Tropospheric Ozone Assessment Report II: Overview

Abstract The International Global Atmospheric Chemistry (IGAC) Tropospheric Ozone Assessment Report Phase II (TOAR-II) provides an updated, comprehensive assessment of the global distribution, burden and trends of tropospheric ozone, building on the foundation established by TOAR-I, 2014–2019. Accurate knowledge of tropospheric ozone concentrations remains essential for understanding atmospheric chemistry with far reaching implications for climate radiative forcing, vegetation damage and human health. Here, we present the process and summarize the main conclusions of TOAR-II, 2020–2026. Following TOAR-I, TOAR-II provides updates to trends in ozone concentrations and other metrics and addresses trends in ozone precursor emissions. This was accomplished as a community-driven process by forming Focus Working Groups to continue and expand on TOAR-I topics. Focus Working Group findings were published in a TOAR-II Community Special Issue with 58 review and original research papers. From this Community Special Issue, as well as other relevant literature, seven assessment papers were synthesized and submitted to this issue, along with this overview paper. These papers update the primary themes of TOAR-I: health, vegetation and climate; address unresolved uncertainties and inconsistencies in TOAR-I satellite ozone observations; provide an overdue update on stratosphere–troposphere exchange (STE) and present critical regional assessments for ozone over oceanic and polar regions, and South America. The TOAR-II assessment would not be possible without an extensive data collection and data harmonization effort. TOAR-II data are curated under findable, accessible, interoperable and reusable principles, and the TOAR data repository has been certified by the Core Trust Seal. In addition, TOAR-II developed common statistical analysis guidelines for the assessment papers. Although TOAR-II provides an extensive assessment of the current state of tropospheric ozone, many gaps and scientific challenges remain for future assessments. In particular, there is under-sampling of ozone across Southeast Asia and the Southern Hemisphere, especially Africa and Australia/Oceania. Low-cost sensor data and geostationary satellite data for tropospheric ozone, which still require evaluation, should be included. Ozone produced from wildfires and exacerbated by extreme weather events, and attribution of changes in ozone to pollution regulations on precursor emissions require greater attention in future analyses. These topics will be prioritized in the IGAC TOAR-III effort along with incorporating advances in artificial intelligence (AI) and strengthening collaboration with policy-relevant initiatives. This article is part of the theme issue ‘Tropospheric Ozone Assessment Report II’.

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Journal
Philosophical Transactions of the Royal Society A Mathematical Physical and Engineering Sciences
Published
2026-10-26
DOI
https://doi.org/10.1098/rsta.2025.0275
Primary Topic
Atmospheric chemistry and aerosols
Type
article
Field-Weighted Citation Impact
0.00

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article

Tropospheric Ozone Assessment Report II: Overview

Lisa D. Emberson, James M. Keeble, Gaige Hunter Kerr, Yugo Kanaya et al.
Philosophical Transactions of the Royal Society A Mathematical Physical and Engineering Sciences
Atmospheric chemistry and aerosols
article

Tropospheric Ozone Assessment Report II: Overview

Lisa D. Emberson, James M. Keeble, Gaige Hunter Kerr, Yugo Kanaya, J. Jason West, Erika von Schneidemesser, Alfonso Saiz‐Lopez, Theodore K. Koenig, Paul Thomas Griffiths, Gabriele G. Pfister, Martin G. Schultz, Sophie Szopa, H. M. Worden, Owen R. Cooper, Kazuyuki Miyazaki, Roberto Sommariva, Daan Hubert, Keding Lu, Rodrigo Seguel, Jacek W. Kaminski, Raeesa Moolla, Bärbel Sinha
article en

