The WMO's Global Atmosphere Watch: Co-ordinating long-term atmospheric chemistry in the new millennium

Many urgent environmental problems confronting society, such as global warming, depletion of the stratospheric ozone layer, acid rain, urban pollution and transport of hazardous material are connected with the man-made changes in the state and composition of the atmosphere and its interactions with other environmental media. Within the United Nations system the World Meteorological Organization (WMO) has a continuing responsibility for providing authoritative scientific information and advice to its 185 Members on the state and behaviour of the earth's atmosphere and climate using a number of its operational observation networks, one of which is the Global Atmosphere Watch(GAW).

The GAW system is designed to co-ordinate two related atmospheric chemistry environmental problems: 1) To understand the relationship between changing atmospheric composition and changes of global and regional climate 2) To describe the regional and long-range atmospheric transport and deposition of natural and man-made substances.

The GAW measurement programme includes ozone (total column, vertical profile and near the surface), greenhouse gases (CO2, CFCs, CH4, N2O), solar radiation including UV, aerosol characteristics, reactive gas species (SO2, NOx, CO), chemical composition of rain, radionuclides and meteorological parameters. To ensure the required quality of data a number of measurement manuals have been and are being prepared and a data quality assurance/quality control plan for GAW has been recently developed.

To collect, process, analyse and distribute data obtained from the GAW stations, six World Data centres have been established by WMO: on ozone and UV (Toronto, Canada), greenhouse gases (Tokyo, Japan), precipitation chemistry (Albany, USA), solar radiation (St. Petersburg, Russia), aerosols (Ispra, Italy) and surface ozone (Kjeller, Norway). The GAW data are regularly published and are available directly from the Centres upon request to all organizations, scientific institutions and individual scientists.

A most important aspect of the GAW has been the establishment of Quality Assurance Science Activity Centres (QA/SAC) to oversee the quality of the data produced under GAW. Four centres have been established in Germany, Japan Switzerland and the United States. The QA centres play a major role in training, quality control and establishing protocols for measurements. In co-ordination with the QA/SACs, system of World Calibration Centres have been designated for specific measurements.

An overview of the GAW programme will be given with special emphasis on the new plans and activities taking place in the next decade.