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Unclassified OECD ENVIRONMENT WORKING PAPERSOECD Working Papers should not be reported as representing the official views of the OECD or of its member countries. The opinions expressed and arguments employed are those of the author(s). Working Papers describe preliminary results or research in progress by the author(s) and are published to stimulate discussion on a broad range of issues on which the OECD works.This series is designed to make available to a wider readership selected studies on environmental issues prepared for use within the OECD. Authorship is usually collective, but principal author(s) are named. The papers are generally available only in their original language -English or French-with a summary in the other language.Comments on Working Papers are welcomed, and may be sent to: OECD Environment Directorate 2 rue André-Pascal,