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One of the case study sites for the Climate and Clean Air Coalition (CCAC) Methane Science Studies is the coal seam gas (CSG) field in the Surat Basin, Queensland, Australia, where there are over 6000 CSG wells and associated gas and water processing infrastructure. Previous bottom-up estimates suggest that the major source of methane in the region is cattle, not CSG (Katestone, 2018, Luhar et al. 2018).In September 2018, an airborne measurement campaign was undertaken to provide a top-down estimate of regional methane emissions. Modelling of the airborne methane mole fraction data has produced a defensible total methane emissions estimate. However, there are challenges with proportioning the top-down estimates provided by the airborne data, because of adjacent sources with similar d13C-CH4 isotopic chemistry, rapid mixing of adjacent sources and substantial dilution of the plumes at the airborne measurement sampling height. We present how we will overcome these challenges.At each gas production well, tens of thousands of litres of water are produced daily in association with the methane extracted from the coal measures. This water is stored in ponds and is also used as a water supply for cattle feedlots, which are located throughout and adjacent to the CSG wells and processing facilities. Power stations are also located within the CSG field. This arrangement makes it challenging to obtain clean top-down estimates of the emissions from CSG production. Quantifying methane emissions associated with CSG production is further complicated by numerous other sources of methane in the region immediately adjacent to the CSG field. These sources include grazing cattle, abattoirs, more power production facilities, coal mines, wetlands, natural gas seeps, and small urban centres with associated sewage treatment plants and landfills. Grab bag air samples were collected at each of these sources and analysed for d13C-CH4, d13C-CO2 and dD-CH4.The airborne measurement campaign was u

Melbourne was founded in 1835 and has grown to become Australia’s second most populous city with a populationof almost 5 million people [ABS, 2019]. As Melbourne’s population has expanded, land use and infrastructure haschanged many times and this has resulted in a variety of potential methane (CH4) sources, such as legacy and newlandfills, leaks from the gas distribution and sewage networks, and houses with a range of heating systems includinggas and wood fires. There are also large wetland areas and coastal ecosystems. Few of these potential sources ofCH4 have been well characterised. Here we present the results of 500 km of mobile methane surveying throughoutthe south-eastern suburbs of Melbourne, during day and night time, that mapped the location of major CH4 sourcesin July 2019. Where major plumes could be attributed to a source based on proximity or smell (for example adomestic distribution gas leak or wood burning fire) the δ13C_CH4 (isotopic signature) of that source wascharacterised.The methane mole fraction ([CH4]) was measured using a Los Gatos Research (LGR) greenhouse gas analyserthat was placed within the car. The air intake was mounted on the roof of the car approximately 2.5 m above theground, and the air was drawn into the analyser via a Teflon tube. The CH4 data were geopositioned using aHemisphere (model A21) GPS unit and all the results were converted to kml files for displaying in Google Earth. Foreach major plume 10 air samples were collected in SKC FlexFoil bags and later analysed for [CH4], δ13C_CH4, [CO2]and δ13C_CO2 using a Picarro G2201-i cavity ring-down spectrometer (CRDS) at the UNSW Sydney greenhouse gaslaboratory. To determine the plume CH4 source signature the ten sample {[CH4], δ13C_CH4} sets were then analysedusing Bayesian regression in Miller-Tans plot [Miller and Tans, 2003].The measured mole fractions of methane ([CH4]) ranged from 1.83 ppm to 147 ppm (associated with gas leak ina residential area). Our preliminary results ind

To characterise the isotopic chemistry of a source it is common to collect three or more grab bag samples of air from the plume downwind of the source of interest. Each air sample is then transported to a laboratory for precise analysis of the concentration and isotopic chemistry for the molecule of interest. The isotopic signature of the source is then determined by analysing the composition data in a Keeling or Miller-Tans plot (Keeling, 1961; Miller and Tans, 2003), which provides only a single estimate of the isotopic source signature. However, there is often considerable variability within the same source category, both at a single sample site and more commonly between sites. Ideally, the variability in the source category isotopic signature needs to be characterised for subsequent use in modelling blended regional-scale isotopic signatures. Another positive aspect of the in-field time series data sets is the real-time feedback, which may assist with refining sampling strategies.Laser spectrometers enable the collection of in situ time series data for both the concentration and isotopic chem- istry of specific molecules. These data can be analysed using either the moving Keeling or moving Miller-Tans methods (Vardag et al. 2016). In this presentation we show that continuous measurements taken within an emis- sion plume for at least an hour generate enough data to make better estimates of the population statistics that summarise the variability in the source category isotopic signature compared to a small set of grab bag samples, despite the analytic technique having lower precision than analysis of grab bag samples by isotope ratio mass spectrometry.We present examples of moving Miller-Tans analyses from urban gas leaks in Sydney, Australia, and analyses of the primary methane sources in the Surat Basin, Australia, including cattle feedlots, abandoned leaky exploration wells, and coal seam gas infrastructure. For each methane source we compare the moving Miller

