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Atmospheric methane (CH4) is a potent greenhouse gas, and its mole fraction has more than doubled since the preindustrial era1. Fossil fuel extraction and use are among the largest anthropogenic sources of CH4 emissions, but the precise magnitude of these contributions is a subject of debate2,3. Carbon-14 in CH4 (14CH4) can be used to distinguish between fossil (14C-free) CH4 emissions and contemporaneous biogenic sources; however, poorly constrained direct 14CH4 emissions from nuclear reactors have complicated this approach since the middle of the 20th century4,5. Moreover, the partitioning of total fossil CH4 emissions (presently 172 to 195 teragrams CH4 per year)2,3 between anthropogenic and natural geological sources (such as seeps and mud volcanoes) is under debate; emission inventories suggest that the latter account for about 40 to 60 teragrams CH4 per year6,7. Geological emissions were less than 15.4 teragrams CH4 per year at the end of the Pleistocene, about 11,600 years ago8, but that period is an imperfect analogue for present-day emissions owing to the large terrestrial ice sheet cover, lower sea level and extensive permafrost. Here we use preindustrial-era ice core 14CH4 measurements to show that natural geological CH4 emissions to the atmosphere were about 1.6 teragrams CH4 per year, with a maximum of 5.4 teragrams CH4 per year (95 per cent confidence limit)-an order of magnitude lower than the currently used estimates. This result indicates that anthropogenic fossil CH4 emissions are underestimated by about 38 to 58 teragrams CH4 per year, or about 25 to 40 per cent of recent estimates. Our record highlights the human impact on the atmosphere and climate, provides a firm target for inventories of the global CH4 budget, and will help to inform strategies for targeted emission reductions9,10.

Abstract. We reconstruct atmospheric abundances of the potentgreenhouse gas c-C4F8 (perfluorocyclobutane, perfluorocarbonPFC-318) from measurements of in situ, archived, firn, and aircraft airsamples with precisions of ∼1 %–2 % reported on the SIO-14gravimetric calibration scale. Combined with inverse methods, we found near-zero atmospheric abundances from the early 1900s to the early 1960s, afterwhich they rose sharply, reaching 1.66 ppt (parts per trillion dry-air molefraction) in 2017. Global c-C4F8 emissions rose from near zero inthe 1960s to 1.2±0.1 (1σ) Gg yr−1 in the late 1970s tolate 1980s, then declined to 0.77±0.03 Gg yr−1 in the mid-1990sto early 2000s, followed by a rise since the early 2000s to 2.20±0.05 Gg yr−1 in 2017. These emissions are significantly larger thaninventory-based emission estimates. Estimated emissions from eastern Asiarose from 0.36 Gg yr−1 in 2010 to 0.73 Gg yr−1 in 2016 and 2017,31 % of global emissions, mostly from eastern China. We estimateemissions of 0.14 Gg yr−1 from northern and central India in 2016 andfind evidence for significant emissions from Russia. In contrast, recentemissions from northwestern Europe and Australia are estimated to be small(≤1 % each). We suggest that emissions from China, India, and Russiaare likely related to production of polytetrafluoroethylene (PTFE,“Teflon”) and other fluoropolymers and fluorochemicals that are based onthe pyrolysis of hydrochlorofluorocarbon HCFC-22 (CHClF2) in whichc-C4F8 is a known by-product. The semiconductor sector, wherec-C4F8 is used, is estimated to be a small source, at least inSouth Korea, Japan, Taiwan, and Europe. Without an obvious correlation withpopulation density, incineration of waste-containing fluoropolymers isprobably a minor source, and we find no evidence of emissions fromelectrolytic production of aluminum in Australia. While many possibleemissive uses of c-C4F8 are known and though we cannotcategorically exclude unknown sources, the start of significant emissionsmay well be related to the advent of commercial PTFE production in 1947.Process controls or abatement to reduce the c-C4F8 by-product wereprobably not in place in the early decades, explaining the increase inemissions in the 1960s and 1970s. With the advent of by-product reportingrequirements to the United Nations Framework Convention on Climate Change(UNFCCC) in the 1990s, concern about climate change and product stewardship,abatement, and perhaps the collection of c-C4F8 by-product for usein the semiconductor industry where it can be easily abated, it isconceivable that emissions in developed countries were stabilized and thenreduced, explaining the observed emission reduction in the 1980s and 1990s.Concurrently, production of PTFE in China began to increase rapidly. Withoutemission reduction requirements, it is plausible that global emissions todayare dominated by China and other developing countries. We predict thatc-C4F8 emissions will continue to rise and that c-C4F8will become the second most important emitted PFC in terms ofCO2-equivalent emissions within a year or two. The 2017 radiativeforcing of c-C4F8 (0.52 mW m−2) is small but emissions ofc-C4F8 and other PFCs, due to their very long atmosphericlifetimes, essentially permanently alter Earth's radiative budget and shouldbe reduced. Significant emissions inferred outside of the investigatedregions clearly show that observational capabilities and reportingrequirements need to be improved to understand global and country-scaleemissions of PFCs and other synthetic greenhouse gases and ozone-depletingsubstances.

