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https://doi.org/10.5194/egusphere-2025-3057
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/egusphere-2025-3057
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
10 Sep 2025
| 10 Sep 2025
Status: this preprint is open for discussion and under review for Geoscientific Model Development (GMD).
Introducing Volatile Organic Compound Model Intercomparison Project (VOCMIP)
Abstract. Volatile organic compounds (VOCs) play an important role in atmospheric chemistry, influencing the cycling of peroxy and hydroxyl radicals, the formation of tropospheric ozone, hydrogen, secondary organic aerosol, and the lifetime of methane and other greenhouse gases. Their interactions shape overall atmospheric composition and air quality, with implications for both climate and human health. Given their significance, accurate representation of VOCs in global atmospheric chemistry models is crucial. In this context, we introduce the Volatile Organic Compound Model Intercomparison Project (VOCMIP) and invite atmospheric chemistry modelling groups to participate in this collaborative effort. VOCMIP aims to identify model consistencies and discrepancies, enhance the formulation of chemical mechanisms, and advance our understanding of VOC-related processes in the atmosphere. Global atmospheric chemistry model output will be compared to in situ measurements from surface stations and aircraft campaigns, plus satellite data for key VOCs. Special emphasis will be placed on formaldehyde (HCHO), examining its chemical sources and sinks given its central role as a radical source and as an intermediate in the photochemical destruction of VOCs.
How to cite. Myhre, G., Hodnebrog, Ø., Krishnan, S., Sand, M., Sandstad, M., Skeie, R. B., Clarisse, L., Franco, B., Millet, D. B., Wells, K. C., Archibald, A., Bryant, H. N., Chaudhri, A. T., Stevenson, D. S., Hauglustaine, D., Prather, M., Kaiser, J. C., Olivie, D. J. L., Schulz, M., Wild, O., Wang, Y., Salameh, T., Williams, J. E., Le Sager, P., Paulot, F., Tsigaridis, K., and Plaas, H. E.: Introducing Volatile Organic Compound Model Intercomparison Project (VOCMIP), EGUsphere [preprint], https://doi.org/10.5194/egusphere-2025-3057, 2025.
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CICERO Center for International Climate Research, 0318 Oslo, Norway
Øivind Hodnebrog
CICERO Center for International Climate Research, 0318 Oslo, Norway
Srinath Krishnan
CICERO Center for International Climate Research, 0318 Oslo, Norway
Maria Sand
CICERO Center for International Climate Research, 0318 Oslo, Norway
Marit Sandstad
CICERO Center for International Climate Research, 0318 Oslo, Norway
Ragnhild B. Skeie
CICERO Center for International Climate Research, 0318 Oslo, Norway
Lieven Clarisse
Spectroscopy, Quantum Chemistry and Atmospheric Remote Sensing (SQUARES), BLU‐ULB Research Centre, Université Libre de Bruxelles (ULB), 1050 Brussels, Belgium
Bruno Franco
Spectroscopy, Quantum Chemistry and Atmospheric Remote Sensing (SQUARES), BLU‐ULB Research Centre, Université Libre de Bruxelles (ULB), 1050 Brussels, Belgium
Dylan B. Millet
University of Minnesota, St. Paul, MN, 55108, USA
Kelley C. Wells
University of Minnesota, St. Paul, MN, 55108, USA
Alexander Archibald
Yusuf Hamied Department of Chemistry, University of Cambridge, UK
National Centre for Atmospheric Science, UK
Hannah N. Bryant
School of GeoSciences, The University of Edinburgh, EH9 3FF, UK
Alex T. Chaudhri
School of GeoSciences, The University of Edinburgh, EH9 3FF, UK
David S. Stevenson
School of GeoSciences, The University of Edinburgh, EH9 3FF, UK
Didier Hauglustaine
Laboratoire des Sciences du Climat et de l’Environnement (LSCE), CEA/CNRS/UVSQ, IPSL, Université Paris-Saclay, Gif-sur-Yvette, France
Michael Prather
Earth System Science Department, University of California Irvine, Irvine, CA, USA
J. Christopher Kaiser
Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
Dirk J. L. Olivie
Norwegian Meteorological Institute, Oslo, Norway
Michael Schulz
Norwegian Meteorological Institute, Oslo, Norway
Oliver Wild
Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK
Ye Wang
Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK
Thérèse Salameh
IMT Nord Europe, Institut Mines-Télécom, Univ. Lille, Centre for Energy and Environment, F-59000, Lille -France
Jason E. Williams
R&D Weather and Climate Modeling, Royal Netherlands Meteorological Institute, De Bilt, the Netherlands
Philippe Le Sager
R&D Weather and Climate Modeling, Royal Netherlands Meteorological Institute, De Bilt, the Netherlands
Fabien Paulot
NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ, USA
Kostas Tsigaridis
Center for Climate Systems Research, Columbia University, New York, NY, USA
NASA Goddard Institute for Space Studies, New York, NY, USA
Haley E. Plaas
Center for Climate Systems Research, Columbia University, New York, NY, USA
NASA Goddard Institute for Space Studies, New York, NY, USA
Short summary
Volatile organic compounds (VOCs) affect air quality and climate, but their behavior in the atmosphere is still uncertain. We launched a global research effort to compare how different models represent these compounds and to improve their accuracy. By analyzing model results alongside observations and satellite data, we aim to better understand the atmospheric composition of these compounds.
