ANSTO :: Browsing by Author "Yang, B"

Browsing by Author "Yang, B"

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15th International Conference on Accelerator Mass Spectrometry
(Australian Nuclear Science and Technology Organisation, 2021-11-15) Bertuch, F; Child, DP; Fink, D; Fülöp, RH; Hotchkis, MAC; Hua, Q; Jacobsen, GE; Jenkinson, A; Levchenko, VA; Simon, KJ; Smith, AM; Wilcken, KM; Williams, AA; Williams, ML; Yang, B; Fallon, SJ; Wallner, T
On behalf of the AMS-15 Organising committee, we would like to thank you for attending the 15th International Conference on Accelerator Mass Spectrometry. Held as an online event for the first time, the 2021 conference attracted over 300 attendees with presentations delivered by colleagues and professionals from around the globe.Applications of AMS to the world’s most pressing problems/questions: A-1 : Earth’s dynamic climate palaeoclimate studies, human impacts on climate, data for climate modelling. A-2 : Water resource sustainability groundwater dating, hydrology, water quality and management A-3 : Living landscapes soil production, carbon storage, erosion, sediment transport, geomorphology. A-4 : Catastrophic natural events volcanoes, cyclones, earthquakes, tsunamis, space weather, mass extinctions. A-5 : Advancing human health metabolic and bio-kinetic studies, bomb-pulse dating, diagnostics and bio-tracing. A-6 : Challenges of the nuclear age nuclear safeguards, nuclear forensics, nuclear waste management, nuclear site monitoring, impacts of nuclear accidents. A-7 :Understanding the human story archaeology, human evolution and migration, history, art and cultural heritage A-8 : Understanding the cosmos fundamental physics, nuclear astrophysics, nuclear physics AMS Research and Development: T-1 : Novel AMS systems, components and techniques T-2 : Suppression of isobars and other interferences T-3 : Ion sourcery T-4 : New AMS isotopes T-5 : Advances in sample preparation T-6 : Data quality and management T-7 : Facility Reports (Poster Presentation only)
ANSTO Radiocarbon Laboratory: developments to meet the needs of our community
(Australian Nuclear Science and Technology Organisation, 2021-11-17) Bertuch, F; Williams, AA; Yang, B; Nguyen, TH; Varley, S; Jacobsen, GE; Hua, Q
The radiocarbon chemistry laboratories in the Centre for Accelerator Science at the Australian Nuclear Science and Technology Organisation (ANSTO) have a role providing support to AMS measurements for government organisations, industry, and academia in Australia and overseas. Over recent years the radiocarbon laboratories at ANSTO have expanded to support projects that address unique challenges which include environmental issues, the sustainable management of water resources, climate variability, ecological studies, and research into Indigenous heritage. The increase of work in these areas has seen a growing demand for processing samples of groundwater, rock art, ice cores, tree rings and Antarctic mosses. Here we will present an update of our procedures for processing a diverse range of sample types. We will also describe developments such as an automated dissolved organic carbon (DIC) extraction system for water samples, and our automated AAA pretreatment system. We will also outline our range of graphitisation systems which include a set of 24 Fe/H2 graphitisation units, 6 microconventional furnace (MCF) Fe/H2 graphitisation lines, a laser heated furnace (LHF) graphitisation system, and an Ionplus AGE-3 graphitisation system (owned by UNSW). Our MCF and conventional graphitisation lines have been designed to handle and reliably produce graphite targets containing as little as 5 μg and 10ugC of carbon respectively), making the graphitisation of minute carbon samples from rock art and ice cores possible.
The ANSTO – University of Wollongong in-situ 14C extraction laboratory
(Elsevier, 2019-01-01) Fülöp, RH; Fink, D; Yang, B; Codilean, AY; Smith, AM; Wacker, L; Levchenko, VA; Dunai, TJ
We present our first 14C in-situ results for calibration and system blanks from the recently completed Australian Nuclear Science and Technology Organisation (ANSTO) – University of Wollongong (UOW) in-situ 14C extraction system. System performance parameters and quality is evidenced by low 14C blanks and good reproducibility for multiple targets from different reference materials. The 14C extraction scheme exploits the high temperature phase transformation of quartz to cristobalite in order to quantitatively extract the carbon as CO2. The in-situ 14C extraction system comprises three independently operated and modular units that are used for initial in-vacuo removal of meteoric 14C, followed by offline high-temperature heating of quartz to release trapped cosmogenic in-situ 14C, and finally CO2 gas purification and mass measurement. The design allows for rapid sample throughput of about 6 samples per week with samples masses ranging between 0.5 and 4 g of clean quartz. Other features include single-pass catalytic oxidation using mixed copper (I,II) oxide as catalyst, use of UHV-compatible components and of vacuum annealed copper tubing. We present results for sets of purified quartz samples prepared from CRONUS-A, CRONUS-R and CRONUS-N inter-comparison materials, with final averages consistent with published values. Following extraction and cleaning, CO2 gas aliquots for some of the samples were analysed using the ETH Zürich CO2 gas ion source at the ETH MICADAS AMS facility in addition to CO2 being graphitised using the ANSTO laser-heated graphitisation micro-furnace and then analysed on ANSTO’s ANTARES AMS facility. System blanks using either CO2 or graphite ion-sources at both facilities are on the order of ∼1 × 104 atoms. © 2018 Elsevier B.V.