Galactic cosmic rays (GCRs) interact with matter in the atmosphere and at the surface of the Earth to produce a range of cosmogenic nuclides. Measurements of cosmogenic nuclides produced in surface rocks have been used to study past land ice extent as well as to estimate erosion rates. Because the GCR flux reaching the Earth is modulated by magnetic fields (solar and Earth's), records of cosmogenic nuclides produced in the atmosphere have also been used for studies of past solar activity. Studies utilizing cosmogenic nuclides assume that the GCR flux is constant in time, but this assumption may be uncertain by 30 % or more. Here we propose that measurements of 14 C of carbon monoxide (14 CO) in ice cores at low-accumulation sites can be used as a proxy for variations in GCR flux on timescales of several thousand years. At low-accumulation ice core sites, 14 CO in ice below the firn zone originates almost entirely from in situ cosmogenic production by deep-penetrating secondary cosmic ray muons. The flux of such muons is almost insensitive to solar and geomagnetic variations and depends only on the primary GCR flux intensity. We use an empirically constrained model of in situ cosmogenic 14 CO production in ice in combination with a statistical analysis to explore the sensitivity of ice core 14 CO measurements at Dome C, Antarctica, to variations in the GCR flux over the past ≈ 7000 years. We find that Dome C 14 CO measurements would be able to detect a linear change of 6 % over 7 ka, a step increase of 6 % at 3.5 ka or a transient 100-year spike of 190 % at 3.5 ka at the 3 σ significance level. The ice core 14 CO proxy therefore appears promising for the purpose of providing a high-precision test of the assumption of GCR flux constancy over the Holocene. [ABSTRACT FROM AUTHOR]

Atmospheric methane (CH.sub.4) is a potent greenhouse gas, and its mole fraction has more than doubled since the preindustrial era.sup.1. Fossil fuel extraction and use are among the largest anthropogenic sources of CH.sub.4 emissions, but the precise magnitude of these contributions is a subject of debate.sup.2,3. Carbon-14 in CH.sub.4 (.sup.14CH.sub.4) can be used to distinguish between fossil (.sup.14C-free) CH.sub.4 emissions and contemporaneous biogenic sources; however, poorly constrained direct .sup.14CH.sub.4 emissions from nuclear reactors have complicated this approach since the middle of the 20th century.sup.4,5. Moreover, the partitioning of total fossil CH.sub.4 emissions (presently 172 to 195 teragrams CH.sub.4 per year).sup.2,3 between anthropogenic and natural geological sources (such as seeps and mud volcanoes) is under debate; emission inventories suggest that the latter account for about 40 to 60 teragrams CH.sub.4 per year.sup.6,7. Geological emissions were less than 15.4 teragrams CH.sub.4 per year at the end of the Pleistocene, about 11,600 years ago.sup.8, but that period is an imperfect analogue for present-day emissions owing to the large terrestrial ice sheet cover, lower sea level and extensive permafrost. Here we use preindustrial-era ice core .sup.14CH.sub.4 measurements to show that natural geological CH.sub.4 emissions to the atmosphere were about 1.6 teragrams CH.sub.4 per year, with a maximum of 5.4 teragrams CH.sub.4 per year (95 per cent confidence limit)--an order of magnitude lower than the currently used estimates. This result indicates that anthropogenic fossil CH.sub.4 emissions are underestimated by about 38 to 58 teragrams CH.sub.4 per year, or about 25 to 40 per cent of recent estimates. Our record highlights the human impact on the atmosphere and climate, provides a firm target for inventories of the global CH.sub.4 budget, and will help to inform strategies for targeted emission reductions.sup.9,10. Isotopic evidence from ice cores indicates that preindustrial-era geological methane emissions were lower than previously thought, suggesting that present-day emissions of methane from fossil fuels are underestimated., Author(s): Benjamin Hmiel [sup.1] , V. V. Petrenko [sup.1] , M. N. Dyonisius [sup.1] , C. Buizert [sup.2] , A. M. Smith [sup.3] , P. F. Place [sup.1] , C. [...]

