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Cosmic rays entering the Earth's atmosphere produce showers of secondary particles such as protons, neutrons, and muons. The interaction of these particles with oxygen-16 (O-16) in minerals such as ice and quartz can produce carbon-14 (C-14). In glacial ice, C-14 is also incorporated through trapping of C-14-containing atmospheric gases ((CO2)-C-14,(CO)-C- 14, and (CH4)-C-14). Understanding the production rates of in situ cosmogenic C-14 is important to deconvolve the in situ cosmogenic and atmospheric( 14)C signals in ice, both of which contain valuable paleoenvironmental information. Unfortunately, the in situ C-14 production rates by muons (which are the dominant production mechanism at depths of > 6 m solid ice equivalent) are uncertain. In this study, we use measurements of in situ C-14 in ancient ice (> 50 ka) from the Taylor Glacier, an ablation site in Antarctica, in combination with a 2D ice flow model to better constrain the compound-specific rates of C-14 production by muons and the partitioning of in situ( 14)C between CO2, CO, and CH4. Our measurements show that 33.7 % (+/- 11.4%; 95 % confidence interval) of the produced cosmogenic C-14 forms (CO)-C-14 and 66.1 % (+/- 11.5%; 95 % confidence interval) of the produced cosmogenic C-14 forms (CO2)-C-14. (CH4)-C-14 represents a very small fraction (< 0.3%) of the total. Assuming that the majority of in situ muogenic 14C in ice forms (CO2)-C-14, (CO)-C-14, and (CH4)-C-14, we also calculated muogenic( 14)C production rates that are lower by factors of 5.7 (3.6-13.9; 95 % confidence interval) and 3.7 (2.0-11.9; 95 % confidence interval) for negative muon capture and fast muon interactions, respectively, when compared to values determined in quartz from laboratory studies (Heisinger et al., 2002a, b) and in a natural setting (Lupker et al., 2015). This apparent discrepancy in muogenic C-14 production rates in ice and quartz currently lacks a good explanation and requires further investigation.

Cosmic rays entering the Earth's atmosphere produce showers of secondary particles such as protons, neutrons, and muons. The interaction of these particles with oxygen-16 (O-16) in minerals such as ice and quartz can produce carbon-14 (C-14). In glacial ice, C-14 is also incorporated through trapping of C-14-containing atmospheric gases ((CO2)-C-14,(CO)-C- 14, and (CH4)-C-14). Understanding the production rates of in situ cosmogenic C-14 is important to deconvolve the in situ cosmogenic and atmospheric( 14)C signals in ice, both of which contain valuable paleoenvironmental information. Unfortunately, the in situ C-14 production rates by muons (which are the dominant production mechanism at depths of > 6 m solid ice equivalent) are uncertain. In this study, we use measurements of in situ C-14 in ancient ice (> 50 ka) from the Taylor Glacier, an ablation site in Antarctica, in combination with a 2D ice flow model to better constrain the compound-specific rates of C-14 production by muons and the partitioning of in situ( 14)C between CO2, CO, and CH4. Our measurements show that 33.7 % (+/- 11.4%; 95 % confidence interval) of the produced cosmogenic C-14 forms (CO)-C-14 and 66.1 % (+/- 11.5%; 95 % confidence interval) of the produced cosmogenic C-14 forms (CO2)-C-14. (CH4)-C-14 represents a very small fraction (< 0.3%) of the total. Assuming that the majority of in situ muogenic 14C in ice forms (CO2)-C-14, (CO)-C-14, and (CH4)-C-14, we also calculated muogenic( 14)C production rates that are lower by factors of 5.7 (3.6-13.9; 95 % confidence interval) and 3.7 (2.0-11.9; 95 % confidence interval) for negative muon capture and fast muon interactions, respectively, when compared to values determined in quartz from laboratory studies (Heisinger et al., 2002a, b) and in a natural setting (Lupker et al., 2015). This apparent discrepancy in muogenic C-14 production rates in ice and quartz currently lacks a good explanation and requires further investigation.

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.

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.

[EN] Industrial emissions play a major role in the global methane budget. The Permian basin is thought to be responsible for almost half of the methane emissions from all U.S. oil- and gas-producing regions, but little is known about individual contributors, a prerequisite for mitigation. We use a new class of satellite measurements acquired during several days in 2019 and 2020 to perform the first regional-scale and high-resolution survey of methane sources in the Permian. We find an unexpectedly large number of extreme point sources (37 plumes with emission rates >500 kg hour(-1)), which account for a range between 31 and 53% of the estimated emissions in the sampled area. Our analysis reveals that new facilities are major emitters in the area, often due to inefficient flaring operations (20% of detections). These results put current practices into question and are relevant to guide emission reduction efforts.

