Status report on the key climate variables technical supplement to the

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  Consistent operation of existing observing systems is necessary to detect the eventual recovery of the ozone layer, not expected before 2020.
  
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  New satellite instruments were started recently and will give a substantial increase in data coverage. However, long-term validation and consistency of these instruments needs to be ascertained.
  
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  There is a need for improved distribution and calibration of ground-based observations to support the use of satellite data for global monitoring of ozone.
  
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  Existing multiple data centres should be better integrated. Data should be the same at all centres. Data quality and consistency, as well as ease of use (different data formats, web-interface, quick-look capability, etc.) should be improved.
  
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  A strategy to correct existing records for known breaks and changes should be developed and carried through.
  

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  Current stations have a high density at northern mid-latitudes and in polar regions. There are very few stations in the tropics, or in the Southern Hemisphere.
  

Atmospheric aerosols are minor constituents of the atmosphere by mass, but a critical component in terms of impacts on the climate and especially climate changes. Aerosols influence the global radiation balance by directly scattering solar radiation and indirectly through influencing cloud reflectivity, cloud cover and cloud lifetime.

Aerosol measurements are component for Global Atmospheric Watch (GAW) baseline stations and contribute to the Integrated Global Atmospheric Chemistry Observation (IGACO) theme (whose main purpose is to promote closer co-operation between the space and ground-based measuring communities for atmospheric chemistry). The objective of the GAW aerosol programme is “to determine the spatio temporal distribution of aerosol properties related to climate forcing and air quality up to multi-decadal time scales”. The measurement sites are required to represent the major geographical regions, and to address mainly global climate issues. These regimes include clean and polluted continental, polar, marine, dust impacted, biomass burning and free tropospheric locations. However, chemical composition data or data on precursor species are not readily available for most of these sites and in many cases are not monitored at these locations.

Limited networks of sun photometers (e.g. AERONET) have collected relevant observations from which aerosol amounts and properties can be derived. Astronomical observations at night constitute the only long-term recorded archive of atmospheric turbidity, although the latter cannot be directly converted into precise characterizations of aerosol properties and density distributions.

Research orientated sites largely operate as single sites. In the absence of regular inter-comparisons of sampling and analysis methods, which is typically the case, integration of data from these sites is problematic. Research networks such as; AEROCE and ACE-2 Longterm in the North Atlantic, operated by the University of Miami (UM) and the Environment Institute (EI), Joint Research Centre (JRC), Ispra, Italy, respectively and the UM DOE network in the Pacific Ocean, are valuable and unique sources for aerosol chemical composition data for these regions. However, these sites have largely been closed down during the late 1990s.