1. J.H. Kolts, Eur. Pat. Appl. EP 306 944 (1989).
2. W.H. Affleck and T.P. Moser, US Patent 4 868 841 (1989).
3. A. Collins, J.C. Frost and P.J. Price, US Patent 4 914 071 (1990).
4. H. Falke and G. Strauss, US Patent 5 112 787 (1992).
5. Ambient Air Pollutants from Industrial Sources;Suess,1985