Recent developments in laser-based cavity ring-down and off-axis spectroscopy have enabled the rapid measure- ment of both spatial and temporal atmospheric methane. Surveys of the mole fraction of methane ([CH4]) in the ground-level atmosphere have been undertaken in a number of cities including Warsaw, Nagoya, Los Angeles, Boston, Washington (D.C.), Florence and London. These mobile surveys were recorded during daylight hours.We present the advantages of undertaking methane source identification surveys between sunset and sun- rise when the boundary layer is low. This maximises the range of [CH4] and isotopic composition (d13C_CH4) values recorded, and reduces the uncertainty in Keeling plot analyses. This is particularly important in temperate, subtropical, tropical and desert environments where there is a steep heat gradient from the ground surface to the upper atmosphere, which results in rapid upwards convection during daylight hours. To support our argument, we present continuous diel [CH4] and d13C_CH4 measurements recorded in a typical urban laneway located in the Eastern Suburbs of Sydney, Australia. These data were collected in May and June 2016 during a calm weather period.We continuously measured the [CH4] and d13C_CH4 using a Picarro G2201-i. The raw data were smoothed using a wavelet analysis method, sampled on a one-minute interval, and analysed using the moving Keeling plot method. Both the [CH4] and d13C_CH4 signals display strong diel fluctuations. The lowest ([CH4] = 1.79 ppm) and highest ([CH4] = 3.07 ppm) readings were recorded during daylight and night-time hours, respectively. The diel d13C_CH4 signature reflects the interplay between urban activities, changing wind speed, shifting wind direction, and the fluctuating atmospheric boundary layer. Background air, extracted from the afternoon signal, has mean [CH4] and d13C_CH4 of 1.81 ± 0.01 ppm and -48.7 ± 0.4 respectively. Between sunset and sunrise, as the boundary layer lowers and the air fro

Airborne measurements of a methane (CH4) plume over the North Sea from August 2013 are analyzed. The plume was only observed downwind of circumnavigated gas fields, and three methods are used to determine its source. First, a mass balance calculation assuming a gas field source gives a CH4 emission rate between 2.5±0.8x104 and 4.6±1.5x104 kg h−1. This would be greater than the industry target of a 0.5% leak rate if it were emitting for more than half the time. Second, annual average UK CH4 emissions are combined with an atmospheric dispersion model to create pseudo-observations. Clean air from the North Atlantic passed over mainland UK, picking up anthropogenic emissions. To best explain the observed plume using pseudo-observations, an additional North Sea source from the gas rigs area is added. Third, the δ13C-CH4 from the plume is shown to be -53%0, which is lighter than fossil gas but heavier than the UK average emission. We conclude that either an additional small-area mainland source is needed, combined with temporal variability in emission or transport in small-scale meteorological features. Alternatively, a combination of additional sources that are at least 75% from the mainland (-58%0) and up to 25% from the North Sea gas rigs area (-32%0) would explain the measurements. Had the isotopic analysis not been performed, the likely conclusion would have been of a gas field source of CH4. This demonstrates the limitation of analysing mole fractions alone, as the simplest explanation is rejected based on analysis of isotopic data.

Bottom-up global methane emission estimates are important for guiding policy development and mitigation strategies. Such inventories enable rapid and consistent proportioning of emissions by industrial sectors and land use at various scales from city to country to global. There has been limited use of top-down measurements to guide refining emission inventories. Here we compare the EDGAR gridmap data version 4.2 with over 5000 km of daytime ground level mobile atmospheric methane surveys in eastern Australia. The landscapes and industries surveyed include: urban environments, dryland farming, intensive livestock farming (both beef and lamb), irrigation agriculture, open cut and underground coal mining, and coal seam gas production.Daytime mobile methane surveys over a 2-year period show that at the landscape scale there is a high level of repeatability for the mole fraction of methane measured in the ground level atmosphere. Such consistency in the mole fraction of methane indicates that these data can be used as a proxy for flux.A scatter plot of the EDGAR emission gridmap Log[ton substance / 0.1 degree x 0.1 degree / year] versus the median mole fraction of methane / 0.1 degree x 0.1 degree in the ground level atmosphere highlights that the extent of elevated methane emissions associated with coal mining in the Hunter coalfields, which covers an area of 56 km by 24 km, has been under-represented in the EDGAR input data.Our results also show that methane emissions from country towns (population < 100,000) are underesti- mated in the EDGAR inventory. This is possibly due to poor information on the extent of urban gas leaks.Given the uncertainties associated with the base land use and industry data for each country, we generalise the Australian observations to the global inventory with caution. The extensive comparison of top-down measurements versus the EDGAR version 4.2 methane gridmaps highlights the need for adjustments to the base resource data and/or the emissi

