the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Nov 2025
Evaluating the EPICC-Model for Regional Air Quality Simulation: A Comparative Study with CAMx and CMAQ
Abstract. This study presents a systematic evaluation of China’s independently developed the EPICC-Model for regional PM2.5 and MDA8 O3 simulations against established international models, using unified WRF meteorological fields and a multi-source integrated emission inventory. Results highlight the strengths of the EPICC-Model in several aspects: it achieves relatively high spatial consistency for PM2.5, with an annual index of agreement (IOA) of 0.80, and accurately captures pollution patterns in heavily polluted North China. It also demonstrates improved performance in simulating summer O3 peaks, reducing maximum biases by more than 20 μg m-3, primarily through enhanced heterogeneous HONO formation and nitrate photolysis pathways that elevate OH concentrations, and it incorporates the CB6r5 mechanism to better represent biogenic VOC oxidation. The model exhibits the highest hit rate (45.6 %) for identifying moderate PM2.5 and moderate O3 pollution events and successfully reproduces persistent compound pollution episodes. However, all models share common limitations, including insufficient capability in reproducing heavy pollution episodes, systematic underestimation of SO42-, and uncertainties in SOA-related OC simulations. Future improvements should focus on refining secondary aerosol chemistry, emission inventories, and boundary layer representations. This study has not only demonstrated the performance of the EPICC-Model against international benchmarks but also provides guidance for improving regional and global air quality models.
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2025-4441', Anonymous Referee #1, 14 Nov 2025
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CC1: 'Reply on RC1', Mengjie Lou, 12 Feb 2026
Dear Reviewer,
We sincerely thank you for your constructive comments. We have prepared point-by-point responses to all your suggestions, which will be uploaded together after receiving feedback from the other reviewers. Here, we first address the main issues you raised.
Regarding Comment 1 on the settings of the three models (EPICC-Model, CAMx, and CMAQ), our responses are as follows:
A) Vertical Layer Structure:
The primary reason for differences in vertical layer structures among the three models is that the EPICC-Model adopts a terrain-following height coordinate, while CAMx and CMAQ employ terrain-following sigma-pressure coordinates. Due to these differences in vertical coordinate definitions and internal numerical implementations, it is not feasible to maintain a completely identical vertical layer structure across all three models.In terms of the transmission of WRF meteorological fields, this study used WRF v3 as the meteorological driver. WRF v3 uses a terrain-following sigma-pressure coordinate system. The meteorological fields were processed using MCIP v4, which supports vertical layer reduction of WRF outputs. Note that WRF v4 introduced a hybrid vertical coordinate system, and vertical layer reduction is generally not recommended in newer versions; consequently, newer MCIP versions no longer support this operation.
Regarding boundary conditions, the term “default” in the manuscript refers to the built-in profile-type boundary condition schemes in both models. These schemes construct vertical concentration profiles based on average background concentrations and generate lateral boundary concentrations through interpolation. The corresponding configuration parameters are available in the model setup files.
B) Chemical Mechanism Choice:
Although CB6 is a more recent update compared to CB05, there is currently no consistent evidence that CB6 performs better than CB05 over China. CB05 has been widely applied in long-term regional air quality simulations in China and has undergone extensive evaluation, demonstrating good stability and applicability. Therefore, CB05 was retained in this study.For the MEIC emission inventory, temporal allocation factors were applied to distribute emissions at monthly, daily, and hourly scales, followed by spatial allocation using a first-order conservative interpolation method. Chemical speciation was conducted with reference to the SPECIATE database (https://www.epa.gov/air-emissions-modeling/speciate), and species mapping was performed separately according to the chemical mechanism used in each model to ensure mass conservation within each mechanism framework. Therefore, no VOC mass was lost due to incompatibility between CB6 species and CB05.
C) Model Processes:
Regarding the vertical advection scheme, we confirm that CAMx v7.0 was used in this study, and the PPM option can indeed be enabled. For vertical diffusion, CAMx applies a first-order K-theory framework to calculate vertical diffusion fluxes, with vertical diffusivity coefficients derived diagnostically from WRF meteorological fields following the YSU boundary layer parameterization approach. Thus, the YSU-related description has been retained.For secondary organic aerosol treatment, the updated SOAP2.2 scheme was used rather than the original SOAP scheme, and this has been revised in both the main text and Table 1.
For photolysis processes, CAMx first uses the full-science TUV model as a preprocessor to generate photolysis rate input files, and then applies a streamlined TUV module within the model to dynamically adjust photolysis rates according to cloud and aerosol conditions. The EPICC-Model adopts the same approach. To avoid ambiguity, both the full-science TUV and streamlined TUV components have been explicitly listed in Table 1.