Characterization of in situ cosmogenic 14CO production, retention and loss in firn and shallow ice at summit, Greenland
(Copernicus Publications, 2024-07-25) Hmiel, B; Petrenko, VV; Buizert, C; Smith, AM; Dyonisius, MN; Place, PF; Yang, B; Hua, Q; Beaudette, R; Severinghaus, JP; Harth, CM; Weiss, RF; Davidge, L; Diaz, M; Pacicco, M; Menking, JA; Kalk, M; Faïn, X; Adolph, A; Vimont, I; Murray, LT
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. The 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 timescale 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 % yr−1. 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 14CO production rates in ice via the muon mechanisms and allowing for narrowing constraints on these production rates. © Author(s) 2024. This work is distributed under the Creative Commons Attribution 4.0 License.
A cold finger cooling system for the efficient graphitisation of microgram-sized carbon samples
(Elsevier Science BV, 2013-01-01) Yang, B; Smith, AM; Hua, Q
At ANSTO, we use the Bosch reaction to convert sample CO2 to graphite for production of our radiocarbon AMS targets. Key to the efficient graphitisation of ultra-small samples are the type of iron catalyst used and the effective trapping of water vapour during the reaction. Here we report a simple liquid nitrogen cooling system that enables us to rapidly adjust the temperature of the cold finger in our laser-heated microfurnace. This has led to an improvement in the graphitisation of microgram-sized carbon samples. This simple system uses modest amounts of liquid nitrogen (typically <200 mL/h during graphitisation) and is compact and reliable. We have used it to produce over 120 AMS targets containing between 5 and 20 mu g of carbon, with conversion efficiencies for 5 mu g targets ranging from 80% to 100%. In addition, this cooling system has been adapted for use with our conventional graphitisation reactors and has also improved their performance. © 2013, Elsevier Ltd.
A cold finger cooling system for the efficient graphitisation of microgram-sized carbon samples
(12th International Conference on Accelerator Mass Spectrometry (AMS-12), 2011-03-24) Yang, B; Smith, AM; Hua, Q
At ANSTO we use the Bosch reaction to convert sample CO2 to graphite for production of our radiocarbon AMS targets. Key to the efficient graphitisation of ultra-small samples is the type of iron catalyst and the effective trapping of water vapour in a ‘cold finger’ during the reaction. We have developed a simple liquid nitrogen cooling system that enables us to rapidly adjust the cold finger temperature in our laser-heated ‘microfurnace’, optimised for the graphitisation of microgram-sized carbon samples. This system is used to firstly transfer the CO2 into the microfurnace, to maintain the cold finger at -80°C for ~ 5 minutes while the CO2 is converted to CO and then at -160°C for ~ 25 minutes for the remainder of the reaction as the CO is converted to graphite. It comprises a machined aluminium cylinder mounted in the insulated cap of a 600 ml Dewar. The lower end is submerged in liquid nitrogen (LN2). The upper end has a smaller diameter which is wound with an electric heating element and is provided with a thermocouple and a central hole into which the cold finger is inserted. Electrical power to the heater is adjusted by PID control, permitting the cold finger temperature to be adjusted over the range -50°C to -160°C at rates of up to 40°C/min. This simple system uses modest amounts of LN2 (typically < 0.2 L/hr during graphitisation) and is compact and reliable. We have used it to produce over 120 AMS targets containing between 5 and 20 μg of carbon, with conversion efficiencies for 5 μg targets of typically 90-100%. We are currently modifying this cooling system for use with our conventional graphitisation reactors. Copyright (c) 2011 AMS12
