The World Meteorological Organization (WMO) instigated the Global Atmosphere Watch (GAW) programme in 1989 as a successor to the Background Air Pollution Monitoring Network (BAPMoN).
During a 1993 workshop it was recommended that Aerosol Optical Depth (AOD) measurements, conducted previously under BAPMoN, should be discontinued until new instruments, methods and protocols were established to collect AOD data of known and assured quality.
Based on a recommendation by GAW experts in 1995, the World Optical Depth Research and Calibration Center (WORCC) was established in 1996 at the PMOD/WRC as one of the Swiss conributions to GAW. WORCC has since been advised by the GAW Scientific Advisory Group for Aerosols (SAG)
. Twelve existing GAW stations were chosen for the deployment and operation of 12 "N" type PFRs, provided by the Swiss Government. WORCC was assigned the following tasks: