Browsing by Author "Kazemi, R"

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    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.
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    Using atmospheric 14CO to provide additional constraints for global OH: first results from a new approach and potential for future measurements
    (American Geophysical Union, 2018-12-13) Petrenko, VV; Murray, LT; Smith, AM; Crosier, EM; Colton, A; Hua, Q; Yang, B; Kazemi, R; Usoskin, IG; Poluianov, S
    The primary source of 14C-containing carbon monoxide (14CO) in the atmosphere is via 14C production from 14N by secondary cosmic rays, and the primary sink is removal by hydroxyl radicals (OH). Variations in the global abundance of 14CO that are not explained by variations in 14C production are mainly driven by variations in the global abundance of OH. Monitoring OH variability via methyl chloroform is becoming increasingly difficult as methyl chloroform abundance is continuing to decline. Measurements of atmospheric 14CO have previously been successfully used to infer OH variability. However, these measurements are currently only continuing at one location (Baring Head, New Zealand), which is insufficient to infer global trends. We propose to restart global 14CO monitoring with the aim of providing an additional constraint on OH variability. A new analytical system for 14CO sampling and measurements has been developed, allowing for a ten-fold reduction in the required sample air volumes and simplified field logistics. The first 14CO measurements from Mauna Loa Observatory show good agreement with prior measurements in the same latitude band. Preliminary work with a state-of-the-art chemical transport model is exploring sensitivity of 14CO at potential sampling locations to changes in production rates and OH.
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    Using atmospheric 14CO to provide additional constraints for global OH: results from a new approach and potential for future measurements
    (Copernicus GmbH, 2019-04-10) Petrenko, VV; Murray, LT; Crosier, EM; Colton, A; Hua, Q; Smith, AM; Yang, B; Kazemi, R; Neff, PD; Etheridge, DM; Usoskin, IG; Poluianov, S
    The primary source of 14C-containing carbon monoxide (14CO) in the atmosphere is via 14C production from 14N by secondary cosmic rays, and the primary sink is removal by hydroxyl radicals (OH). Variations in the global abundance of 14CO that are not explained by variations in 14C production are mainly driven by variations in the global abundance of OH. Monitoring OH variability via methyl chloroform is becoming increasingly difficult as methyl chloroform abundance is continuing to decline. Measurements of atmospheric 14CO have previously been successfully used to infer OH variability. However, these measurements have only continued at one location (Baring Head, New Zealand), which is insufficient to infer global trends. We propose to restart global 14CO monitoring with the aim of providing an additional constraint on OH variability. A new analytical system for 14CO sampling and measurements has been developed, allowing for a ten-fold reduction in the required sample air volumes and simplified field logistics. The first 14CO measurements from Mauna Loa Observatory show good agreement with prior measurements in the same latitude band. Preliminary work with a state-of-the-art chemical transport model is exploring sensitivity of 14CO at potential sampling locations to changes in production rates and OH. This presentation will also provide an update on a project which aims to improve the understanding of long-term OH variability via reconstructing a 150-year history of atmospheric 14CO from ice cores at Law Dome, Antarctica. Sampling of the ice and on-site extractions of large volumes of ancient air were in progress during December 2018 – January 2019. © Author(s) 2019. CC Attribution 4.0 license
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    Using measurements of atmospheric 14CO in a global network to improve understanding of OH spatial and temporal variability
    (American Geophysical Union (AGU), 2022-12-16) Petrenko, VV; Crosier, EM; Smith, AM; Yang, B; Scholer, M; McCrea, K; Murray, LT; Colton, A; Thomas, B; Talamoa, G; Musick, R; Schaefer, H; Moss, RC; Spain, G; Yann, H; Hernandez, P; Blades, E; Chewitt-Lucas, RM; Kazemi, R; Stock, MP
    The primary source of 14C-containing carbon monoxide (14CO) in the atmosphere is via 14C production from 14N by secondary cosmic rays, and the primary sink is removal by hydroxyl radicals (OH). Variations in the abundance of 14CO that are not explained by variations in 14CO production or transport are mainly driven by variations in the abundance of OH. Because of its relatively short atmospheric lifetime (≈2 months on average), 14CO abundance is sensitive to spatial and seasonal OH variability. 14CO measurements in a new global network were made for one calendar year in 2021. Simulations in the GEOS-Chem chemical transport model (CTM) indicate that our 14CO network has good sensitivity to variations in both regional and global OH. In this presentation, we will show the new measurements as well as the CTM results available to-date.