Constraining the evolution of the fossil component of the global methane budget since the pre-industrial using 14C measurements in firn air and ice cores
(American Geophysical Union, 2018-12-13) Hmiel, B; Dyonisius, MN; Petrenko, VV; Buizert, C; Smith, AM; Place, PF; Etheridge, DM; Harth, CM; Beaudette, R; Hua, Q; Yang, B; Vimont, I; Brook, EJ; Weiss, RF; Severinghaus, JP
Radiocarbon of atmospheric methane (14CH4) is much less studied than radiocarbon of atmospheric carbon dioxide (14CO2) yet has potential to serve as an unambiguous indicator of the balance between fossil and contemporaneous sources of this important greenhouse gas. Few measurements of atmospheric 14CH4 exist before the late 20th century. We present measurements of past atmospheric 14CH4 in firn air and ice at Summit, Greenland. These data provide a record of atmospheric 14CH4 from 2013 back to ~1750 CE. Results have been corrected for a small amount of cosmogenic in-situ production of 14CH4 within the ice crystal lattice. A firn gas transport model was used to simulate the transport of gases through the porous firn column and into fully closed ice, and an inverse model reconstructed the firn air and ice 14CH4 data into an atmospheric history. Our results from the mid-late 20th century agree with the only previously published measurements of 14CH4 from firn air (at Law Dome, Antarctica). Pre-industrial 14CH4 samples agree with the INTCAL13 14CO2 history within uncertainties, indicating that natural geologic methane emissions are very low and have been commonly overestimated in the global methane budget. From ~1880 to ~1950 CE, the atmospheric 14CH4 activity decreased via the Suess effect, indicating a 14 ± 2% fossil CH4 source in the mid 1900’s. After mid-century, despite increasing anthropogenic fossil CH4 emissions, the 14CH4 activity began increasing due to atmospheric nuclear bomb testing and direct 14CH4 emissions from nuclear power plants.
The contribution of geologic emissions, thawing permafrost and methane hydrates to the global methane budget – perspective from ice core records
(American Geophysical Union, 2018-12-13) Dynonisius, MN; Petrenko, VV; Smith, AM; Beck, J; Schmitt, J; Menking, JA; Shackleton, SA; Hmiel, B; Vimont, I; Hua, Q; Yang, B; Seth, B; Bock, M; Beaudette, R; Harth, CM; Baggenstos, D; Bauska, TK; Rhodes, RH; Brook, EJ; Fischer, H; Severinghaus, JP; Weiss, RF
Studies of methane (CH4) mole fraction and isotopes from trapped air in ice cores provide a long-term perspective on the natural CH4 budget. Among the CH4 isotopes, 14CH4 is unique in providing a definitive top-down constraint on the total fossil CH4 emissions from old carbon reservoirs (marine hydrates, permafrost, natural geologic seeps). We present new measurements of 14CH4 throughout most of the Last Deglaciation (≈15-8ka). Our 14CH4 data show that 14C-depleted CH4 sources (marine hydrates, geologic seeps and old permafrost) were not significant contributors to the deglacial CH4 rise. As the relatively large deglacial global warming (≈4oC, with warming further amplified at high latitudes) did not trigger CH4 emissions from old carbon reservoirs, such emissions in response to future warming also appear unlikely. Our results also strengthen the suggestion from an earlier study (Petrenko et al. 2017) that natural geologic emissions of CH4 are much lower (less than 15 Tg CH4 yr-1, 95% confidence) than recent bottom-up estimates (54-60 Tg CH4 yr-1) (Etiope 2015; Cias et al. 2013) and that, by extension, estimates of present-day total anthropogenic fossil CH4 emissions are likely too low.
