ORCID Profile
0000-0002-8535-0346
Current Organisation
Royal Holloway University of London
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Publisher: Copernicus GmbH
Date: 19-08-2016
DOI: 10.5194/ACP-16-10469-2016
Abstract: Abstract. High-precision analyses of the isotopic composition of methane in ambient air can potentially be used to discriminate between different source categories. Due to the complexity of isotope ratio measurements, such analyses have generally been performed in the laboratory on air s les collected in the field. This poses a limitation on the temporal resolution at which the isotopic composition can be monitored with reasonable logistical effort. Here we present the performance of a dual isotope ratio mass spectrometric system (IRMS) and a quantum cascade laser absorption spectroscopy (QCLAS)-based technique for in situ analysis of the isotopic composition of methane under field conditions. Both systems were deployed at the Cabauw Experimental Site for Atmospheric Research (CESAR) in the Netherlands and performed in situ, high-frequency (approx. hourly) measurements for a period of more than 5 months. The IRMS and QCLAS instruments were in excellent agreement with a slight systematic offset of (+0.25 ± 0.04) ‰ for δ13C and (−4.3 ± 0.4) ‰ for δD. This was corrected for, yielding a combined dataset with more than 2500 measurements of both δ13C and δD. The high-precision and high-temporal-resolution dataset not only reveals the overwhelming contribution of isotopically depleted agricultural CH4 emissions from ruminants at the Cabauw site but also allows the identification of specific events with elevated contributions from more enriched sources such as natural gas and landfills. The final dataset was compared to model calculations using the global model TM5 and the mesoscale model FLEXPART-COSMO. The results of both models agree better with the measurements when the TNO-MACC emission inventory is used in the models than when the EDGAR inventory is used. This suggests that high-resolution isotope measurements have the potential to further constrain the methane budget when they are performed at multiple sites that are representative for the entire European domain.
Publisher: Copernicus GmbH
Date: 14-09-2016
Publisher: Copernicus GmbH
Date: 10-02-2016
DOI: 10.5194/ACP-2016-60
Abstract: Abstract. High precision analyses of the isotopic composition of methane in ambient air can potentially be used to discriminate between different source categories. Due to the complexity of isotope ratio measurements, such analyses have generally been performed in the laboratory on air s les collected in the field. This poses a limitation on the temporal resolution at which the isotopic composition can be monitored with reasonable logistical effort. Here we present the performance of a dual isotope ratio mass spectrometric system (IRMS) and a quantum cascade laser absorption spectroscopy (QCLAS) based technique for in-situ analysis of the isotopic composition of methane under field conditions. Both systems were deployed at the Cabauw experimental site for atmospheric research (CESAR) in the Netherlands and performed in-situ, high-frequency (approx. hourly) measurements for a period of more than 5 months. The IRMS and QCLAS instruments were in excellent agreement with a slight systematic offset of +(0.05 ± 0.03) ‰ for δ13C and –(3.6 ± 0.4) ‰ for δD. This was corrected for, yielding a combined dataset with more than 2500 measurements of both δ13C and δD. The high precision and temporal resolution dataset does not only reveal the overwhelming contribution of isotopically depleted agricultural CH4 emissions from ruminants at the Cabauw site, but also allows the identification of specific events with elevated contributions from more enriched sources such as natural gas and landfills. The final dataset was compared to model calculations using the global model TM5 and the mesoscale model FLEXPART-COSMO. The results of both models agree better with the measurements when the TNO-MACC emission inventory is used in the models than when the EDGAR inventory is used. This suggests that high-resolution isotope measurements have the potential to further constrain the methane budget, when they are performed at multiple sites that are representative for the entire European domain.