We reconstruct atmospheric abundances of the potent greenhouse gas span classCombining double low line inline-formula span classCombining double low line inline-formula perfluorocyclobutane, perfluorocarbon PFC-318) from measurements of in situ, archived, firn, and aircraft air samples with precisions of span classCombining double low line inline-formula reported on the SIO-14 gravimetric calibration scale. Combined with inverse methods, we found near-zero atmospheric abundances from the early 1900s to the early 1960s, after which they rose sharply, reaching 1.66ppt (parts per trillion dry-air mole fraction) in 2017. Global span classCombining double low line inline-formula span classCombining double low line inline-formula emissions rose from near zero in the 1960s to span classCombining double low line inline-formula (1span classCombining double low line inline-formula gyrspan classCombining double low line inline-formula in the late 1970s to late 1980s, then declined to span classCombining double low line inline-formula classCombining double low line inline-formula in the mid-1990s to early 2000s, followed by a rise since the early 2000s to span classCombining double low line inline-formula 2.20±0.05 Ggyrspan classCombining double low line inline-formula in 2017. These emissions are significantly larger than inventory-based emission estimates. Estimated emissions from eastern Asia rose from 0.36Ggyrspan classCombining double low line inline-formula in 2010 to 0.73Ggyrspan classCombining double low line inline-formula in 2016 and 2017, 31% of global emissions, mostly from eastern China. We estimate emissions of 0.14Ggyrspan classCombining double low line inline-formula from northern and central India in 2016 and find evidence for significant emissions from Russia. In contrast, recent emissions from northwestern Europe and Australia are estimated to be small (span classCombining double low line inline-formula % each). We suggest that emissions from China, India, an, United States. National Aeronautics and Space Administration (Grant NNX07AE89G), United States. National Aeronautics and Space Administration (Grant NNX07AF09G), United States. National Aeronautics and Space Administration (Grant NNX07AE87G), Great Britain. Department for Business, Energy & Industrial Strategy (Grant 1028/06/2015), United States. National Oceanic and Atmospheric Administration (Grant RA-133-R15-CN-0008), National Natural Science Foundation of China (Grant 41575114), National Science Foundation (U.S.) (Grant ARC-1203779), National Science Foundation (U.S.) (Grant ARC-1204084), Natural Environment Research Council (Great Britain) (Grant NE/I027282/1)

Carbon-14 ($^{14}$C) is produced in the atmosphere when neutrons from cosmic-ray air showers are captured by $^{14}$N nuclei. Atmospheric $^{14}$C becomes trapped in air bubbles in polar ice as compacted snow (firn) transforms into ice. $^{14}$C is also produced in situ in ice grains by penetrating cosmic-ray neutrons and muons. Recent ice core measurements indicate that in the $^{14}$CO phase, the $^{14}$C is dominated by the in situ cosmogenic component at most ice coring sites. Thus, it should be possible to use ice-bound $^{14}$CO to reconstruct the historical flux of cosmic rays at Earth, without the transport and deposition uncertainties associated with $^{10}$Be or the carbon cycle uncertainties affecting atmospheric $^{14}$CO$_2$. The measurements will be sensitive to the cosmic-ray flux above the energy range most affected by solar modulation. We present estimates of the expected sensitivity of $^{14}$CO in ice cores to the historical flux of Galactic cosmic rays, based on recent studies of $^{14}$CO in polar ice., Comment: Presented at the International Cosmic Ray Conference (ICRC2019) in Madison, WI, USA, July 2019. 8 pages, 2 figures

We reconstruct atmospheric abundances of the potent greenhouse gas c-C4F8 (perfluorocyclobutane, perfluorocarbon PFC-318) from measurements of in situ, archived, firn, and aircraft air samples with precisions of ~ 1–2 % reported on the SIO-14 gravimetric calibration scale. Combined with inverse methods, we found near zero atmospheric abundances from the early 1900s to the early 1960s, after which they rose sharply, reaching 1.66 ppt (parts per trillion dry-air mole fraction) in 2017. Global c-C4F8 emissions rose from near zero in the 1960s to ~ 1.2 Gg yr−1 in the late 1970s to late 1980s, then declined to ~ 0.8 Gg yr−1 in the mid-1990s to early 2000s, followed by a rise since the early 2000s to ~ 2.2 Gg yr−1 in 2017. These emissions are significantly larger than inventory based emission estimates. Estimated emissions from eastern Asia rose 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 estimate emissions of 0.14 Gg yr−1 from Northern and Central India in 2016 and find evidence for significant emissions from Russia. In contrast, recent emissions from North Western Europe and Australia are estimated to be small (≤ 1 % each). We conclude that emissions from China, India and Russia are likely related to production of polytetrafluoroethylene (PTFE, “Teflon”) and other fluoropolymers that are based on the pyrolysis of hydrochlorofluorocarbon HCFC-22 (CHClF2) in which c-C4F8 is a known by-product. The semiconductor sector, where c-C4F8 is used, is estimated to be a small source. Without an obvious correlation with population density, incineration of waste containing fluoropolymers is probably a minor source, and we find no evidence of emissions from electrolytic production of aluminum in Australia. While many possible emissive uses of c-C4F8 are known, the start of significant emissions may well be related to the advent of commercial PTFE production in 1947. Process controls or abatement to redu