Conventionally-heated miniaturised furnace for graphitisation of microgram-sized carbon samples
(University of Arizona, 2016-01-01) Yang, B; Smith, AM
A new type of miniaturized, externally heated graphitization reaction furnace, the microconventional furnace (MCF), was constructed following our development of the laser heated furnace (LHF). The MCF is comprised of a gas reactor, a cold finger cooling system, and a compact resistive heater, which can raise the temperature of the hot finger to 850°C. The gas reactor is provided with three integrated valves to connect with the hydrogen/vacuum manifold, to isolate the reactor, and to connect with sample vessels. We made two types of MCF: the type 1 furnace (volume of 0.9 mL), with an integral stainless steel cold finger, and the type 2 furnace (volume from 1.3 to 10 mL), with a changeable glass cold finger. The MCF is designed for above atmospheric pressure (up to 2500 mbar) operation to decrease the overall graphitization time and improve the carbon yield. The MCF provides an effective solution for producing graphite from carbon dioxide (CO 2 ) sample gas from 5 to 2000 µg of carbon with only 0.083 μg of 100 pMC extraneous carbon added. Cross-contamination tests show that the MCFs have no memory effect from previous samples. © 2016 by the Arizona Board of Regents on behalf of the University of Arizona
Delineating the first few seconds of supramolecular self-assembly of mesostructured titanium oxide thin films through time-resolved small angle x-ray scattering
(American Chemical Society, 2008-10-07) Luca, V; Bertram, WK; Sizgek, GD; Yang, B; Cookson, DJ
The early stages of evaporation induced self-assembly of titanium oxide mesophases from a precursor solution containing TiCl4 and the Pluronic triblock copolymer F-127 in HCl-water-ethanol solution have been studied using time-resolved SAXS techniques. Two experimental protocols were used to conduct these experiments. In one of these, the precursor solution was pumped around a closed loop as solvent was allowed to evaporate at a constant humidity-controlled rate. In the second protocol, a film of precursor solution was measured periodically as it dried completely to a residue under a stream of dry air. This permitted the detailed monitoring of changes in solution chemistry as a function of the elimination of volatile components followed by the actual drying process itself. The SAXS data were modeled in terms of two Guinier radii for soft nanoparticles while a broad Gaussian feature in the scatter profiles was accounted for by particle-article scattering interference due to close packing. For the initial precursor solution, one Guinier radius was found to be about 17 (A) over circle while the other ranged from 4 to 11 (A) over circle. Changing the rate of evaporation affected the two radii differently with a more pronounced effect on the smaller particle size range. Analysis gave an interparticle distance in the range 55-80 (A) over circle for the initial precursor solution which decreased steadily at both of the humidities investigated as evaporation proceeded and the particle packing increased. These results represent the first attempts to monitor in a precise fashion the growth of nano building blocks during the initial stages of the self-assembly process of a titanium oxide mesophase. © 2008, American Chemical Society
Early results from the ANSTO/NIWA 14C of atmospheric methane program
(12th International Conference on Accelerator Mass Spectrometry (AMS-12), 2011-03-24) Smith, AM; Brailsford, G; Yang, B; Bromley, T; Martin, R
development and proving of the laser heated microfurnace we have used it to prepare 45 samples of ~ 16 μg of carbon. These comprised CO2, derived from atmospheric methane, frozen back into glass breakseals following measurement for δ13C at NIWA. There were three sample sets: 15 from Baring Head, NZ (BHD), collected each ~ 15 days between March and September 2009, 9 from Arrival Heights, Antarctica (SCT), collected each ~ 41 days between February 2008 and January 2009, plus 21 samples taken along a Pacific Ocean voyage from Nelson (NZ) – Osaka (Japan) in December 2005 (FTW). All samples were measured to better than 1% precision, sufficient to reveal a 14CH4 signal. The BHD set shows significant temporal variation in 14C for baseline air passing over the Southern Ocean, whereas the SCT set shows a lesser variation for Antarctic air. The FTW set covers a S-N transect across the Pacific Ocean, showing the influence of the ITCZ (5°-10° N) and different meteorological conditions on the concentration, δ13C and Δ14C of CH4 and demonstrates that CH4 is not well mixed. Graphitisation reactions averaged 32 min with 0.7 mg of Fe, reduced from Fe2O3, as the catalyst. The samples, blanks and standards were measured in two 10 minute blocks; some were measured again to improve statistics. Average 13C4+ currents per microgram of carbon were 13, 4 and 2 nA/μg for each 10 min block. Similarly-sized targets prepared in the conventional furnace with Fe2O3 gave 8, 5 and 2 nA/μg for each 10 min block. Graphitisation efficiencies were typically 90-100% for microfurnace samples, compared with 37-84% for conventional furnace samples. Subsequent examination by microscope showed that the cesium beam was well-centred on the 1 mm diameter recess and that effectively all C/Fe was sputtered, leading to a (minimum) estimation of ~4% overall AMS measurement efficiency. Copyright (c) 2011 AMS12
