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

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From: Atmospheric Chemistry and Physics(Vol. 21, Issue 17)
Publisher: Copernicus GmbH
Document Type: Article
Length: 488 words

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Abstract :

Methane (CH.sub.4) emissions from human activities are a threat to the resilience of our current climate system. The stable isotopic composition of methane ([delta].sup.13 C and [delta].sup.2 H) allows us to distinguish between the different CH.sub.4 origins. A significant part of the European CH.sub.4 emissions, 3.6 % in 2018, comes from coal extraction in Poland, the Upper Silesian Coal Basin (USCB) being the main hotspot. Measurements of CH.sub.4 mole fraction (Ï(CH.sub.4 )), [delta].sup.13 C, and [delta].sup.2 H in CH.sub.4 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 CH.sub.4 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 [delta].sup.2 H in CH.sub.4 is crucial to distinguish the fossil fuel emissions in the case of Krakow because their relatively depleted [delta].sup.13 C values overlap with the ones of microbial sources. The observed Ï(CH.sub.4) 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 CH.sub.4 formation - with [delta].sup.13 C between -59.3 0/00 and -37.4 0/00 Vienna Pee Dee Belemnite (V-PDB) and [delta].sup.2 H between -291 0/00 and -137 0/00 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 CH.sub.4 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.

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Gale Document Number: GALE|A674494182