We reconstruct atmospheric abundances of the potent greenhouse gas c-C4F8 (perfluorocyclobutane, perfluorocarbon PFC-318) from measurements of in situ, archived, firn, and aircraft air samples with precisions of ~ 1–2 % reported on the SIO-14 gravimetric calibration scale. Combined with inverse methods, we found near zero atmospheric abundances from the early 1900s to the early 1960s, after which they rose sharply, reaching 1.66 ppt (parts per trillion dry-air mole fraction) in 2017. Global c-C4F8 emissions rose from near zero in the 1960s to ~ 1.2 Gg yr−1 in the late 1970s to late 1980s, then declined to ~ 0.8 Gg yr−1 in the mid-1990s to early 2000s, followed by a rise since the early 2000s to ~ 2.2 Gg yr−1 in 2017. These emissions are significantly larger than inventory based emission estimates. Estimated emissions from eastern Asia rose 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 estimate emissions of 0.14 Gg yr−1 from Northern and Central India in 2016 and find evidence for significant emissions from Russia. In contrast, recent emissions from North Western Europe and Australia are estimated to be small (≤ 1 % each). We conclude that emissions from China, India and Russia are likely related to production of polytetrafluoroethylene (PTFE, “Teflon”) and other fluoropolymers that are based on the pyrolysis of hydrochlorofluorocarbon HCFC-22 (CHClF2) in which c-C4F8 is a known by-product. The semiconductor sector, where c-C4F8 is used, is estimated to be a small source. Without an obvious correlation with population density, incineration of waste containing fluoropolymers is probably a minor source, and we find no evidence of emissions from electrolytic production of aluminum in Australia. While many possible emissive uses of c-C4F8 are known, the start of significant emissions may well be related to the advent of commercial PTFE production in 1947. Process controls or abatement to redu

Carbon-14 ($^{14}$C) is produced in the atmosphere when neutrons from cosmic-ray air showers are captured by $^{14}$N nuclei. Atmospheric $^{14}$C becomes trapped in air bubbles in polar ice as compacted snow (firn) transforms into ice. $^{14}$C is also produced in situ in ice grains by penetrating cosmic-ray neutrons and muons. Recent ice core measurements indicate that in the $^{14}$CO phase, the $^{14}$C is dominated by the in situ cosmogenic component at most ice coring sites. Thus, it should be possible to use ice-bound $^{14}$CO to reconstruct the historical flux of cosmic rays at Earth, without the transport and deposition uncertainties associated with $^{10}$Be or the carbon cycle uncertainties affecting atmospheric $^{14}$CO$_2$. The measurements will be sensitive to the cosmic-ray flux above the energy range most affected by solar modulation. We present estimates of the expected sensitivity of $^{14}$CO in ice cores to the historical flux of Galactic cosmic rays, based on recent studies of $^{14}$CO in polar ice., Comment: Presented at the International Cosmic Ray Conference (ICRC2019) in Madison, WI, USA, July 2019. 8 pages, 2 figures

Thesis (Ph. D.)--University of Rochester. Department of Earth and Environmental Sciences, 2020., This body of work expands the understanding of in situ cosmogenic 14C production and retention in the upper layer of accumulating ice sheets and presents new measurements of 14CH4 that improve our understanding of the fossil component of the CH4 budget. Samples were collected at Summit, Greenland from the firn air open porosity, the firn matrix and from ice below the depth of bubble closure. Large volume (~100L STP) air samples requiring ~1000kg ice/sample were collected for measurements of 14CH4 and 14CO via on site melt-extraction. Air for 14CO2 analysis was extracted via sublimation of ~1 kg ice samples using a new technique developed as part of this thesis. A model of firn gas transport and in situ cosmogenic 14C production was used to interpret the 14CO results, finding that only ~0.5% of in situ cosmogenic 14C produced in the firn is retained by the accumulating ice crystal lattice. Further, production rates of 14C in ice from deeply-penetrating muons are found to be overestimated by a factor of 3-4. The in situ cosmogenic 14CO2 component in accumulating ice is demonstrated be smaller in magnitude than the combined uncertainty from measurement and model characterization of paleoatmospheric 14CO2 bubble trapping. This study also used the ice core and firn air measurements in combination with an inverse model to reconstruct the atmospheric history of 14CH4 back to ~1750 CE. The samples collected show that natural fossil CH4 emissions during the preindustrial were ~1.6 Tg CH4/yr, with a maximum of 5.4 Tg CH4/yr (95% confidence limit), an order of magnitude smaller than indicated by bottom-up inventories. Using this constraint to reassess the contemporary CH4 budget with an atmospheric box model of 13CH4 shows that anthropogenic CH4 emissions from the fossil fuel industry are currently underestimated by ~25-40%. This result provides additional clarity with respect to the global CH4 budget and will help to inform strategies for targeted emission reductions aiming t