Exploring sediment dynamics from source to sink in the Murray-Darling basin using cosmogenic 14C, 10Be, and 26Al
(Australasian Quaternary Association Inc., 2018-12-10) Fülöp, RH; Codilean, AT; Marx, SK; Cohen, TJ; Fink, D; Yang, B; Smith, AM; Wilcken, KM; Fujioka, T; Wacker, L; Dunai, TJ
The relatively short half-life of 14C, namely, 5730 years, means that, compared to the other cosmogenic nuclides, it is substantially more sensitive to short term variations in process rates. Both the erosion of steep mountains and the dynamics of sediment transport, storage and recycling occur over timescales that are too short to be detectable by the cosmogenic nuclides that are currently used routinely, namely 10Be and 26Al. In situ 14C on the other hand is ideally suited for these short timescales, and used in combination with 26Al and 10Be, it will allow for rapid fluctuations in process rates and/or the relatively short timescales that characterise sediment transfer and storage to be measured accurately. The above make in situ 14C an important addition to the cosmogenic radionuclide toolkit. We present results of in situ cosmogenic 14C system blank and calibration sample measurements obtained with the recently established ANSTO/UOW in situ 14C extraction system. The 14C extraction scheme follows the design of the University of Cologne, which exploits the phase transformation of quartz to crystobalite to quantitatively extract the carbon as CO2. Offline high-temperature furnace extraction allows a relative rapid sample throughput and can accommodate samples ranging between 0.5 to 4 grams of clean quartz. Following extraction and isolation, the CO2gas is graphitised using a micro-furnace and then measured using AMS similarly to routine small radiocarbon samples. We also present results of 14C, 26Al, and 10Be analyses from sediment samples collected from Australia’s largest river system, the Murray-Darling basin. We use the downstream changes in the ratios of the three radionuclides in samples collected at key locations along the rivers to quantify sediment mixing and sediment storage times in the river basin. Substantial 26Al/10Be ‘burial’ signal is observed in downstream Murray and Darling samples, while in situ 14C suggests complex burial-exposure histories in these samples. This could have implication of interpreting geochemical proxies at the outlet of Murray-Darling Basin for identification of paleoclimate driven sediment sources (i.e. Monsoon vs. Westerlies). © The Authors
Graphitisation & measurement of microgram radiocarbon samples at ANSTO
(Australian Nuclear Science and Technology Organisation, 2021-11-17) Smith, AM; Hua, Q; Varley, S; Williams, AA; Yang, B
The Centre for Accelerator Science (CAS) at ANSTO has been providing radiocarbon analyses for the user community and internal projects for two and a half decades. Early on, there was a need to develop the measurement capability for samples containing just tens of micrograms of carbon [1, 2]. We have continued to develop this capability since. At first effort was directed at optimising our ‘conventional’ graphitisation furnaces [3]. These have a minimum reaction volume of ~ 2.5 mL and reduce CO₂ to graphite over an Fe catalyst at 600 °C in an excess of hydrogen. CAS operates a bank of 24 conventional furnaces which provide for the bulk of our sample graphitisation for samples containing > 5 μg of carbon. In 2003 we began developing a novel, miniaturised graphitisation furnace which used a focused infrared laser to heat the Fe catalyst in a quartz crucible, with the temperature measured indirectly by infrared thermometry [4]. The prototype unit had an internal reaction volume of ~0.5 mL including pressure transducer and the two subsequent furnaces ~ 0.3 mL. These small volumes allow a higher initial pressure for small amounts of CO₂ , improving the efficiency of conversion to graphite. Efficient trapping of the water vapour produced during the reaction and careful selection of the catalyst are also key to optimising graphitisation of small samples [5, 6]. By localising the heated region within the reaction volume, the addition of extraneous carbon is minimised in these furnaces and samples containing just 1-2 μg of carbon are routinely prepared. The laser heated furnaces (LHF) are preferred for processing the very small samples derived from our ¹⁴ C in situ program [7]. The fabrication approach developed for the LHF was adapted to a new type of miniaturised furnace we call micro-conventional furnaces (MCF) [8]. These furnaces have a minimum reaction volume of ~ 0.9 mL with a small tube furnace to heat the catalyst. Variable temperature cold traps have been developed to optimise sample processing with samples as small as 5 μg of carbon routinely prepared. The MCF are used extensively in conjunction with ¹⁴ C measurements of CO, CO₂ and CH₄ derived from ice core and firn air samples. We present an overview of micro-sample graphitisation and measurement at CAS.