Measurements of carbon-14-containing carbon monoxide (14 CO) in glacial ice are useful for studies of the past oxidative capacity of the atmosphere as well as for reconstructing the past cosmic ray flux. The 14 CO abundance in glacial ice represents the combination of trapped atmospheric 14 CO and in situ cosmogenic 14 CO. The systematics of in situ cosmogenic 14 CO production and retention in ice are not fully quantified, posing an obstacle to interpretation of ice core 14 CO measurements. Here we provide the first comprehensive characterization of 14 CO at an ice accumulation site (Summit, Greenland), including measurements in the ice grains of the firn matrix, firn air and bubbly ice below the firn zone. The results are interpreted with the aid of a firn gas transport model into which we implemented in situ cosmogenic 14 C. We find that almost all (≈ 99.5 %) of in situ 14 CO that is produced in the ice grains in firn is very rapidly (in <1 year) lost to the open porosity and from there mostly vented to the atmosphere. The timescale of this rapid loss is consistent with what is expected from gas diffusion through ice. The small fraction of in situ 14 CO that initially stays in the ice grains continues to slowly leak out to the open porosity at a rate of ≈ 0.6 % yr -1. Below the firn zone we observe an increase in 14 CO content with depth that is due to in situ 14 CO production by deep-penetrating muons, confirming recent estimates of 14 CO production rates in ice via the muon mechanisms and allowing for narrowing constraints on these production rates. [ABSTRACT FROM AUTHOR]

Galactic cosmic rays (GCRs) interact with matter in the atmosphere and at the surface of the Earth to produce a range of cosmogenic nuclides. Measurements of cosmogenic nuclides produced in surface rocks have been used to study past land ice extent as well as to estimate erosion rates. Because the GCR flux reaching the Earth is modulated by magnetic fields (solar and Earth's), records of cosmogenic nuclides produced in the atmosphere have also been used for studies of past solar activity. Studies utilizing cosmogenic nuclides assume that the GCR flux is constant in time, but this assumption may be uncertain by 30% or more. Here we propose that measurements of 14C of carbon monoxide (14CO) in ice cores at low-accumulation sites can be used as a proxy for variations in GCR flux on timescales of several thousand years. At low-accumulation ice core sites, 14CO in ice below the firn zone originates almost entirely from in situ cosmogenic production by deep-penetrating secondary cosmic ray muons. The flux of such muons is insensitive to solar and geomagnetic variations, and depends only on the primary GCR flux intensity. We use an empirically-constrained model of in situ cosmogenic 14CO production in ice in combination with a statistical analysis to explore the sensitivity of ice core 14CO measurements at Dome C, Antarctica to variations in the GCR flux over the past ≈7000 years. We find that Dome C 14CO measurements would be able to detect a linear change of 4%, a step increase of 4% or a transient 100-year spike of 250% at the 3 σ significance level. The ice core 14CO proxy therefore appears promising for the purpose of providing a high-precision test of the assumption of GCR flux constancy over the Holocene. [ABSTRACT FROM AUTHOR]

Measurements of carbon-14-containing carbon monoxide (14CO) in glacial ice are useful for studies of the past oxidative capacity of the atmosphere as well as for reconstructing the past cosmic ray flux. 14CO abundance in glacial ice represents the combination of trapped atmospheric 14CO and in situ cosmogenic 14CO. The systematics of in situ cosmogenic 14CO production and retention in ice are not fully quantified, posing an obstacle to interpretation of ice core 14CO measurements. Here we provide the first comprehensive characterization of 14CO at an ice accumulation site (Summit, Greenland), including measurements in the ice grains of the firn matrix, firn air and bubbly ice below the firn zone. The results are interpreted with the aid of a firn gas transport model into which we implemented in situ cosmogenic 14C. We find that almost all (≈99.5%) of in situ 14CO that is produced in the ice grains in firn is very rapidly (in <1 year) lost to the open porosity and from there mostly vented to the atmosphere. The time scale of this rapid loss is consistent with what is expected from gas diffusion through ice. The small fraction of in situ 14CO that initially stays in the ice grains continues to slowly leak out to the open porosity at a rate of ≈0.6% per year. Below the firn zone we observe an increase in 14CO content with depth that is due to in situ 14CO production by deep-penetrating muons, confirming recent estimates of production rates in ice via the muon mechanisms and allowing for narrowing constraints on these production rates. [ABSTRACT FROM AUTHOR]

