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Methane stable isotope analysis, coupled with mole fraction measurement, has been used to link isotopic signature to methane emissions from landfill sites, coal mines and gas leaks in the United Kingdom. A mobile Picarro G2301 CRDS (Cavity Ring-Down Spectroscopy) analyser was installed on a vehicle, together with an anemometer and GPS receiver, to measure atmospheric methane mole fractions and their relative location while driving at speeds up to 80 kph. In targeted areas, when the methane plume was intercepted, air samples were collected in Tedlar bags, for δ 13 C–CH 4 isotopic analysis by CF-GC-IRMS (Continuous Flow Gas Chromatography-Isotope Ratio Mass Spectrometry). This method provides high precision isotopic values, determining δ 13 C–CH 4 to ±0.05 per mil. The bulk signature of the methane plume into the atmosphere from the whole source area was obtained by Keeling plot analysis, and a δ 13 C–CH 4 signature, with the relative uncertainty, allocated to each methane source investigated. Both landfill and natural gas emissions in SE England have tightly constrained isotopic signatures. The averaged δ 13 C–CH 4 for landfill sites is −58 ± 3‰. The δ 13 C–CH 4 signature for gas leaks is also fairly constant around −36 ± 2‰, a value characteristic of homogenised North Sea supply. In contrast, signatures for coal mines in N. England and Wales fall in a range of −51.2 ± 0.3‰ to −30.9 ± 1.4‰, but can be tightly constrained by region. The study demonstrates that CRDS-based mobile methane measurement coupled with off-line high precision isotopic analysis of plume samples is an efficient way of characterising methane sources. It shows that isotopic measurements allow type identification, and possible location of previously unknown methane sources. In modelling studies this measurement provides an independent constraint to determine the contributions of different sources to the regional methane budget and in the verification of inventory source distribution. [ABSTRACT FROM AUTHOR]

The distribution of methane sources in Kuwait was mapped through mobile vehicle surveying of methane mole fraction, and by collection of air samples at source for subsequent isotopic analysis. Mobile plume identification and isotopic analysis, reveals that by far the largest observed source of methane in Kuwait is from landfill sites (δ13C CH4 of −58‰), with smaller contributions from fossil fuel industry (−50‰), wastewater treatment (−49‰) and ruminant animals (sheep −64‰, cows, −62‰, camels −60‰). Regular weekly air samples were collected over two years from three sites in Kuwait, one NW of the city, one to the SE and one in the city from the rooftop of the Kuwait College of Science. Associated with higher mole fraction is a consistent depletion in 13C of methane, pointing to a national source mix with δ13C CH4 of −55.9‰. This is significantly different from calculations using EDGAR v.5 inventory that suggest a source mix of −52.8‰. Diurnal campaigns from a city location confirm that the sources are dominantly biogenic (−59 to −56‰) in and around the urban areas. The EDGAR 5.0 inventory suggests that the dominant sources of methane in Kuwait are leaks from gas flaring and fossil fuel distribution, with additional smaller emissions from landfills, sewage (wastewater) treatment and ruminant animals, but with a waste component increasing relative to fossil fuel emissions in recent decades. Measurements during 2015 and 2016 suggest that for all but the far south and SW of the country which is not in the meteorological footprint of fixed site or mobile measurement, there is a dominant waste source and much smaller observed proportion from fossil fuel activities. This research demonstrates for the first time in Kuwait that continuous mobile measurements for plume identification coupled with high-precision isotopic analysis using CF-GC-IRMS (Continuous Flow Gas Chromatography-Isotope Ratio Mass Spectrometry) is an effective way of identifying methane sources and understanding their relative contributions. To unambiguously quantify relative contributions will require further work, particularly in the SW region of the country, utilizing aircraft and/or satellite retrievals. The results of this research will contribute to understanding the methane budget of this poorly studied region. [Display omitted] • Weekly sampling and methane isotopic analysis for 3 Kuwait sites over 2 years. • Mobile CH 4 measurement campaign for 7 days with subsequent GIS mapping. • Characterization of methane sources into fossil fuel, waste and ruminant categories. • Diurnal sampling in Kuwait City suburb identifies landfill as main methane source. • Isotopes identify waste as main source, not fossil fuels as in EDGAR inventory. [ABSTRACT FROM AUTHOR]

Measurements of the stable isotopic composition ( δ D(H 2 ) or δ D) of atmospheric molecular hydrogen (H 2 ) are a useful addition to mixing ratio ( χ (H 2 )) measurements for understanding the atmospheric H 2 cycle. δ D datasets published so far consist mostly of observations at background locations. We complement these with observations from the Cabauw tall tower at the CESAR site, situated in a densely populated region of the Netherlands. Our measurements show a large anthropogenic influence on the local H 2 cycle, with frequently occurring pollution events that are characterized by χ (H 2 ) values that reach up to ≈1 ppm and low δ D values. An isotopic source signature analysis yields an apparent source signature below −400‰, which is much more D-depleted than the fossil fuel combustion source signature commonly used in H 2 budget studies. Two diurnal cycles that were sampled at a suburban site near London also show a more D-depleted source signature (≈−340‰), though not as extremely depleted as at Cabauw. The source signature of the Northwest European vehicle fleet may have shifted to somewhat lower values due to changes in vehicle technology and driving conditions. Even so, the surprisingly depleted apparent source signature at Cabauw requires additional explanation; microbial H 2 production seems the most likely cause. The Cabauw tower site also allowed us to sample vertical profiles . We found no decrease in χ (H 2 ) at lower sampling levels (20 and 60 m) with respect to higher sampling levels (120 and 200 m). There was a significant shift to lower median δ D values at the lower levels. This confirms the limited role of soil uptake around Cabauw, and again points to microbial H 2 production during an extended growing season, as well as to possible differences in average fossil fuel combustion source signature between the different footprint areas of the sampling levels. So, although knowledge of the background cycle of H 2 has improved over the last decade, surprising features come to light when a non-background location is studied, revealing remaining gaps in our understanding. [ABSTRACT FROM AUTHOR]