Publisher: Copernicus GmbH
Date: 27-01-2016
Abstract: Abstract. In situ and simultaneous measurement of the three most abundant isotopologues of methane using mid-infrared laser absorption spectroscopy is demonstrated. A field-deployable, autonomous platform is realized by coupling a compact quantum cascade laser absorption spectrometer (QCLAS) to a preconcentration unit, called trace gas extractor (TREX). This unit enhances CH4 mole fractions by a factor of up to 500 above ambient levels and quantitatively separates interfering trace gases such as N2O and CO2. The analytical precision of the QCLAS isotope measurement on the preconcentrated (750 ppm, parts-per-million, µmole mole−1) methane is 0.1 and 0.5 ‰ for δ13C- and δD-CH4 at 10 min averaging time. Based on repeated measurements of compressed air during a 2-week intercomparison c aign, the repeatability of the TREX–QCLAS was determined to be 0.19 and 1.9 ‰ for δ13C and δD-CH4, respectively. In this intercomparison c aign the new in situ technique is compared to isotope-ratio mass spectrometry (IRMS) based on glass flask and bag s ling and real time CH4 isotope analysis by two commercially available laser spectrometers. Both laser-based analyzers were limited to methane mole fraction and δ13C-CH4 analysis, and only one of them, a cavity ring down spectrometer, was capable to deliver meaningful data for the isotopic composition. After correcting for scale offsets, the average difference between TREX–QCLAS data and bag/flask s ling–IRMS values are within the extended WMO compatibility goals of 0.2 and 5 ‰ for δ13C- and δD-CH4, respectively. This also displays the potential to improve the interlaboratory compatibility based on the analysis of a reference air s le with accurately determined isotopic composition.
Publisher: Copernicus GmbH
Date: 10-12-2014
DOI: 10.5194/ACP-14-13159-2014
Abstract: Abstract. Airborne and ground-based measurements of methane (CH4), carbon dioxide (CO2) and boundary layer thermodynamics were recorded over the Fennoscandian landscape (67–69.5° N, 20–28° E) in July 2012 as part of the MAMM (Methane and other greenhouse gases in the Arctic: Measurements, process studies and Modelling) field c aign. Employing these airborne measurements and a simple boundary layer box model, net regional-scale (~ 100 km) fluxes were calculated to be 1.2 ± 0.5 mg CH4 h−1 m−2 and −350 ± 143 mg CO2 h−1 m−2. These airborne fluxes were found to be relatively consistent with seasonally averaged surface chamber (1.3 ± 1.0 mg CH4 h−1 m−2) and eddy covariance (1.3 ± 0.3 mg CH4 h−1 m−2 and −309 ± 306 mg CO2 h−1 m−2) flux measurements in the local area. The internal consistency of the aircraft-derived fluxes across a wide swath of Fennoscandia coupled with an excellent statistical comparison with local seasonally averaged ground-based measurements demonstrates the potential scalability of such localised measurements to regional-scale representativeness. Comparisons were also made to longer-term regional CH4 climatologies from the JULES (Joint UK Land Environment Simulator) and HYBRID8 land surface models within the area of the MAMM c aign. The average hourly emission flux output for the summer period (July–August) for the year 2012 was 0.084 mg CH4 h−1 m−2 (minimum 0.0 and maximum 0.21 mg CH4 h−1 m−2) for the JULES model and 0.088 mg CH4 h−1 m−2 (minimum 0.0008 and maximum 1.53 mg CH4 h−1 m−2) for HYBRID8. Based on these observations both models were found to significantly underestimate the CH4 emission flux in this region, which was linked to the under-prediction of the wetland extents generated by the models.
Publisher: American Geophysical Union (AGU)
Date: 13-12-2016
DOI: 10.1002/2016JD026006
Publisher: Elsevier BV
Date: 05-2008
Publisher: Elsevier BV
Date: 12-2008
Publisher: Copernicus GmbH
Date: 31-08-2015
Abstract: Abstract. In situ and simultaneous measurement of the three most abundant isotopologues of methane using mid-infrared laser absorption spectroscopy is demonstrated. A field-deployable, autonomous platform is realized by coupling a compact quantum cascade laser absorption spectrometer (QCLAS) to a preconcentration unit, called TRace gas EXtractor (TREX). This unit enhances CH4 mole fractions by a factor of up to 500 above ambient levels and quantitatively separates interfering trace gases such as N2O and CO2. The analytical precision of the QCLAS isotope measurement on the preconcentrated (750 ppm, parts-per-million, μmole/mole) methane is 0.1 and 0.5 ‰ for δ13C- and δD-CH4 at 10 min averaging time. Based on replicate measurements of compressed air during a two-week intercomparison c aign, the repeatability of the TREX-QCLAS was determined to be 0.19 and 1.9 ‰ for δ13C and δD-CH4, respectively. In this intercomparison c aign the new in situ technique is compared to isotope-ratio mass-spectrometry (IRMS) based on glass flask and bag s ling and real time CH4 isotope analysis by two commercially available laser spectrometers. Both laser-based analyzers were limited to methane mole fraction and δ13C-CH4 analysis, and only one of them, a cavity ring down spectrometer, was capable to deliver meaningful data for the isotopic composition. After correcting for scale offsets, the average difference between TREX–QCLAS data and bag/flask s ling–IRMS values are within the extended WMO compatibility goals of 0.2 and 5 ‰ for δ13C- and δD-CH4, respectively. Thus, the intercomparison also reveals the need for reference air s les with accurately determined isotopic composition of CH4 to further improve the interlaboratory compatibility.
