This centre receives and archives precipitation chemistry data and complementary information from stations around the world. Data archived by this centre are accessible via connections with the WDCPC database. Freely available data from regional and national programmes with their own Web sites are accessible via links to these sites. The WDCPC is one of six World Data Centres in the World Meteorological Organization Global Atmosphere Watch (GAW). The focus on precipitation chemistry is described in the GAW Precipitation Chemistry Programme. Guidance on all aspects of collecting precipitation for chemical analysis is provided in the Manual for the GAW Precipitation Chemistry Programme (WMO-GAW Report No. 160).