Using ice core measurements from Taylor Glacier, Antarctica, to calibrate in situ cosmogenic 14 C production rates by muons

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 (16O) in minerals such as ice and quartz can produce carbon-14 (14C). In glacial ice, 14C is also incorporated through trapping of 14C-containing atmospheric gases (14CO2, 14CO, and 14CH4). Understanding the production rates of in situ cosmogenic 14C is important to deconvolve the in situ cosmogenic and atmospheric 14C signals in ice, both of which contain valuable paleoenvironmental information. Unfortunately, the in situ 14C production rates by muons (which are the dominant production mechanism at depths of > 6m solid ice equivalent) are uncertain. In this study, we use measurements of in situ 14C 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 14C production by muons and the partitioning of in situ 14C between CO2, CO, and CH4. Our measurements show that 33.7% (11.4%; 95% confidence interval) of the produced cosmogenic 14C forms 14CO and 66.1% (11.5%; 95% confidence interval) of the produced cosmogenic 14C forms 14CO2. 14CH4 represents a very small fraction (< 0.3%) of the total. Assuming that the majority of in situ muogenic 14C in ice forms 14CO2, 14CO, and 14CH4, we also calculated muogenic 14C 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 14C production rates in ice and quartz currently lacks a good explanation and requires further investigation

Perfluorocyclobutane (PFC-318, &lt;i&gt;c&lt;/i&gt;-C&lt;sub&gt;4&lt;/sub&gt;F&lt;sub&gt;8&lt;/sub&gt;) in the global atmosphere

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, andspan idCombining double low line page10336 Russia are likely related to production of polytetrafluoroethylene (PTFE, Teflon ) and other fluoropolymers and fluorochemicals that are based on the pyrolysis of hydrochlorofluorocarbon HCFC-22 (span classCombining double low line inline-formula) in which span classCombining double low line inline-formula classCombining double low line inline-formula is a known by-product. The semiconductor sector, where span classCombining double low line inline-formula span classCombining double low line inline-formula is used, is estimated to be a small source, at least in South Korea, Japan, Taiwan, and Europe. 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 span classCombining double low line inline-formula span classCombining double low line inline-formula are known and though we cannot categorically exclude unknown sources, the start of significant emissions may well be related to the advent of commercial PTFE production in 1947. Process controls or abatement to reduce the span classCombining double low line inline-formula span classCombining double low line inline-formula by-product were probably not in place in the early decades, explaining the increase in emissions in the 1960s and 1970s. With the advent of by-product reporting requirements 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 span classCombining double low line inline-formula span classCombining double low line inline-formula by-product for use in the semiconductor industry where it can be easily abated, it is conceivable that emissions in developed countries were stabilized and then reduced, explaining the observed emission reduction in the 1980s and 1990s. Concurrently, production of PTFE in China began to increase rapidly. Without emission reduction requirements, it is plausible that global emissions today are dominated by China and other developing countries. We predict that span classCombining double low line inline-formula span classCombining double low line inline-formula emissions will continue to rise and that span classCombining double low line inline-formula span classCombining double low line inline-formula will become the second most important emitted PFC in terms of span classCombining double low line inline-formula equivalent emissions within a year or two. The 2017 radiative forcing of span classCombining double low line inline-formula span classCombining double low line inline-formula 0.52mWmspan classCombining double low line inline-formula) is small but emissions of span classCombining double low line inline-formula span classCombining double low line inline-formula and other PFCs, due to their very long atmospheric lifetimes, essentially permanently alter Earth's radiative budget and should be reduced. Significant emissions inferred outside of the investigated regions clearly show that observational capabilities and reporting requirements need to be improved to understand global and country-scale emissions of PFCs and other synthetic greenhouse gases and ozone-depleting substances.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

A Study of in situ cosmogenic 14C and paleoatmospheric 14CH4 from accumulating ice at Summit, Greenland

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 to limit future global warming

Empirical quantification of methane emission intensity from oil and gas producers in the Permian basin

Methane (CH _4 ) emissions from the oil and natural gas (O&G) supply chain have been demonstrated to be one of the largest anthropogenic greenhouse gas emission sources ripe for mitigation to limit near-term climate warming. In recent years, exploration and production (E&P) operators have made public commitments to reducing their greenhouse gas emission intensity, yet little empirical information has been made available in the public domain to allow an accurate comparison of their emissions performance. In this study, we utilize a series of aircraft surveys of large CH _4 point source emissions (∼10 ^1 –10 ^4 kg CH _4 hr ^−1 ) related to O&G production in the Permian Basin to enable comparison of company-level production-sector emission intensities. We calculate gas and total energy production normalized emission intensities for several of the largest E&P operators in the Permian Basin accounting for ∼85% of production within the flight region. We find differences of more than an order of magnitude in emission intensity across operators, with nearly half demonstrating a ⩾50% improvement in performance from 2019 to 2021. With the availability of such publicly attributed emissions data anticipated to increase in the future, we provide methodological insights and cautions to developing operator metrics from future empirical datasets

Strong methane point sources contribute a disproportionate fraction of total emissions across multiple basins in the United States

Understanding, prioritizing, and mitigating methane (CH4) emissions requires quantifying CH4 budgets from facility scales to regional scales with the ability to differentiate between source sectors. We deployed a tiered observing system for multiple basins in the United States (San Joaquin Valley, Uinta, Denver-Julesburg, Permian, Marcellus). We quantify strong point source emissions (>10 kg CH4 h-1) using airborne imaging spectrometers, attribute them to sectors, and assess their intermittency with multiple revisits. We compare these point source emissions to total basin CH4 fluxes derived from inversion of Sentinel-5p satellite CH4 observations. Across basins, point sources make up on average 40% of the regional flux. We sampled some basins several times across multiple months and years and find a distinct bimodal structure to emission timescales: the total point source budget is split nearly in half by short-lasting and long-lasting emission events. With the increasing airborne and satellite observing capabilities planned for the near future, tiered observing systems will more fully quantify and attribute CH4 emissions from facility to regional scales, which is needed to effectively and efficiently reduce methane emissions.Open access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Preindustrial 14CH4 indicates greater anthropogenic fossil CH4 emissions.

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