We hope these clarifications adequately address your concerns.
Sincerely,
Mengjie Lou
Beijing Normal UniversityCitation: https://doi.org/10.5194/egusphere-2025-4441-CC1
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CC1: 'Reply on RC1', Mengjie Lou, 12 Feb 2026
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CEC1: 'Comment on egusphere-2025-4441 - No compliance with the policy of the journal', Juan Antonio Añel, 07 Dec 2025
Dear authors,
Unfortunately, after checking your manuscript, it has come to our attention that it does not comply with our "Code and Data Policy".
https://www.geoscientific-model-development.net/policies/code_and_data_policy.htmlYou have archived your the code and data used in your work (with the exception of one Zenodo repository) in sites that do not comply with our policy and requirements. Therefore, the current situation with your manuscript is irregular. Please, publish your code in one of the appropriate repositories and reply to this comment with the relevant information (link and a permanent identifier for it (e.g. DOI)) as soon as possible, as we can not accept manuscripts in Discussions that do not comply with our policy. Also, please include the relevant primary input/output data.
In your reply to this comment, please, include a new version of the "Code and Data Availability" section of your manuscript that addresses and solve all the mentioned issues.
I must note that if you do not fix this problem, we cannot continue with the peer-review process or accept your manuscript for publication in our journal.
Juan A. Añel
Geosci. Model Dev. Executive EditorCitation: https://doi.org/10.5194/egusphere-2025-4441-CEC1 -
AC1: 'Reply on CEC1', Qizhong Wu, 27 Jan 2026
Dear Prof. Juan A. Añel
My name is Qizhong Wu, from Beijing Normal University, one of the corresponding authors on the manuscript "egusphere-2025-2918" and "egusphere-2025-4441". To support the peer review of the submissions in accordance with the GMD code and data policy, the EPICC-Model Working Group has provided the access to the EPICC-Model source code via the Zenodo link as described in the email, which has sent to you and editor@mailarchive.copernicus.org.Regards,Qizhong WuBeijing Normal UniversityCitation: https://doi.org/10.5194/egusphere-2025-4441-AC1 -
CEC2: 'Reply on AC1 - No compliance with the policy of the journal', Juan Antonio Añel, 12 Feb 2026
Dear authors,
We have noted that you continue making actions on the peer-review process for this manuscript, which we have communicated you days ago that is stopped until you solve the pending issues regarding compliance with the Code and Data policy of the journal.
To be sure that you are aware of them, I am pasting below the communication by email that we sent you after consultation by such way of communication. Please, refrain from replying to reviewers or taking any other action on your manuscript until we have communicated you that the issues related to the code and data in your manuscript are solved.
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We have reviewed your submission of your manuscript entitled "Evaluating the EPICC-Model for Regional Air Quality Simulation: A Comparative Study with CAMx and CMAQ"
Unfortunately, as it is right now, we can not accept it to continue the review process or publication in our journal.
You have submitted with your review the EPICC model code using a private repository. However, its licence, included in the repository, clearly establishes that the model can be redistributed. Therefore, you must publish the model in an open repository.
However, during the review of the EPICC code, we have discovered that right now the model is illegal regarding its use and redistribution, and therefore, we can not publish a model that violates the current copyright law.
Namely, we have detected that at least several routines (e.g, SOAP.F90, wrf_micromet.F90) violate the license of the software on which they are based (CAMx v7.0) --actually, they look like a literal copy--. The license for CAMx v7.0 requests to preserve the notice on the role of their developers, "Ramboll US Corporation", on any software developed based on it, and you do not do it in the license of the EPICC model. Another routine, "convect43c.f", is a literal copy of one by Kerry Emanuel, and there is no evidence that it has a license that allows its use or redistribution.
Therefore, we can not continue considering your manuscript for review or publication in Geosci. Model Dev. until you have solved the pending legal and redistribution issues with the EPICC model, and provided a version of your code that complies with the existing copyright laws. Also, then you will need to share the code openly and provide a new "Code and Data Availability" section that complies with the requirements of the journal.
Please, let us know about your intentions regarding your manuscript, if you intend to solve the mentioned issues and submit a new version that complies with the law and the policy of the journal, or if you are withdrawing your manuscript.Juan A. Añel
Geosci. Model Dev. Executive Editor
Citation: https://doi.org/10.5194/egusphere-2025-4441-CEC2
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CEC2: 'Reply on AC1 - No compliance with the policy of the journal', Juan Antonio Añel, 12 Feb 2026
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AC1: 'Reply on CEC1', Qizhong Wu, 27 Jan 2026
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Publisher’s note: a supplement was added to this comment on 11 December 2025.
Please see my review in the attached file.