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

Abstract

Abstract. Methane (CH4) emissions from human activities are a threat to the resilience of our current climate system. The stable isotopic composition of methane (δ13C and δ2H) allows us to distinguish between the different CH4 origins. A significant part of the European CH4 emissions, 3.6 % in 2018, comes from coal extraction in Poland, the Upper Silesian Coal Basin (USCB) being the main hotspot. Measurements of CH4 mole fraction (χ(CH4)), δ13C, and δ2H in CH4 in ambient air were performed continuously during 6 months in 2018 and 2019 at Krakow, Poland, in the east of the USCB. In addition, air samples were collected during parallel mobile campaigns, from multiple CH4 sources in the footprint area of the continuous measurements. The resulting isotopic signatures from sampled plumes allowed us to distinguish between natural gas leaks, coal mine fugitive emissions, landfill and sewage, and ruminants. The use of δ2H in CH4 is crucial to distinguish the fossil fuel emissions in the case of Krakow because their relatively depleted δ13C values overlap with the ones of microbial sources. The observed χ(CH4) time series showed regular daily night-time accumulations, sometimes combined with irregular pollution events during the day. The isotopic signatures of each peak were obtained using the Keeling plot method and generally fall in the range of thermogenic CH4 formation – with δ13C between −59.3 ‰ and −37.4 ‰ Vienna Pee Dee Belemnite (V-PDB) and δ2H between −291 ‰ and −137 ‰ Vienna Standard Mean Ocean Water (V-SMOW). They compare well with the signatures measured for gas leaks in Krakow and USCB mines. The CHIMERE transport model was used to compute the CH4 and isotopic composition time series in Krakow, based on two emission inventories. The magnitude of the pollution events is generally underestimated in the model, which suggests that emission rates in the inventories are too low. The simulated isotopic source signatures, obtained with Keeling plots on each simulated peak, indicate that a higher contribution from fuel combustion sources in the EDGAR v5.0 inventory would lead to a better agreement than when using CAMS-REG-GHG v4.2 (Copernicus Atmosphere Monitoring Service REGional inventory for Air Pollutants and GreenHouse Gases). The isotopic mismatches between model and observations are mainly caused by uncertainties in the assigned isotopic signatures for each source category and the way they are classified in the inventory. These uncertainties are larger for emissions close to the study site, which are more heterogenous than the ones advected from the USCB coal mines. Our isotope approach proves to be very sensitive in this region, thus helping to evaluate emission estimates.

Observational constraints on methane emissions from Polish coal mines using a ground-based remote sensing network

“…than Za Miastem on 7 June. Thus, the background concentration field has some spatial variability which might be connected to remote sources such as the Krakow urban region affecting The Glade but not Za Miastem (Menoud et al, 2021). In the future, we will aim at estimating errors due to spatial background variability by running a model that includes all known sources in a larger area around the target region or by deploying more spectrometers.…”

“…Using airborne imager data, Krautwurst et al (2021) found some discrepancies between their estimates and the E-PRTR inventory for small groups of ventilation facilities. The isotopic CH 4 composition was measured by Menoud et al (2021) with ground-based in situ instruments. Swolkień (2020) discusses the short-term, shaft-wise CH 4 release in the USCB.…”

Local to regional methane emissions from the Upper Silesia Coal Basin (USCB) quantified using UAV-based atmospheric measurements

“…The isotopic composition was determined by analyzing the samples stored in the Tedlar bags using a continuous flow isotope ratio mass spectrometer system. More details about the analytical system and the calibration are provided in Brass and Röckmann, 2011;Röckmann et al, 2016;Menoud et al, 2021. Out of the 59 flights performed during this study, the air samples from 34 flights were stored in Tedlar bags for further analysis of isotopic composition.…”

Assessment of GHG Interactions in the Vicinity of the Municipal Waste Landfill Site—Case Study

“…It is still difficult to assess the scale of CO 2 and CH 4 emissions from landfill facilities due to the large temporal and spatial variations in the landfill source strength [7,19,20]. The combination of high-resolution atmospheric and precise stable isotope measurements acts as an effective tool for monitoring the strength of major CO 2 and CH 4 sources and understanding GHGs biogeochemistry [21][22][23][24][25]. The ranges of isotopic signatures (δ 13 C) of carbon dioxide and methane emitted from the major source categories are very large.…”

“…The ranges of isotopic signatures (δ 13 C) of carbon dioxide and methane emitted from the major source categories are very large. With respect to carbon isotopic fractionation during methanogenesis, three types of methane sources have distinct δ 13 C signatures, whereby biogenic CH 4 is heavily depleted in 13 C (from −75 to −55‰) [26,27] whereas thermogenic methane typically has δ 13 C values (from −60 to −20‰) [28,29] and pyrogenic methane is assigned more enriched values (−50 to −40‰) [21,30]. The isotopic range of δ 13 C(CO 2 ) for terrestrial vegetation varies from −29 to −12‰ [31,32] whereas the δ 13 C composition of fossil fuel combustion ranges from −44‰ to −22‰ [22,33].…”