Aerosol Optical Depth Measurements and trends from the Global Atmospheric Watch - PFR Network and aerosol homogenization initiatives

Multiwavelength aerosol optical depth (AOD) has been defined as an essential climate variable for the Global Climate Observing System (GCOS) and the Global Atmosphere Watch (GAW) Program of the World Meteorological Organization. It is the most important parameter related to aerosol radiative forcing studies. PMOD/WRC have developed the Precision Filter Radiometer (PFR) that has been used for long term AOD measurements under a GAW-PFR Network of sun-photometers started in 1995 at Davos Switzerland and from 1999 at other locations, worldwide.

Here we present an overview of the stations measurements till 2021 including station statistics and AOD trends.

An overview of the results of the long term GAW-PFR AOD series for four high altitude stations (Izana/Spain, Mauna Loa/USA, Mt. Walliguan/China and Jungfraujoch/Switzerland). Mean AODs at 500nm were from 0.01 up to 0.1 with small negative changes per year for all stations.

Also we present an overview of the homogenization activities performed by the world aerosol optical depth research and calinration center (WORCC) towards a harmonization of AOD measurements worldwide and some examples on uncertainties and effects on global trend analysis and satellite AOD validation initiatives.