Acid Deposition and the Clean Air Act Amendments of 1990: Did Science Play a Role? Schwartz, S. E.. American Geophysical Union Spring Meeting, Baltimore MD, May 23-27, 1994, paper A21E-04, Invited.

In 1990 Congress enacted and the President signed landmark legislation aimed at reducing acid deposition in the United States by 50% by the year 2004. This legislation followed, and was ostensibly based on, a major, decade-long program of geophysical research under the National Acid Precipitation Assessment Program (NAPAP), which examined the atmospheric processes governing the relation between emissions and deposition and the biological and chemical processes relating acid deposition to effects on natural ecosystems, cultivated crops, structural and ornamental materials, and human health. It has been widely viewed that as a paradigm for science influencing policy, NAPAP was a failure; that geophysical research benefited more from NAPAP than the legislation benefited from the research; that the legislation reflected more the political process than any clearly demonstrated need for deposition reduction and a correspondingly clear path leading from reductions in emissions to the desired reduction in deposition. Here I argue that the scientific understanding that resulted from NAPAP and similar programs in other countries played a major role in establishing the consensus that was necessary for this legislation to be enacted. This research showed that the emissions flux and resulting deposition flux of sulfur and nitrogen compounds in industrial regions greatly exceed the natural flux of these compounds; that there are critical values of deposition flux above which there is an onset of substantial ecological damage; that the zone of influence of a given emission source is sufficiently great (one to a few thousand kilometers) that controls over regions of similar scale are required to achieve deposition reduction and that local controls would not be effective. On the other hand the enacted legislation is in many respects suboptimal, in some ways we know about and in some ways we do not know about and will not know about, especially as funding for acid deposition research has been cut off, the problem having been "solved" by legislation.

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