Ice core and firn air 14CH4 measurements from preindustrial to present suggest that anthropogenic fossil CH4 emissions are underestimated
(Copernicus GmbH, 2019-04-08) Hmiel, B; Petrenko, VV; Dyonisius, MN; Buizert, C; Smith, AM; Place, PF; Harth, CM; Beaudette, R; Hua, Q; Yang, B; Vimont, I; Schmitt, J; Etheridge, DM; Fain, X; Weiss, RF; Severinghaus, JP
Concentrations of atmospheric methane (CH4), a potent greenhouse gas, have more than doubled since preindustrial times yet its contemporary budget is incompletely understood, with substantial discrepancies between global emission inventories and atmospheric observations (Kirschke et al., 2013; Saunois et al., 2016). Radiomethane (14CH4) can distinguish between fossil emissions from geologic reservoirs (radiocarbon free) and contemporaneous biogenic sources, although poorly constrained direct 14CH4 emissions from 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 Tg CH4/yr, (Saunois et al., 2016; Schwietzke et al., 2016)) are partitioned between anthropogenic sources (such as fossil fuel extraction and consumption) and natural sources (such as geologic seeps); emission inventories suggest the latter accounts for ~50-60 Tg CH4/yr (Etiope, 2015; Etiope et al., 2008). Geologic emissions were recently shown to be much smaller at the end of the Pleistocene ~11,600 years ago (Petrenko et al. 2017); However, this period is an imperfect analog for the present day due to the much larger terrestrial ice sheet cover, lowered sea level, and more extensive permafrost. We use preindustrial ice core measurements of 14CH4 to show that natural fossil CH4 emissions to the atmosphere are ~1.7 Tg CH4/yr, with a maximum of 6.1 Tg CH4/yr (95% confidence limit), an order of magnitude smaller than estimates from global inventories. This result suggests that contemporary anthropogenic fossil emissions are likely underestimated by a corresponding amount (~48-58 Tg CH4/yr, or ~25-33% of current estimates). © Author(s) 2019. CC Attribution 4.0 license.
An improved method for atmospheric 14CO measurements
(Copernicus Publications, 2021-03-15) Petrenko, VV; Smith, AM; Crosier, EM; Kazemi, R; Place, PF; Colton, A; Yang, B; Hua, Q; Murray, LT
Important uncertainties remain in our understanding of the spatial and temporal variability of atmospheric hydroxyl radical concentration ([OH]). Carbon-14-containing carbon monoxide (14CO) is a useful tracer that can help in the characterization of [OH] variability. Prior measurements of atmospheric 14CO concentration ([14CO] are limited in both their spatial and temporal extent, partly due to the very large air sample volumes that have been required for measurements (500–1000 L at standard temperature and pressure, L STP) and the difficulty and expense associated with the collection, shipment, and processing of such samples. Here we present a new method that reduces the air sample volume requirement to ≈90 L STP while allowing for [14CO] measurement uncertainties that are on par with or better than prior work (≈3 % or better, 1σ). The method also for the first time includes accurate characterization of the overall procedural [14CO] blank associated with individual samples, which is a key improvement over prior atmospheric 14CO work. The method was used to make measurements of [14CO] at the NOAA Mauna Loa Observatory, Hawaii, USA, between November 2017 and November 2018. The measurements show the expected [14CO] seasonal cycle (lowest in summer) and are in good agreement with prior [14CO] results from another low-latitude site in the Northern Hemisphere. The lowest overall [14CO] uncertainties (2.1 %, 1σ) are achieved for samples that are directly accompanied by procedural blanks and whose mass is increased to ≈50 µgC (micrograms of carbon) prior to the 14C measurement via dilution with a high-CO 14C-depleted gas. © Author(s) 2021. This work is distributed under the Creative Commons Attribution 4.0 Licence.
Investigation of OC and EC fractions of aerosol samples in Sydney area by radiocarbon analysis
(Australian Nuclear Science and Technology Organisation, 2021-11-17) Yang, B; Keywood, MD; Reisen, F; Smith, AM; Levchenko, VA
Secondary Organic Aerosols (SOA) can be a major component of atmospheric PM.2.5 pollution, emitted from natural and anthropogenic sources. SOA is formed by the oxidation of volatile organic compounds (VOC) which have biogenic and anthropogenic sources. Measurement of the radiocarbon activity of SOA allows to discriminate between these sources, as biogenic sources have a near-modern activity and anthropogenic sources are generally depleted in ¹⁴ C. As part of the Sydney Particle Study [1,2], aerosol samples were collected on quartz filters using a high volume sampler fitted with a PM2.5 size selective inlet during the summer months of 2011 and autumn months of 2012. In order to estimate the apportionment of the SOA sources, we measured the radiocarbon content of organic carbon (OC) and elemental carbon (EC) fractions, using the novel method described below. We combusted strips (90 × 35 mm) of the quartz filters