Our changing atmosphere : proceedings of the 28th Liège International Astrophysical Colloquium, June 26-30, 1989 - Liège International Astrophysical Colloquium; Crutzen, Paul J.; Gerard, J. -C. (Jean-Claude); Zander, R. (Rodolphe) (Universite de Liege, Institut d'astrophysique, 1989)