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Published January 16, 2020 | Supplemental Material + Published
Journal Article Open

Exploring Oxidation in the Remote Free Troposphere: Insights from Atmospheric Tomography (ATom)

Abstract

Earth's atmosphere oxidizes the greenhouse gas methane and other gases, thus determining their lifetimes and oxidation products. Much of this oxidation occurs in the remote, relatively clean free troposphere above the planetary boundary layer, where the oxidation chemistry is thought to be much simpler and better understood than it is in urban regions or forests. The NASA airborne Atmospheric Tomography study (ATom) was designed to produce cross sections of the detailed atmospheric composition in the remote atmosphere over the Pacific and Atlantic Oceans during four seasons. As part of the extensive ATom data set, measurements of the atmosphere's primary oxidant, hydroxyl (OH), and hydroperoxyl (HO₂) are compared to a photochemical box model to test the oxidation chemistry. Generally, observed and modeled median OH and HO₂ agree to with combined uncertainties at the 2σ confidence level, which is ~±40%. For some seasons, this agreement is within ~±20% below 6 km altitude. While this test finds no significant differences, OH observations increasingly exceeded modeled values at altitudes above 8 km, becoming ~35% greater, which is near the combined uncertainties. Measurement uncertainty and possible unknown measurement errors complicate tests for unknown chemistry or incorrect reaction rate coefficients that would substantially affect the OH and HO₂ abundances. Future analysis of detailed comparisons may yield additional discrepancies that are masked in the median values.

Additional Information

© 2019 The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Received 17 SEP 2019; Accepted 19 DEC 2019; Accepted article online 27 DEC 2019. The authors thank the NASA ATom management team, pilots, logistical support team, aircraft operations team, and fellow scientists. Data and Model Availability: The data and model used in this paper are publicly available: data: https://doi.org/10.3334/ORNLDAAC/1581; model framework: https://sites.google.com/site/wolfegm/models; MCMv331 chemical mechanism: http://mcm.leeds.ac.uk/MCM/. Author Contribution: DOM, WHB, and ABT made the OH and HO2 measurements, performed the model runs, analyzed the data, and wrote the initial draft of the manuscript. GMW provided support the F0AM model framework. WHB, DOM, ABT, HMA, ECA. DRB, TPB, RC, JDC, BCD, GSD, JPD, JWE, SRH, TFH, RAH, EJH, RSH, MJK, KM, FLM, JMN, JAN, JP, TBR, JMS CS., APT, CT, KU, PRV, POW, GMW provided ATom measurements used for the modeling and edits for the manuscript. The authors declare no financial or affiliation conflicts-of-interest. This study was supported by the NASA grant NNX15AG59A. This material is based upon work supported by the National Center for Atmospheric Research, which is a major facility sponsored by the National Science Foundation under Cooperative Agreement No. 1852977. MJK was supported by NSF fellowship 1524860 for the first year of this study.

Attached Files

Published - Brune_et_al-2020-Journal_of_Geophysical_Research__Atmospheres.pdf

Supplemental Material - jgrd55975-sup-0001-2019jd031685-si.pdf

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Brune_et_al-2020-Journal_of_Geophysical_Research__Atmospheres.pdf
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Additional details

Created:
August 22, 2023
Modified:
October 23, 2023