The Atmospherically Relevant Chemistry and Aerosol Box Model (ARCA) is used for simulating atmospheric chemistry, the formation of stable molecular clusters and the time evolution of aerosol particles.

The model can be used, for example, to describe the concentrations of atmospheric trace gases formed from some predefined precursors, for simulation and design of smog chamber experiments or indoor air quality estimation. The backbone of ARCAs chemical library comes from the Master Chemical Mechanism (MCM), extended with the Peroxy Radical Autoxidation Mechanism (PRAM). The chemistry scheme is further extendable with any new reactions. Molecular clustering is simulated with the Atmospheric Cluster Dynamics Code (ACDC). The particle size distribution is represented with two alternative methods whose size and grid density are fully configurable. The evolution of the particle size distribution due to the condensation of low volatile organic vapours and the Brownian coagulation is simulated using established kinetic and thermodynamic theories. Further, an optional precision optimizer ensures that all calculations are within a predifend range, taking care that no important changes are missed by too large integration time steps or computational time is wasted.

ARCA's user interface differs considerably from the previous comparable models. The model has a graphical user interface which improves its usability and the repeatability of the simulations. We hope it increases the potential of ARCA being used also outside the modelling community, for example in the experimental atmospheric sciences or by authorities.

ARCA is a freely available computational code which can be downloaded after registration, and is licenced under GNU GPL. If you are interested in applying the model, please watch the short "ARCA introduction" video. In case you have any question concerning the model, feel free to contact us under

Important! After 20 years of experience in atmospheric modelling we know that no model is perfect or completely free of any bugs. However, ARCA will be continuously further developed. To improve the model, we appreciate your feedbacks on all issues including missing chemical or physical options or simulation tasks where the model shows problems. We are aware that certain processes are still missing like e.g. a particle phase chemistry module but we have it on our agenda and are eager to get your feedbacks what other processes should be considered in the near future.

ARCA introduction video

This video will tell you why and how ARCA was constucted and how you will recieve the model. So, please watch this 8 minutes video before you proceed.



Please press here and you will be guided to the registration website of ARCA. There are only certain basic information required and you will get a confirmation email after the registration is completed. 

Important! If you have more people in your group who apply the ARCA box model please tell everyone to register. In this case they will get a notification from the ARCA-team if a new version of the model is available and they will be invited to virtual or local ARCA-workshops.

ARCA manual and tutorials

Please press here and you will be directed to the online user manual for the Atmospherically Relevant Chemistry and Aerosol box model. The manual will tell you how to install ARCA on different operating systems, the structure and how to use the graphical user interface. There are several tutorials in the manual which will assist you to have a smooth and easy start with the new model ARCA.

ARCA publications

The list below includes all ARCA publications and group members are highlighted in bold in the author list. Clusius et al. 2022 presents the general description of ARCA and should be used as the main reference publication. 


  • Clusius, P., Xavier, C., Pichelstorfer, L., Zhou, P., Olenius, T., Roldin, P., and Boy, M.: Atmospherically Relevant Chemistry and Aerosol box model – ARCA box (version 1.2), Geosci. Model Dev., 15, 7257–7286,, 2022
  • Hulkkonen, M., R. O. Kaaronen, Kokkola, H., Mielonen, T., Clusius, P., Xavier, C., Hellen, H., Niemi, J. V., Malila, J.: Modeling non-linear changes in an urban setting: From pro- environmental affordances to responses in behavior, emissions and air quality. Ambio,, 2023.
  • Saarikoski, S., Hellén, H., Praplan, A. P., Schallhart, S., Clusius, P., Niemi, J. V., Kousa, A., Tykkä, T., Kouznetsov, R., Aurela, M., Salo, L., Rönkkö, T., Barreira, L. M. F., Pirjola, L., and Timonen, H.: Characterization of volatile organic compounds and submicron organic aerosol in a traffic environment, Atmos. Chem. Phys., 23, 2963–2982,, 2023.
  • Shang, D., Hu, M., Wang, X., Tang, L., Clusius, P. S., Qiu, Y., Yu, X., Chen, Z., Zhang, Z., Dao, X., Zeng, L., Guo, S., Wu, Z., and Boy, M.: Spatial Inhomogeneity of New Particle Formation in Urban and Mountainous Atmospheres of the North China Plain during the 2022 Winter Olympics, Atmosphere, 14(9), 1395,, 2023