the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 02 Apr 2026
Atmospheric Simulation Chambers in the ACTRIS Research Infrastructure
Abstract. Atmospheric simulation chambers are one of the best available tools to study atmospheric processes, as they enable experiments under conditions that are both reproducible and well-controlled. 14 unique simulation chamber facilities are part of the distributed pan-European Aerosol, Clouds and Trace Gases Research Infrastructure (ACTRIS). Their research focuses on fundamental gas-phase reaction kinetics, complex reaction mechanisms, aerosol formation and cloud chemistry, as well as other aspects of atmospheric processes. They use both simplified and complex air mixtures in their research. Results of chamber experiments enable the discovery of unknown chemical mechanisms and the determination of physicochemical parameters of atmospheric constituents. Simulation chambers are ideal for testing instruments and quality assurance of their data. The variability of their research capability is reflected in differences in the size (ranging from approximately 1 to 270 m3, the wall material, and the type of instrumentation used to measure physical parameters, gas-phase species, physicochemical properties of aerosol particles as well as cloud droplets and ice crystals. Most chambers in ACTRIS are indoors and use artificial light sources to initiate photochemical reactions while some chambers are located outside so that natural sunlight can be used. During experiments, steady state conditions may be achieved, the evolution of initial conditions may be observed, or expansion and mixing techniques may induce cloud formation. In this paper, the ACTRIS simulation chambers are described along with the quality control measures for carrying out experiments and reporting data. An overview of how users from the research community and industry can gain access to the ACTRIS simulation chambers and associated data centre is presented. Recent developments in the application of ACTRIS simulation chambers for answering current and future atmospheric research questions are discussed.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Measurement Techniques.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-1612', Anonymous Referee #1, 21 Apr 2026
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RC2: 'Comment on egusphere-2026-1612', Anonymous Referee #2, 28 Apr 2026
This manuscript presents a comprehensive overview of the atmospheric simulation chambers that are part of, or closely linked to, the ACTRIS research infrastructure. The paper covers the scientific motivations for chamber studies, the diversity of chamber designs and operating modes, available instrumentation, quality assurance procedures, and the research, training, and innovation opportunities offered to users. This is a valuable contribution and will likely become a useful reference for both new users and experienced chamber scientists. I support publication after minor revision, mainly to improve its usability for readers.
- The manuscript would be strengthened by adding one or two synthesis tables or summary figures comparing the chambers across a common set of dimensions, such as volume, material, temperature range, pressure capability, irradiation type, main scientific focus, key instrumentation, and unique capabilities.
- It would be helpful to provide a more explicit and concise summary of the user access process, including what types of access are available, how proposals are reviewed, what data obligations apply, and how users can combine chamber access with ACTRIS data-centre services or topical centres.
- The QA/QC section is important, but a concise checklist or tiered framework would make it more actionable, especially for external users who may not already be familiar with ACTRIS terminology and procedures.
- One of the strengths of ACTRIS is the diversity of its chamber facilities, but this diversity also means that experimental outcomes may not always be directly comparable because of differences in wall materials, chamber size, irradiation, mixing, cleanliness, replenishment flow, and instrumentation. The manuscript already alludes to chamber effects and characterization needs, but it would benefit from a more explicit discussion of what types of intercomparison are realistic across facilities, what limitations remain, and how ACTRIS intends to harmonize reporting without losing facility-specific strengths. This would be particularly useful for readers who might otherwise interpret the infrastructure as more standardized than it actually is.
- Figure 1 is visually appealing, but it is somewhat crowded and could be simplified for better readability.
- The terminology around “ACTRIS National Facilities,” “facilities closely connected with ACTRIS,” and chambers located in countries not yet in ACTRIS ERIC member states should be clarified and used consistently throughout the manuscript.
- Some readers would benefit from a short concluding subsection summarizing future priorities for ACTRIS chamber science, for example harmonized protocols, cross-facility intercomparison, emerging analytical needs, or links to health and climate applications.
