety of ground-based instruments. In particular, also the synergetic use of active remote sensing (lidar) (Amediek et al, 2017;Wildmann et al, 2020), passive spectrometry (Luther et al, 2019;Krings et al, 2011), and in situ measurements (Fiehn et al, 2020;Gałkowski et al, 2020) supported by modelling activities (Chen et al, 2020;Nickl et al, 2020), as well as the validation of existing (e.g. Sentinel-5P, GOSAT (Greenhouse Gases Observing Satellite)) and the preparation of upcoming (e.g.…”

Measurement report: Methane (CH<sub>4</sub>) sources in Krakow, Poland: insights from isotope analysis

“…The Upper Silesian Coal Basin (USCB), where most mining activity occurs in Poland, is certainly a CH 4 emission hotspot in Europe. Atmospheric measurements at the USCB were mostly performed in the recent years (Swolkień (2020), Luther et al (2019), Gałkowski et al (2020), Fiehn et al (2020)), and focused on the coal extraction activities. The area covered by the USCB includes other sources of methane, such as ruminant farming and waste degradation.…”