The impact of aerosols on the atmosphere is widely acknowledged as one of the most significant and uncertain aspects of climate change projections. The observed global warming trend is considerably less than expected from the increase in greenhouse gases, and much of the difference can be explained by aerosol effects. Aerosols impact climate through direct scattering and absorption of incoming solar radiation and trapping of outgoing long-wave radiation as well as through alteration of cloud optical properties and the formation of clouds and precipitation. 

There is growing concern for the impact of aerosols on human health and interest by many sectors such as weather prediction, the green energy industry (regarding their influence on solar energy reaching the ground) and the commercial aircraft industry (regarding the impact of volcanic ash and dust storms on operations and aircraft).

Regional problems include potential impacts on human health and mortality and environmental impact such as visibility impairment. Major sources of aerosols include urban/industrial emissions, smoke from biomass burning, secondary formation from gaseous aerosol precursors, sea salt and dust. Outstanding problems include determining the natural sources of aerosols, and the organic fraction.

Various aerosol parameters, such as aerosol optical depth, are measured at Global Atmosphere Watch stations that strive "to determine the spatio-temporal distribution of aerosol properties related to climate forcing and air quality up to multidecadal time scales."  The main goal of the GAW Aerosol Programme is to enhance the coverage, effectiveness, and application of long-term aerosol measurements within GAW and with cooperating networks worldwide, by

  • Further harmonizing aerosol measurements
  • Promoting coordination of networks for in situ observations
  • Establishing a GAW aerosol lidar network in cooperation with existing networks
  • Contributing to the integration of satellite, aircraft, and surface-based aerosol observations with aerosol modelling
  • Encouraging greater data submission and utilisation of GAW aerosol data
  • Supporting near-real-time exchange of aerosol data

Worldwide, there are numerous aerosol networks, regional or global in scope. They are divisible into two types: networks driven by environmental policy frameworks, and networks driven by project-based research. The objectives, development, maintenance and financial structure of these two types of networks are very different and there are often limited interactions between them. The vision of the Aerosol Programme is comprehensive integrated sustained observations of aerosols on a global scale through a consortium of existing research aerosol networks complementing aircraft, satellite and environmental agency networks.