We quantify weekly methane emissions at 0.25 ∘ × 0.3125 ∘ (≈25 × 25 km 2) resolution from the Permian Basin, the largest oil production basin in the US, by inverse analysis of satellite observations from the TROPOspheric Monitoring Instrument (TROPOMI) from May 2018 to October 2020. The mean oil and gas emission from the region (± standard deviation of weekly estimates) was 3.7 ± 0.9 Tg a -1 , higher than previous TROPOMI inversion estimates that may have used biased prior emissions or background assumptions. We find strong week-to-week variability in emissions superimposed on longer-term trends, and these are consistent with independent inferences of temporal emission variability from tower, aircraft, and multispectral satellite data. New well development and natural gas spot price were significant drivers of variability in emissions over our study period but the concurrent 50 % increase in oil and gas production was not. The methane intensity (methane emitted per unit of methane gas produced) averaged 4.6 % ± 1.3 % and steadily decreased from 5 %–6 % in 2018 to 3 %–4 % in 2020. While the decreasing trend suggests improvement in operator practices during the study period, methane emissions from the Permian Basin remained high, with methane intensity an order of magnitude above the industry target of <0.2 %. Our success in using TROPOMI satellite observations for weekly estimates of emissions from a major oil production basin shows promise for application to near-real-time monitoring in support of climate change mitigation efforts. [ABSTRACT FROM AUTHOR]

The United States is the world's largest oil/gas methane emitter according to current national reports. Reducing these emissions is a top priority in the US government's climate action plan. Here, we use a 2010 to 2019 high-resolution inversion of surface and satellite observations of atmospheric methane to quantify emission trends for individual oil/gas production regions in North America and relate them to production and infrastructure. We estimate a mean US oil/gas methane emission of 14.8 (12.4 to 16.5) Tg a-1 for 2010 to 2019, 70% higher than reported by the US Environmental Protection Agency. While emissions in Canada and Mexico decreased over the period, US emissions increased from 2010 to 2014, decreased until 2017, and rose again afterward. Increases were driven by the largest production regions (Permian, Anadarko, Marcellus), while emissions in the smaller production regions generally decreased. Much of the year-to-year emission variability can be explained by oil/gas production rates, active well counts, and new wells drilled, with the 2014 to 2017 decrease driven by reduction in new wells and the 2017 to 2019 surge driven by upswing of production. We find a steady decrease in the oil/gas methane intensity (emission per unit methane gas production) for almost all major US production regions. The mean US methane intensity decreased from 3.7% in 2010 to 2.5% in 2019. If the methane intensity for the oil/gas supply chain continues to decrease at this pace, we may expect a 32% decrease in US oil/gas emissions by 2030 despite projected increases in production. [ABSTRACT FROM AUTHOR]

According to the United States Environmental Protection Agency (US EPA), emissions from oil and gas infrastructure contribute 30 % of all anthropogenic methane (CH4) emissions in the US. Studies in the last decade have shown emissions from this sector to be substantially larger than bottom-up assessments, including the EPA inventory, highlighting both an increased importance of methane emissions from the oil and gas sector towards their overall climatological impact, and the need for independent monitoring of these emissions. In this study we present continuous monitoring of regional methane emissions from two oil and gas basins using tower-based observing networks. Continuous methane measurements were taken at 4 tower sites in the northeastern Marcellus basin from May 2015 through December 2016, and 5 tower sites in the Delaware basin in the western Permian from March 2020 through April 2022. These measurements, an atmospheric transport model, and prior emission fields, are combined using an atmospheric inversion to estimate monthly methane emissions in the two regions. This study finds the mean overall emission rate from the Delaware basin during the measurement period to be 146-210 Mg CH4 h-1 (energy-normalized loss rate of 1.1-1.5 %, gas-normalized rate of 2.5-3.5 %). Strong temporal variability in the emissions was present, with the lowest emission rates occurring during the onset of the COVID-19 pandemic. In the Marcellus, this study finds the overall mean emission rate to be 19-28 Mg CH4 h-1 (gas-normalized loss rate of 0.30-0.45 %), with relative consistency in the emission rate over time. These totals align with aircraft top-down estimates from the same time periods. In both basins, the tower network was able to constrain monthly flux estimates within ± 20 % uncertainty in the Delaware and ± 24 % uncertainty in the Marcellus. The results from this study demonstrate the ability to monitor emissions continuously and detect changes in the emissions field, even in a basin with relatively small emissions and complex background conditions. [ABSTRACT FROM AUTHOR]

