ESTABLISHING WATER SAMPLE PROTOCOLS FOR RADIOCARBON ANALYSIS AT LAC-UFF, BRAZIL

ABSTRACT Since the establishment of the first radiocarbon accelerator mass spectrometry facility in Latin America in 2009, the Radiocarbon Laboratory team of Universidade Federal Fluminense (LAC-UFF) has worked to improve sample preparation protocols and increase the range of environmental matrices to be analyzed. We now present the preliminary results for DIC sample preparation protocols. The first validation tests include background evaluation with pMC value (0.35 ± 0.04) using bicarbonate dissolved in water. We also analyzed surface seawater resulting in pMC value (101.38 ± 0.38) and a groundwater previously dated from LEMA AMS-Laboratory with pMC value (12.30 ± 0.15).

A novel sampling system for radiocarbon measurements of atmospheric methane

<p>Radiocarbon in atmospheric methane (Δ<sup>14</sup>CH<sub>4</sub>) is a powerful tracer of fossil methane emissions and can be used to attribute methane emissions to fossil or biogenic sources. However, few Δ<sup>14</sup>CH<sub>4 </sub>measurements are reported since 2000<sup>1,2</sup>, due to challenges in sampling enough carbon for <sup>14</sup>C measurements and in assessing the influence of <sup>14</sup>C emissions from nuclear power plants on the <sup>14</sup>C observations.</p><p>At Imperial College London we addressed the sampling limitation by developing a unique sampling system that separates carbon at the point of sampling and uses small traps of molecular sieves. Collection of a sample is made by three main steps: 1) removal of CO<sub>2</sub> and CO from air, 2) combustion of CH<sub>4</sub> into CO<sub>2</sub> and 3) adsorption of the combustion-derived CO<sub>2</sub> onto the molecular sieve trap. <sup>14</sup>C analysis of our samples was carried out at the accelerator mass spectrometry facility at UCI. This novel system has been used for collection of samples in central London and has been made portable for collection of samples in different settings. </p><p>Here we describe the system and report the evaluation of the measurement uncertainty and the processing blank. We achieved a measurement precision of 6 ‰, which is similar to or better than the reported precision of the most recent observations<sup>1,3</sup>.</p><p><sup>1</sup> Townsend‐Small et al JGR 117(D7) 2012</p><p><sup>2</sup> Sparrow et al Sci. Adv 4(1) 2018</p><p><sup>3</sup> Espic et al Radiocarbon 61( 5) 2019</p>

RADIOCARBON IN DISSOLVED ORGANIC CARBON BY UV OXIDATION: PROCEDURES AND BLANK CHARACTERIZATION AT NOSAMS

ABSTRACT This study describes a procedural blank assessment of the ultraviolet photochemical oxidation (UV oxidation) method that is used to measure carbon isotopes of dissolved organic carbon (DOC) at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS). A retrospective compilation of Fm and δ13C results for secondary standards (OX-II, glycine) between 2009 and 2018 indicated that a revised blank correction was required to bring results in line with accepted values. The application of a best-fit mass-balance correction yielded a procedural blank of 22.0 ± 6.0 µg C with Fm of 0.30 ± 0.20 and δ13C of –32.0 ± 3.0‰ for this period, which was notably higher and more variable than previously reported. Changes to the procedure, specifically elimination of higher organic carbon reagents and improved sample and reactor handling, reduced the blank to 11.0 ± 2.75 µg C, with Fm of 0.14 ± 0.10 and δ13C of –31.0 ± 5.5‰. A thorough determination of the entire sample processing blank is required to ensure accurate isotopic compositions of seawater DOC using the UV oxidation method. Additional efforts are needed to further reduce the procedural blank so that smaller DOC samples can be analyzed, and to increase sample throughput.