The source contributions are expressed as the percentage of the average air concentrations; where these do not sum to 100% this is due to inaccuracy of methods.
after: Maenhaut, W., P. Cornille, J.M. Pacyna and V. Vitols 1989. Trace elem
Cartographer / Designer
Graphical production: Philippe Rekacewicz and Emmanuelle Bournay (GRID-Arendal)