strip inside a quartz tube filled with high purity oxygen at ~300 mbar at 375°C to collect the OC fraction and then at 780°C to collect the EC fraction. CO₂ gas produced during each combustion was collected in a cold trap at -170°C, volumetrically measured and transferred into a Micro Conventional Furnaces (MCF) [3] for graphitisation. This method was shown to be reproducible for EC and OC filter densities from the same filter. We processed 25 air filters in this way to produce 50 samples for Accelerator Mass Spectroscopy (AMS) measurement with an average of 58 μg carbon (range 10 μg to 220 μg). Our densities compared well with OC and EC densities obtained using a standard thermal desorption method at CSIRO [2]. We combined the measured radiocarbon activity with sophisticated chemical transport modelling, using the EC tracer method [4] to determine SOA. Levoglucosan was used as a tracer to allow for biomass burning events. Our results suggested that i) biogenic SOA comprised around 50% of the SOA in summer and autumn, ii) higher radiocarbon activities for OC are associated with higher SOA concentrations, supporting the model theory [1] that that biogenic VOCs are an important contributor to SOA in the Sydney airshed, iii) the formation of SOA involves both anthropogenic and biogenic VOC, iv) the lowest EC and OC radiocarbon activities were for summer mornings, indicating high fossil fuel carbon (i.e. vehicle emissions). Afternoons in summer and autumn displayed the highest ratios, indicating low fossil fuel carbon. © The Authors
Investigation of the combustion of methane using CuO for radiocarbon dating
(Elsevier, 2019-09-15) Yang, B; Smith, AM
For the combustion of methane (CH4) gas to carbon dioxide (CO2), we investigated the use of copper oxide (CuO) as the source of oxygen, using our type 2 Micro Conventional Furnaces (MCF-II), traditionally used for the reduction of CO2 to graphite for AMS measurement Yang and Smith, 2017 [1]. Experiments showed that both graphite and CH4 can be oxidised to CO2 rapidly at a temperature at 780 °C. The reaction is complete within just a few minutes for graphite and within about one hour for CH4 gas. However, this method is only suitable for combustion of CH4 when the concentration >3% due to the small internal volume of MCF-II. To combust gases of lower CH4 concentration, we installed a gas circulation loop with additional components including 1) a novel, newly designed MCF-III with a dual tube furnace for heating 6 mm OD quartz tubes up to 850 °C; 2) a gas circulating unit comprising a miniature diaphragm pump and flow meter along with a needle valve for adjusting gas flow rate; 3) differently sized gas storage tubes and bags, permitting optimisation of the carbon sample size; 4) a water trap and miniature CO2 gas traps −65 °C and −150 °C respectively Yang et al., 2013 [2]. This system is also suitable for collecting CO2 from air at atmospheric concentrations. It also has the flexibility to assemble a specific gas trapping/combustion system to suit the composition of individual gas samples. We report on the early performance with some samples and our evaluation of the cross contamination between CO2 and CH4 based AMS measurement of a set of mixing gas CO2/CH4/N2 samples. Crown Copyright © 2018 Published by Elsevier B.V.
Laser-heated microfurnace: gas analysis & graphite morphology
(Cambridge University Press, 2009-06-04) Smith, AM; Yang, B; Hua, Q; Mann, M
preparing ultra-small graphite samples from CO2 at the ~5 μg of carbon level (Smith et al. 2006, 2007, 2008). Recent effort has focused on automation using a LABview interface, which has permitted feedback control of the catalyst temperature as the reaction proceeds and logging of reaction parameters. Additionally, an automatic system has been developed to control the temperature of the cold finger for trapping CO2 (–196°C), trapping H2O (–80°C) and releasing these gases (25°C) during sample transfer and during the reaction. We have utilized a quadrupole mass spectrometer to study the gas composition during the reaction, in order to better understand the underlying chemical reactions for such small samples and to better estimate the overall efficiency of the process. Early results show that all CO2 is converted to CO by reduction on the iron catalyst within a few minutes of applying laser power. The reaction pressure stabilizes after ~20 minutes; however, some CO is not converted to graphite. The cold trap temperature of –80°C is effective at trapping H2O so there is little CH4 production. We have trialled a number of different iron catalysts (Cerac -325, Sigma Aldrich -400 and 25 nm Fe nanopowder) as well as Fe2O3 (reduced in situ to Fe) and have studied the graphite morphology by scanning electron microscopy (SEM). There is a marked difference in morphology with catalyst type; however, each graphite performs well in the cesium sputter ion source of the ANTARES AMS facility. These developments allow us to systematically optimize the performance of the apparatus and to develop a second generation device.
