Aerosols and Greenhouse Gases

Greenhouse gases and aerosols interact with short-wave and long-wave radiation.  The effects can heat or cool the atmosphere and surface and so can impact the forecasts.

Greenhouse gases considered are:

  • water vapour.
  • carbon dioxide.
  • ozone.
  • methane.
  • nitrous oxide.
  • four CFC compounds.

Aerosol types considered are:

  • sea salt (three different sized particles).
  • desert dust (three different sized particles).
  • organic matter.
  • black carbon.
  • ammonium sulphate.

Several of the aerosol species are hydrophilic.  This means the particles swell as relative humidity increases making the aerosol more optically thick.  If this process is activated in the model it can act to reduce visibility in humid conditions.


For reliable treatment of the interaction with radiation the global distribution of greenhouse gases and aerosols needs to be well represented .  There are two different configurations of the IFS that are used operationally, and which represent their global distribution in different ways:

  • CAMS forecasts. Air-quality forecasts for the Copernicus Atmosphere Monitoring Service (CAMS), including the CAMS reanalysis, gases and aerosols are represented by prognostic variables.  These are advected with model winds, and source and sink processes are also represented.
    • For greenhouse gases, fluxes taken into account are from:
      • anthropogenic sources.
      • vegetation.
      • wetlands.
      • oceans.
      • chemical reactions between gases.


    • For aerosols, fluxes taken into account are from:
      • anthropogenic aerosols (e.g. from urban sources and biomass burning using a database of surface sources). 
      • natural aerosols (e.g. dust raised by wind and sea salt from breaking waves - depends on forecast wind speed).
    • Aerosol particles are advected by:
      • the mean winds.
      • vertical diffusion.
      • convective lofting.
      • sedimentation.
      • dry deposition.
      • wet deposition (by large-scale and convective precipitation).


  • All other forecasts (medium range, extended-range and seasonal forecasts, and ECMWF reanalysis products).  In all non-CAMS configurations of the IFS, gases and aerosols are represented by a monthly-mean climatology.

For greenhouse gases the climatology varies with month, latitude and height, but not longitude.

For aerosol species, the climatology varies with month, latitude and longitude, but the vertical structure of the aerosol mass mixing ratio follows a simple exponential decrease with height.

For both gases and aerosols, the climatology has been derived from the CAMS reanalysis but with a slight tuning to account for known deficiencies in certain locations of the globe.


Atmospheric chemistry is not yet included in the IFS.  Aerosol is not considered in the cloud microphysics (e.g. condensation nuclei) within the operational IFS - this may be important for weather is worth stressing but the impact is difficult to assess.

Users are advised to keep themselves updated about changes to the radiation scheme through the ECMWF Newsletter and web site.




Note that before the introduction of IFS Cycle 43R3 in July 2017, an older aerosol climatology was used that considered fewer aerosol species and did not include the dependence of optical properties on relative humidity.  

Additional Sources of Information

(Note: In older material there may be references to issues that have subsequently been addressed)

Amended/Updated 22/03/21 - Clarification