© Author(s) 2016. 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 ?13CCH4 signatures of methane emissions from specific coalfields. Integrated methane emissions from both underground and opencast coal mines in the UK, Australia and Poland were sampled 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 ĝfirst>'65ĝ€first>‰ has been assigned to bituminous coal exploited in open cast mines and of ĝfirst>'55ĝ€first>‰ in deep mines, whereas values of ĝfirst>'40 and ĝfirst>'30ĝ€first>‰ 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.

Modern cavity ringdown spectroscopy systems (CRDS) enable the continuous measurement of methane concentration. This allows for improved quantification of greenhouse gas emissions associated with various natural and human landscapes. We present a subset of over 4000 km of continuous methane surveying along the east coast of Australia, made using a Picarro G2301 CRDS, deployed in a utility vehicle with an air inlet above the roof at 2.2 mAGL. Measurements were made every 5 seconds to a precision of <0.5 ppb for CH4. These surveys were undertaken during dry daytime hours and all measurements were moisture corrected. We compare the concentration of methane in the near surface atmosphere adjacent to open-cut coal mines, unconventional gas developments (coal seam gas; CSG), and leaks detected in cities and country towns. In areas of dryland crops the median methane concentration was 1.78 ppm, while in the irrigation districts located on vertisol soils the concentration was as low as 1.76 ppm, which may indicate that these soils are a sink for methane. In the Hunter Valley, New South Wales, open-cut coal mining district we mapped a continuous 50 km interval where the concentration of methane exceeded 1.80 ppm. The median concentration in this interval was 2.02 ppm. Peak readings were beyond the range of the reliable measurement (in excess of 3.00 ppm). This extended plume is an amalgamation of plumes from 17 major pits 1 to 10 km in length. Adjacent to CSG developments in the Surat Basin, southeast Queensland, only small anomalies were detected near the well-heads. Throughout the vast majority of the gas fields the concentration of methane was below 1.80 ppm. The largest source of fugitive methane associated with CSG was off-gassing methane from the co-produced water holding ponds. At one location the down wind plume had a cross section of approximately 1 km where the concentration of methane was above 1.80 ppm. The median concentration within this section was 1.82 ppm, wi

There is considerable public concern that coal seam gas (CSG) production will affect groundwater quality and quantity in adjacent or overlying aquifers. To assess this risk there is a need to map pathways of hydraulic connectivity using geochemical and hydraulic measurements. We demonstrate that measurements of methane concentration and isotopic composition, dissolved organic carbon isotopes and tritium activity data delineate potential pathways of hydraulic connectivity between the Walloon Coal Measures (WCM - the target formation for CSG production) and the Condamine Alluvium, which is the primary freshwater aquifer in the Condamine Catchment, south-east Queensland, Australia.The Walloon Coal Measures is a 700 m thick, low-rank CSG resource that is overlain by sandstone formations, which form part of the Great Artesian Basin (GAB). The Condamine Alluvium fills a paleovalley carved through the above formations.At 19 locations, both groundwater and degassing air samples were collected from irrigation bores. Degassing air samples were collected using an SKC 222-2301 air pump, which pumped the gas into 3 L Tedlar bags. The groundwater was analysed for tritium and dissolved organic carbon isotopes. A mobile methane survey was undertaken to collect continuous air samples around areas of agricultural and unconventional gas production. We use isotope mixing plots to identify the isotopic source signature of methane in the air samples from the off gassing irrigation bores and ambient air samples adjacent to CSG water holding ponds. Samples cluster along clear trend lines within the mixing plot and indicate potential local natural hydraulic connectivity between the target WCM and the overlying Condamine Alluvium.

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 campaign. 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 campaign. 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.