Publisher: Springer Science and Business Media LLC
Date: 04-11-2015
DOI: 10.1038/SREP15996
Abstract: Coal seam gas (CSG) production can have an impact on groundwater quality and quantity in adjacent or overlying aquifers. To assess this impact we need to determine the background groundwater chemistry and to map geological pathways of hydraulic connectivity between aquifers. In south-east Queensland (Qld), Australia, a globally important CSG exploration and production province, we mapped hydraulic connectivity between the Walloon Coal Measures (WCM, the target formation for gas production) and the overlying Condamine River Alluvial Aquifer (CRAA), using groundwater methane (CH 4 ) concentration and isotopic composition (δ 13 C-CH 4 ), groundwater tritium ( 3 H) and dissolved organic carbon (DOC) concentration. A continuous mobile CH 4 survey adjacent to CSG developments was used to determine the source signature of CH 4 derived from the WCM. Trends in groundwater δ 13 C-CH 4 versus CH 4 concentration, in association with DOC concentration and 3 H analysis, identify locations where CH 4 in the groundwater of the CRAA most likely originates from the WCM. The methodology is widely applicable in unconventional gas development regions worldwide for providing an early indicator of geological pathways of hydraulic connectivity.
Publisher: Copernicus GmbH
Date: 03-11-2016
DOI: 10.5194/ACP-16-13669-2016
Abstract: Abstract. Currently, the atmospheric methane burden is rising rapidly, but the extent to which shifts in coal production contribute to this rise is not known. Coalbed methane emissions into the atmosphere are poorly characterised, and this study provides representative δ13CCH4 signatures of methane emissions from specific coalfields. Integrated methane emissions from both underground and opencast coal mines in the UK, Australia and Poland were s led and isotopically characterised. Progression in coal rank and secondary biogenic production of methane due to incursion of water are suggested as the processes affecting the isotopic composition of coal-derived methane. An averaged value of −65 ‰ has been assigned to bituminous coal exploited in open cast mines and of −55 ‰ in deep mines, whereas values of −40 and −30 ‰ can be allocated to anthracite opencast and deep mines respectively. However, the isotopic signatures that are included in global atmospheric modelling of coal emissions should be region- or nation-specific, as greater detail is needed, given the wide global variation in coal type.