Citation: https://doi.org/10.5194/egusphere-2026-1612-RC2 -
RC3: 'Comment on egusphere-2026-1612', Anonymous Referee #3, 05 May 2026
This paper provides a nice summary of the 14 simulation chamber facilities that comprise ACTRIS infrastructure. A comparison of the chambers highlighting the unique aspects and applications for each is definitely a worthwhile contribution to the community; however, I fail to see what new value is added in this paper that was not already covered in Laj et al 2024, the previous ACTRIS paper, which is referenced in this manuscript (DOI:https://doi.org/10.1175/BAMS-D-23-0064.1). Overall I think this manuscript is overly detailed and could introduce a little more comparison across the chambers to highlight the significance of differences in chambers and explain the rationale behind operating chambers in certain ways. My main comments are as follows:
1. Figure 1 is a bit messy. Do we really need images of each chamber? Maybe coloring by the main focus(es) for each chamber (e.g. gas-phase kinetics, aerosols, clouds, other) would be more useful. Also the grey shading is too light.
2. The most useful section to me was 2.1 which summarizes typical chamber instrumentation, as well as the Table 1 (which seems like an expansion of Table 1 from Laj et al 2024. The sections detailing each of the individual chambers are way too detailed and are often overly repetitive. It seems like a lot of extraneous information could be cut for conciseness. Also, including a list of typical instrumentation in section 2.1 and only mentioning unique instruments in the individual sections would better highlight differences between chambers.
3. Another section with typical chamber aspects / modes of operation would be helpful. Details like the source for clean air, procedures for cleaning, or how they humidify a chamber could be outlined once rather than stated in almost every single chamber section - this would help reduce the repetition. It could also help with some synthesis across the chambers, maybe by including some discussion on trade-offs of certain choices like chamber material - why do some use teflon and others use metal or quartz? Is one better for certain applications? Addressing these questions would better demonstrate the importance of some of these differences in chamber design rather than just laundry listing values / aspects for each chamber.
4. Consistency is lacking in some of the details. For example, you include wavelength of the lights for some chambers but not for others. Or you include a humidity range for some chambers and just say that others can be humidified. If you are going to include details like that, then include the same for all.
5. Some acronyms are not defined, for example, HEPA, FEP and PTFE. Please define these.
6. Later sections also seem to include a large amount of unnecessary information. For example, the reactions for jNO2 in section 4.2 could be removed. You already mention actinometry. Including one reference for this should be sufficient instead of explaining all of it in detail.
7. Also in section 4.2, the phrase "memory effects" sticks out to me. I would either define what you mean or use a different phrase that is more clear.
8. Section 6.4, please include a reference for your second listed example on the hydrogen economy
9. Section 6.5 seems unnecessary
Citation: https://doi.org/10.5194/egusphere-2026-1612-RC3
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This manuscript presents a comprehensive overview of atmospheric simulation chambers within the ACTRIS research infrastructure, including their technical characteristics, instrumentation, quality assurance procedures, and application areas. The topic is timely and highly relevant, as simulation chambers play a crucial role in advancing gas-phase chemistry, secondary organic aerosol (SOA) formation, and multiphase processes.
The manuscript is generally well organized and compiles detailed information on a wide range of chamber facilities across Europe. However, in its current form, the manuscript is overly descriptive and still lacks sufficient cross-platform synthesis, clear identification of key scientific questions, and a comprehensive summary of its major scientific contributions.
Specific Comments:
1. In the Introduction section, the authors list a large number of previous studies to illustrate the contributions of simulation chambers to atmospheric science, including structure–activity relationships, MCM/GECKO-A, HOMs, VBS, and mineral dust optical properties. However, this part mainly presents a compilation of references without sufficient synthesis. It remains unclear how these studies collectively advance mechanistic understanding, model development, or the interpretation of atmospheric observations. Further clarification and integration are needed.
2. The manuscript describes numerous applications, but the connection between specific chamber features (e.g., size, light source, material) and their suitability for particular research topics is not clearly articulated. Please clarify how different chamber designs enable different types of studies.
3. Given the importance of simulation chamber data for atmospheric modeling, could the authors clarify how ACTRIS chamber data are currently integrated into chemical transport models or mechanism development?
4. The current manuscript provides insufficient discussion of the inherent limitations of simulation chamber studies. In particular, key issues such as wall losses of both gas-phase species and particles, the use of precursor concentrations that deviate from real atmospheric levels, discrepancies between artificial light sources and natural solar radiation, and differences in chemical timescales compared to ambient atmospheric conditions should be addressed more thoroughly.
5. The manuscript would benefit from additional figures or schematics, such as classification diagrams or conceptual workflows, to better illustrate the diversity of chamber systems.