Advective transport is done using the highly accurate and low-diffusive Second Order Moments (SOM) scheme (Prather et al., 2008), with the polar cap update described by Søvde et al (2012). The parameterization of deep convection is based on the Tiedke mass flux scheme (Tiedke, 1989), while boundary layer mixing is treated according to the Holtslag K-profile scheme (Holtslag et al., 1990). Transport is driven by the precalculated meteorological data.
Wet scavenging, i.e. removal of atmospheric constituents by precipitation, is an important process in the atmosphere. The OsloCTM3 treats large-scale and convective scavenging separately (Søvde et al. 2012; Lund et al. 2018). While the convective scavenging is similar to OsloCTM2 (Berglen et al., 2004), CTM3 use a more detailed treatment of large-scale scavenging (Neu and Prather, 2012). The latter is a cloud model, using meteorological variables from the model input to calculate how chemical components or aerosols are taken up by large-scale rain or ice, how much evaporates, and finally how much is removed at the surface.
Dry scavenging, or dry deposition, is the removal of atmospheric constituents by gravitational settling or by uptake at the surface. Gravitational settling may be important for large particles, but for gases this is not a removal process at the surface. Surface uptake can be either sticking at the surface (on water or soil or vegetation) or uptake by plants. The default dry deposition scheme uses dry deposition velocities from Wesely (1989), with a distinction between land cover types and day/night and summer/winter. This applies for gases; aerosols have their own deposition velocities.
Recently, work was undertaken to implement a new dry deposition scheme in the model for selected gaseous species, including ozone (Falk & Søvde Haslerud, 2019). This new scheme, based on Simpson et al. (2012), takes into account the state of atmosphere and boundary layer dynamics, and is hence a physically more detailed treatment. Globally, a significantly lower annual total ozone deposition was estimated with the new scheme compared to the original.
Falk, S. and Søvde Haslerud, A.: Update and evaluation of the ozone dry deposition in Oslo CTM3 v1.0, Geosci. Model Dev., 12, 4705–4728, https://doi.org/10.5194/gmd-12-4705-2019, 2019.
Holtslag, A. A. M.; E. I. F. DeBruijn, and H.-L. Pan: A High resolution air mass transformation model for short-range weather forecasting, Mon. Weather Rev., vol. 118, pp. 1561-1575, doi:10.1175/1520-0493(1990)118<1561:AHRAMT>2.0.CO;2, 1990.
Lund, M. T., Myhre, G., Haslerud, A. S., Skeie, R. B., Griesfeller, J., Platt, S. M., Kumar, R., Myhre, C. L., and Schulz, M.: Concentrations and radiative forcing of anthropogenic aerosols from 1750 to 2014 simulated with the Oslo CTM3 and CEDS emission inventory, Geosci. Model Dev., 11, 4909–4931, https://doi.org/10.5194/gmd-11-4909-2018, 2018.
Prather, Michael J.; Xin Zhu, Susan E. Strahan, Stephen D. Steenrod, and Jose M. Rodriguez: Quantifying errors in trace species transport modeling, Proc. Natl. Acad. Sci., 105(50), 19617-19621, doi:10.1073/pnas.0806541106, 2008.
Simpson, D.; A. Benedictow, H. Berge, R. Bergström, L. D. Emberson, H. Fagerli, C. R. Flechard, G. D. Hayman, M. Gauss, J. E. Jonson, M. E. Jenkin, A. Nyíri, C. Richter, V. S. Semeena, S. Tsyro, J.-P. Tuovinen, Á. Valdebenito, and P. Wind: The EMEP MSC-W chemical transport model - technical description, Atmos. Chem. Phys., 12, 7825-7865, doi:10.5194/acp-12-7825-2012, 2012.
Søvde, O. A.; M. J. Prather, I. S. A. Isaksen, T. K. Berntsen, F. Stordal, X. Zhu, C. D. Holmes and J. Hsu: The chemical transport model Oslo CTM3, Geosci. Model Dev., 5, 1441-1469, doi:10.5194/gmd-5-1441-2012, 2012.
Tiedke, M: A Comprehensive Mass Flux Scheme for Cumulus Parameterisation on Large Scale Models, Mon. Weather Rev., vol. 117, pp. 1779-1800, doi:10.1175/1520-0493(1989)117<1779:ACMFSF>2.0.CO;2, 1990.
Wesely, M. L: Parameterization of surface resistances to gaseous dry deposition in regional-scale numerical models, Atm. Env., Vol. 23, Issue 6, 1293-1304, doi:10.1016/0004-6981(89)90153-4, 1989