Abstract

Abstract The International Global Atmospheric Chemistry (IGAC) Tropospheric Ozone Assessment Report Phase II (TOAR-II) provides an updated, comprehensive assessment of the global distribution, burden and trends of tropospheric ozone, building on the foundation established by TOAR-I, 2014–2019. Accurate knowledge of tropospheric ozone concentrations remains essential for understanding atmospheric chemistry with far reaching implications for climate radiative forcing, vegetation damage and human health. Here, we present the process and summarize the main conclusions of TOAR-II, 2020–2026. Following TOAR-I, TOAR-II provides updates to trends in ozone concentrations and other metrics and addresses trends in ozone precursor emissions. This was accomplished as a community-driven process by forming Focus Working Groups to continue and expand on TOAR-I topics. Focus Working Group findings were published in a TOAR-II Community Special Issue with 58 review and original research papers. From this Community Special Issue, as well as other relevant literature, seven assessment papers were synthesized and submitted to this issue, along with this overview paper. These papers update the primary themes of TOAR-I: health, vegetation and climate; address unresolved uncertainties and inconsistencies in TOAR-I satellite ozone observations; provide an overdue update on stratosphere–troposphere exchange (STE) and present critical regional assessments for ozone over oceanic and polar regions, and South America. The TOAR-II assessment would not be possible without an extensive data collection and data harmonization effort. TOAR-II data are curated under findable, accessible, interoperable and reusable principles, and the TOAR data repository has been certified by the Core Trust Seal. In addition, TOAR-II developed common statistical analysis guidelines for the assessment papers. Although TOAR-II provides an extensive assessment of the current state of tropospheric ozone, many gaps and scientific challenges remain for future assessments. In particular, there is under-sampling of ozone across Southeast Asia and the Southern Hemisphere, especially Africa and Australia/Oceania. Low-cost sensor data and geostationary satellite data for tropospheric ozone, which still require evaluation, should be included. Ozone produced from wildfires and exacerbated by extreme weather events, and attribution of changes in ozone to pollution regulations on precursor emissions require greater attention in future analyses. These topics will be prioritized in the IGAC TOAR-III effort along with incorporating advances in artificial intelligence (AI) and strengthening collaboration with policy-relevant initiatives. This article is part of the theme issue ‘Tropospheric Ozone Assessment Report II’.

Philosophical Transactions of the Royal Society A Mathematical Physical and Engineering SciencesVol. 384(2332)
TH Köln - University of Applied Sciences (DE), Universidad de Santiago de Chile (CL), NSF National Center for Atmospheric Research (US), University of North Carolina at Chapel Hill (US), California Institute of Technology (US), Centre National de la Recherche Scientifique (FR), Japan Agency for Marine-Earth Science and Technology (JP), Jet Propulsion Laboratory (US), Stockholm Environment Institute (GB), Consejo Superior de Investigaciones Científicas (ES), University of Leicester (GB), University of California, Los Angeles (US), Pontificia Universidad Católica de Chile (CL), Indian Institute of Science Education and Research Mohali (IN), Forschungszentrum Jülich (DE), University of Cologne (DE), University of the Witwatersrand (ZA), George Washington University (US), Université de Versailles Saint-Quentin-en-Yvelines (FR), Royal Belgian Institute for Space Aeronomy (BE), Hong Kong University of Science and Technology (HK), Peking University (CN), Commissariat à l'Énergie Atomique et aux Énergies Alternatives (FR), Université Paris-Saclay (FR), CEA Paris-Saclay - Etablissement de Saclay (FR), University of California System (US), University of Bristol (GB), Centre For Sustainable Urban Development (CL), Research Institute for Sustainability at GFZ (DE), Institut Pierre-Simon Laplace (FR), Institute of Environmental Protection (PL), Laboratoire des Sciences du Climat et de l'Environnement (FR), CEA Paris-Saclay (FR), NOAA Chemical Sciences Laboratory (US), Instituto de Química Física Blas Cabrera (ES), GFZ Helmholtz Centre for Geosciences (DE), NSF NCAR Atmospheric Chemistry Observations & Modeling (US), Jülich Supercomputing Centre (DE), University of York (GB), Lancaster University (GB), University of Birmingham (GB), University of Hong Kong (HK)
National Science Foundation, National Aeronautics and Space Administration, California Institute of Technology, Belgian Federal Science Policy Office, Jet Propulsion Laboratory
Openalex Percentile: Top 21%
Atmospheric chemistry and aerosols
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