The World Data Centre for Aerosols (WDCA)
is the data repository and archive for microphysical, optical, and chemical properties of atmospheric aerosol of the World Meteorological Organisation’s (WMO) Global Atmosphere Watch (GAW) programme.  

“The goal of the Global Atmosphere Watch (GAW) programme is to ensure long-term measurements in order to detect trends in global distributions of chemical constituents in air and the reasons for them. With respect to aerosols, the objective of GAW is to determine the spatio-temporal distribution of aerosol properties related to climate forcing and air quality on multi-decadal time scales and on regional, hemispheric and global spatial scales.” 

GAW aerosol long-term observation core parameters:

  • Physical Properties:
    • particle number concentration (size integrated)
    • particle number size distribution
    • particle mass concentration (two size fractions)
    • cloud condensation nuclei number concentration (at various super-saturations)
  • Optical Properties:
  • light scattering coefficient (various wavelengths)
  • light hemispheric backscattering coefficient (various wavelengths)
  • light absorption coefficient (various wavelengths)
  • Chemical Properties:
  • mass concentration of major chemical components (two size fractions)
  • Column and Profile:
  • aerosol optical depth (various wavelengths)
  • vertical profile of aerosol backscattering coefficient
  • vertical profile of aerosol extinction coefficient

Additional parameters recommended for long-term or intermittent observation:

  • dependence of aerosol properties on relative humidity
  • detailed, size segregated chemical composition.

The extent of the observation programme varies between observatories networked in GAW. The observations are reported by the GAW observatories on a voluntary basis, while the station infrastructure is a contribution of the participating national authorities to the GAW programme.

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