Publisher: Copernicus GmbH
Date: 12-12-2022
DOI: 10.5194/ACP-22-15527-2022
Abstract: Abstract. In-flight measurements of atmospheric methane (CH4(a)) and mass balance flux quantification studies can assist with verification and improvement in the UNFCCC National Inventory reported CH4 emissions. In the Surat Basin gas fields, Queensland, Australia, coal seam gas (CSG) production and cattle farming are two of the major sources of CH4 emissions into the atmosphere. Because of the rapid mixing of adjacent plumes within the convective boundary layer, spatially attributing CH4(a) mole fraction readings to one or more emission sources is difficult. The primary aims of this study were to use the CH4(a) isotopic composition (δ13CCH4(a)) of in-flight atmospheric air (IFAA) s les to assess where the bottom–up (BU) inventory developed specifically for the region was well characterised and to identify gaps in the BU inventory (missing sources or over- and underestimated source categories). Secondary aims were to investigate whether IFAA s les collected downwind of predominantly similar inventory sources were useable for characterising the isotopic signature of CH4 sources (δ13CCH4(s)) and to identify mitigation opportunities. IFAA s les were collected between 100–350 m above ground level (m a.g.l.) over a 2-week period in September 2018. For each IFAA s le the 2 h back-trajectory footprint area was determined using the NOAA HYSPLIT atmospheric trajectory modelling application. IFAA s les were gathered into sets, where the 2 h upwind BU inventory had 50 % attributable to a single predominant CH4 source (CSG, grazing cattle, or cattle feedlots). Keeling models were globally fitted to these sets using multiple regression with shared parameters (background-air CH4(b) and δ13CCH4(b)). For IFAA s les collected from 250–350 m a.g.l. altitude, the best-fit δ13CCH4(s) signatures compare well with the ground observation: CSG δ13CCH4(s) of −55.4 ‰ (confidence interval (CI) 95 % ± 13.7 ‰) versus δ13CCH4(s) of −56.7 ‰ to −45.6 ‰ grazing cattle δ13CCH4(s) of −60.5 ‰ (CI 95 % ± 15.6 ‰) versus −61.7 ‰ to −57.5 ‰. For cattle feedlots, the derived δ13CCH4(s) (−69.6 ‰, CI 95 % ± 22.6 ‰), was isotopically lighter than the ground-based study (δ13CCH4(s) from −65.2 ‰ to −60.3 ‰) but within agreement given the large uncertainty for this source. For IFAA s les collected between 100–200 m a.g.l. the δ13CCH4(s) signature for the CSG set (−65.4 ‰, CI 95 % ± 13.3 ‰) was isotopically lighter than expected, suggesting a BU inventory knowledge gap or the need to extend the population statistics for CSG δ13CCH4(s) signatures. For the 100–200 m a.g.l. set collected over grazing cattle districts the δ13CCH4(s) signature (−53.8 ‰, CI 95 % ± 17.4 ‰) was heavier than expected from the BU inventory. An isotopically light set had a low δ13CCH4(s) signature of −80.2 ‰ (CI 95 % ± 4.7 ‰). A CH4 source with this low δ13CCH4(s) signature has not been incorporated into existing BU inventories for the region. Possible sources include termites and CSG brine ponds. If the excess emissions are from the brine ponds, they can potentially be mitigated. It is concluded that in-flight atmospheric δ13CCH4(a) measurements used in conjunction with endmember mixing modelling of CH4 sources are powerful tools for BU inventory verification.
Publisher: American Geophysical Union (AGU)
Date: 19-07-2017
DOI: 10.1002/2017JD026626
Publisher: Copernicus GmbH
Date: 31-03-2014
DOI: 10.5194/ACPD-14-8455-2014
Abstract: Abstract. Airborne and ground-based measurements of methane (CH4), carbon dioxide (CO2) and boundary layer thermodynamics were recorded over the Fennoscandian wetlands in July 2012 as part of the MAMM (Methane and other greenhouse gases in the Arctic – Measurements, process studies and Modelling) field c aign. Employing these airborne measurements and a~simple boundary layer box model, net regional scale (~100 km) fluxes were calculated to be 1.2 ± 0.5 mg CH4 h−1 m−2 and −350 ± 143 mg CO2 h−1 m−2. These airborne fluxes were found to be relatively consistent with seasonally-averaged surface chamber (1.3 ± 1.0 mg CH4 h−1 m−2) and eddy covariance (1.3 ± 0.3 mg CH4 h−1 m−2 and −309 ± 306 mg CO2 h−1 m−2) flux measurements in the local area. The internal consistency of the aircraft-derived fluxes across a wide swath of Fennoscandia coupled with an excellent statistical comparison with local seasonally-averaged ground-based measurements demonstrates the potential scalability of such localised measurements to regional scale representivity. Comparisons were also made to longer term regional CH4 climatologies from the JULES (Joint UK Land Environment Simulator) and Hybrid8 land surface models within the area of the MAMM c aign. The average hourly emission flux output for the summer period (July–August) across the years 1980 to 2010 was 0.054 mg CH4 h−1 m−2 (minimum 0.0 and maximum 0.38 mg CH4 h−1 m−2) for the JULES model and 0.073 mg CH4 h−1 m−2 (minimum −0.0018 and maximum 4.62 mg CH4 h−1 m−2) for Hybrid8. Based on these observations both models were found to significantly underestimate the CH4 emission flux in this region, which was linked to the under prediction of the wetland extents generated by the models.
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for DAVID LOWRY.