Volatile organic compounds (VOCs) affect air quality and climate, but their behavior in the...
The manuscript egusphere-2025-3057 introduces a new model intercomparison project, named VOCMIP. After providing a comprehensive introduction and clear motivation, the authors describe the experimental design and the observational data used in the study. While I believe this is an excellent initiative and fully support the planned work, I must admit that I have mixed feelings about the manuscript itself.
I began reading the manuscript with great enthusiasm and found the introduction to be a well-crafted and engaging overview. Unfortunately, the experimental design does not live up to the same standard, and, more importantly, the manuscript lacks a clear scientific focus for the project. While some aspects of this focus are touched upon in the introduction, they are never fully articulated or clearly defined.
Hence, although the concept is promising, the manuscript lacks certain essential details and a clear scientific plan that are necessary for a more robust understanding and evaluation of the project. I therefore recommend that the authors revisit the scientific goals of the project and provide a more detailed and precise description of how the intercomparison project will address these goals.
General comments:
As I mentioned earlier, I am unclear about the primary focus of this model intercomparison project. At the moment, it appears to center on "checking the differences in concentrations against observations," but the specific scientific goals are not clearly articulated. It would be very helpful to have these goals explicitly outlined.
If the primary aim is to investigate the chemical mechanisms, why not start by using box models to isolate the chemical processes from the noise introduced by varying atmospheric forcings? For certain models listed (e.g., EC-Earth, EMAC), different chemical decomposition schemes are available. Why not compare the results from the same model but using different decomposition schemes? This could simplify the analysis and help in pinpointing the sources of variability.
If the goal is to study the lifetime of VOCs within each chemical mechanism, why not use the same OH field across models? Since the models are capable of forcing methane at the surface (as mentioned in line 115), they should also be able to apply a consistent oxidative power across the atmosphere.
Alternatively, if the primary objective is to investigate the different parameterizations of deposition, why not focus on intercomparisons of the deposition algorithms? If photolysis rates are the main area of interest, then why not perform an intercomparison of those as well?
While it is certainly possible to pursue all of these objectives, each would require separate simulations. A thorough and meaningful comparison would necessitate a well-thought-out experimental design to ensure the results are attributable to specific causes. Otherwise, we risk obtaining a range of results without understanding the underlying reasons for the differences.
I am concerned that this exercise might turn into a "race" to see which model best matches observations. While this is undoubtedly valuable, I believe there is a greater opportunity here: to understand why the best-performing models are successful. This deeper insight could yield more valuable scientific knowledge.
Specific comments:
*) line 42 : I would appreciate a clear definition of VOCs : when is an organic compound volatile?
*) lines 45-47 : I would move the descriptions of different compounds forming VOCs just after the definition (at the beginning of the text).
*) line 77 : Would be great to add a references on this statement (i.e. nucleation of VOCs' oxidation products)
*) line 82 : "Despite" sounds odd to me in this sentence
*) line 94 : If I understood correctly, emissions are possible by conserving mass, carbon, moles or also reactivity, as described in detail few lines before.
*) line 98 : I would remove the reference to the VOCMIP, as this has not yet introduced (coming later in line 110)
*) line 114 : I found quite funny that you describe methane as "the most aboundant VOC in the atmosphere and the dominant source of key VOCs" , but you will neglect it in this work. I also do not really understand the connection with methane being prescribed at the surface. Actually, this would be even an advantage, as most of the dynamical-driven processes are forced and you could simply focus on the chemistry of methane. In addition, while not a major focus, it seems (table 1 and 2) that you will need exactly the same data of all the other components. So there is no real differences from the technical point of view between methane and other VOCs.
*) Line 132 : What is the motivation to select these emissions? What about different speiciation methods in the emissions? How do you assure that the same amount of VOCs (either in reactivity or mass) are actually emitted ?
*) Line 133 : "supplemented with natural emissions" is quite vague: if you have completely different emissions you cannot expect any intercomparison at all (or only partially).
*) Table 2: What is the definition of "Chemical destruction"? The total chemical sink (including photolysis)? Would be a speciation (e.g. OH oxidation or NO3 oxidation) be more informative?
*) Line 192 : Some of these acronyms were not introduced before (and some only in the Fig.2 label). Would be very interesting if you have a stragety to compare models with "BIGALK" with models that have a more (or less) chemical detail (i.e. VOCs speciation).
*) Line 195 : "within carious project" sounds a bit vague.