We quantify weekly methane emissions at 0.25°×0.3125° (≈25×25 km²) resolution from the Permian Basin, the largest oil production basin in the United States, by inverse analysis of satellite observations from the TROPOspheric Monitoring Instrument (TROPOMI) from May 2018 to October 2020. The mean oil and gas emission from the region (± standard deviation of weekly estimates) was 3.7 ± 0.9 Tg a-1, higher than previous TROPOMI inversion estimates that may have used too-low prior emissions or biased background assumptions. We find strong week-to-week variability in emissions superimposed on longer-term trends, and these are consistent with independent inferences of temporal emission variability from tower, aircraft, and multispectral satellite data. New well development and local natural gas spot price were significant drivers of variability in emissions over our study period, but the concurrent 50 % increase in oil and gas production was not. The methane intensity (methane emitted per unit of methane gas produced) averaged 4.6 % ± 1.3 % and steadily decreased over the period from 5–6 % in 2018 to 3–4 % in 2020. While the decreasing trend suggests improvement in operator practices during the study period, methane emissions from the Permian Basin remained high, with methane intensity an order of magnitude above recent industry targets of <0.2 %. Our success in using TROPOMI satellite observations for weekly estimates of emissions from a major oil production basin shows promise for application to near-real-time monitoring in support of climate change mitigation efforts. [ABSTRACT FROM AUTHOR]

Methane emissions associated with the production, transport, and use of oil and natural gas increase the climatic impacts of energy use; however, little is known about how emissions vary temporally and with commodity prices. We present airborne and ground-based data, supported by satellite observations, to measure weekly to monthly changes in total methane emissions in the United States' Permian Basin during a period of volatile oil prices associated with the COVID-19 pandemic. As oil prices declined from ~$ 60 to $ 20 per barrel, emissions changed concurrently from 3.4 % to 1.5 % of gas production; as prices partially recovered, emissions increased back to near initial values. Concurrently, total oil and natural gas production only declined by a maximum of ~10 % from the peak values seen in the months prior to the crash. Activity data indicate that a rapid decline in well development and subsequent effects on associated gas flaring and midstream infrastructure throughput are the likely drivers of temporary emission reductions. Our results, along with past satellite observations, suggest that under more typical price conditions, the Permian Basin is in a state of overcapacity in which rapidly growing natural gas production exceeds midstream capacity and leads to high methane emissions. [ABSTRACT FROM AUTHOR]

Concentrations of atmospheric methane (CH4), a potent greenhouse gas, have more thandoubled since preindustrial times yet its contemporary budget is incompletely understood,with substantial discrepancies between global emission inventories and atmosphericobservations (Kirschke et al., 2013; Saunois et al., 2016). Radiomethane (14CH4) candistinguish between fossil emissions from geologic reservoirs (radiocarbon free) andcontemporaneous biogenic sources, although poorly constrained direct 14CH4 emissionsfrom nuclear reactors complicate this interpretation in the modern era (Lassey et al.,2007; Zazzeri et al 2018). It has been debated how fossil emissions (172-195 TgCH4/yr, (Saunois et al., 2016; Schwietzke et al., 2016)) are partitioned betweenanthropogenic sources (such as fossil fuel extraction and consumption) and naturalsources (such as geologic seeps); emission inventories suggest the latter accountsfor ∼50-60 Tg CH4/yr (Etiope, 2015; Etiope et al., 2008). Geologic emissionswere recently shown to be much smaller at the end of the Pleistocene ∼11,600years ago (Petrenko et al. 2017); However, this period is an imperfect analog for thepresent day due to the much larger terrestrial ice sheet cover, lowered sea level,and more extensive permafrost. We use preindustrial ice core measurements of14CH4 to show that natural fossil CH4 emissions to the atmosphere are ∼1.7 TgCH4/yr, with a maximum of 6.1 Tg CH4/yr (95% confidence limit), an order ofmagnitude smaller than estimates from global inventories. This result suggeststhat contemporary anthropogenic fossil emissions are likely underestimated by acorresponding amount (∼48-58 Tg CH4/yr, or ∼25-33% of current estimates). [ABSTRACT FROM AUTHOR]

The title compounds are synthesized from the elements using molten Ga as a flux (alumina crucible, 1473 K, 24 h) and characterized by single crystal and powder XRD, and magnetic susceptibility measurements. [ABSTRACT FROM AUTHOR]

Single crystals of the title compounds are prepared from the elements using excess Bi as a flux (alumina crucible in a fused silica tube, 1273 K, 20 h). [ABSTRACT FROM AUTHOR]