Law Dome 14CH4 measurements confirm revised fossil methane emissions estimates
(Australian Nuclear Science and Technology Organisation, 2021-11-17) Etheridge, DM; Petrenko, VA; Smith, AM; Neff, PD; Hmiel, B; Trudinger, CM; Crosier, EM; Thornton, DP; Langefelds, RL; Jong, LM; Harth, CM; Mitrevski, B; Buizert, C; Yang, B; Weiss, RF; Severinghaus, JP
Methane is a powerful greenhouse gas and has significant roles in the chemistry of the atmosphere. Its global concentration has risen by 240% since 1750 AD. Atmospheric 14CH4 is an independent and potentially unambiguous tracer of fossil CH4 emissions from anthropogenic and natural geologic sources, however 14C from nuclear weapons tests and 14CH4 from nuclear power plants complicate its interpretation after the late 1950s. Measurements before then rely on air extracted from polar ice and firn. Hmiel et al. (Nature, 2020) measured 14CH4 in air extracted from firn and ice in Greenland and Antarctica and found that the natural global fossil CH4 source is very small (<6 Tg CH4 yr-1). This is inconsistent with bottom-up geological CH4 emissions estimates (40-60 Tg CH4 yr-1) and implies a significant upward revision of anthropogenic fossil source emissions, emphasising the need for further measurements. We present new 14CH4 measurements of air extracted from the high accumulation site DE08-OH on the Law Dome ice sheet in 2018/19, including firn air to 81 m depth and large ice samples combined from parallel ice cores to 240 m. Measurements of trace gases confirm that the samples were uncontaminated and only minor corrections are required for sample processing. The correction for cosmogenic in-situ production of 14CH4 is very small at DE08-OH due to its high accumulation rate and relatively low elevation. The new 14CH4 results compare closely with the previous measurements from the other sites. An atmospheric 14CH4 history is reconstructed from inverse modelling of the combined ice and firn data. The pre-industrial 14CH4 level is almost identical to that expected from contemporaneous biogenic sources, confirming very minor natural fossil CH4 emissions. 14CH4 decreases to a minimum in about 1940 as anthropogenic fossil methane is emitted followed by an increase during the nuclear era from 1950 to present. The record since the 1950s would allow the evolution of the anthropogenic fossil source to be quantified when improved nuclear 14CH4 emissions estimates become available. The larger emissions from anthropogenic fossil sources implied by this result highlight opportunities for methane emissions reductions. © The Authors
Law Dome 14CH4 measurements confirm revised fossil methane emissions estimates
(American Geophysical Union (AGU), 2021-12-17) Etheridge, DM; Petrenko, VA; Smith, AM; Neff, PD; Hmiel, B; Trudinger, CM; Crosier, EM; Thornton, DP; Langenfelds, RL; Jong, LM; Harth, CM; Mitrevski, B; Buizert, C; Yang, B; Weiss, RF; Severinghaus, JP
Methane is a powerful greenhouse gas and has significant roles in the chemistry of the atmosphere. Its global concentration has risen by 240% since 1750 AD. Atmospheric 14CH4 is an independent and potentially unambiguous tracer of fossil CH4 emissions from anthropogenic and natural geologic sources, however 14C from nuclear weapons tests and 14CH4 from nuclear power plants complicate its interpretation after the late 1950s. Measurements before then rely on air extracted from polar ice and firn. Hmiel et al. (Nature, 2020) measured 14CH4 in air extracted from firn and ice in Greenland and Antarctica and found that the natural global fossil CH4 source is very small (<6 Tg CH4 yr-1). This is inconsistent with bottom-up geological CH4 emissions estimates (40-60 Tg CH4 yr-1) and implies a significant upward revision of anthropogenic fossil source emissions, emphasising the need for further measurements. We present new 14CH4 measurements of air extracted from the high accumulation site DE08-OH on the Law Dome ice sheet in 2018/19, including firn air to 81 m depth and large ice samples combined from parallel ice cores to 240 m. Measurements of trace gases confirm that the samples were uncontaminated and only minor corrections are required for sample processing. The correction for cosmogenic in-situ production of 14CH4 is very small at DE08-OH due to its high accumulation rate and relatively low elevation. The new 14CH4 results compare closely with the previous measurements from the other sites. An atmospheric 14CH4 history is reconstructed from inverse modelling of the combined ice and firn data. The pre-industrial 14CH4 level is almost identical to that expected from contemporaneous biogenic sources, confirming very minor natural fossil CH4 emissions. 14CH4 decreases to a minimum in about 1940 as anthropogenic fossil methane is emitted followed by an increase during the nuclear era from 1950 to present. The record since the 1950s would allow the evolution of the anthropogenic fossil source to be quantified when improved nuclear 14CH4 emissions estimates become available. The larger emissions from anthropogenic fossil sources implied by this result highlight opportunities for methane emissions reductions.

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