Acid rain: Codusion or conclusion? By Stanton S. Miller During the week of February 11-16, the NAPAP (National Acid Precipitation Assessment Program) sponsored an international conference at Hilton Head, SC, to review 28 state-ofscience-and-technology reports. Some 650 attendees, mainly scientists (including 100 from outside the United States), came to discuss and to reach consensus on the 15,000 pages of reports. Established by Congress in 1980 under EL. 96-294, NAPAP tackled the coflcting views on the causes, effects, controls, and cost of acid deposition. NAF’AP, one of a half-dozen big science limding projects in the United States, has entailed 10 years of research, cost the taxpayers $500 million, and occupied about 288 scientists involved with the science and technology of acid rain. Consensus building is a slow process; the NAPAP goal is to produce the Inte grated Assessment of the program by September 30,1990. On the last day of the symposium, after scientists had discussed their areas of concern at sessions earlier in the week, a half-day was spent on plenary session reports. One purpose of these reports was to indicate the points on which scientists agreed and the uncertainty in the specific state of the science and technology. Reports were given on aquatic, terrestrial, human health, visib~ty,and material effects; economic evaluation; emissions, projections, and control technology; atmospheric processes and deposition; and atmospheric models and emissioddeposition relations. For example, Report 25 looked at 100 technologies for controlling emissions and estimated the controls and costs for doing so. From 1972 to 1985 industry spent $180 billion on emission controls; the electric utility industry 618
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spent $60 billion of this total. It was reported that controls on new power plants would cost $340-450 per ton of coal burned. The flagship of the research effort is the modehg effort,called RADM (regional acid deposition model). This activity has been ongoing for eight years at a cost of $16 million for development and an additional $50 million to evaluate data and begin to use the model. One problem is that there is no clear conclusion for predicting future emissions. Another is that the model may not be ready for final analysis. For example, it is mainly used for sulfur
chemistry assessment; neither nitrogen nor oxidant chemistry is represented and involved in RADM. Uncertainties in the many modules of RADM and in the data need to be specified, and the final model needs to be tested. In any event, RADM probably cannot be used by p o l i c y d e n now. Gregory McRae of Carnegie MeIlon University was the invited reviewer for the evaluation of RADM. He said that it was very difficult to separate the seience from the use of the model for public policy decisions. Where do models fit? There are deficiencies in NAPAP because it did not define the goals to drive the science. What are the goals of the model? McRae said that in earlier discussions in the session we heard qualitative terms “good” and “great” regarding the use of models to predict future conditions. The uncertainty issues of the modeling effort were swept under the carpet. The uncertainties must deal with and include error bias in the data and the model. There are many additional functions for the model, according to McRae: present results of other species (ozone, PAN, and nitric acid); characterize uncertainty from aggregation; evaluate the effect of errors in emissions; develop a software audit. How do models agree with the observed data? Certain types of plots are unacceptable. McRae pointed out that you cannot separate the SO2 effects from nitrogen and VOC chemistries because they are all connected. The key issue in dealing with model evaluation is that there is measurement uncertainty and modeling uncertainty. The report needs to identify the source of uncertainty and the range of data. The RADM has not been the subject of a sensitivity analysis. In conclusion, McRae recommended that NAPAP define performance goals,
0013-936x190/0924-0618$02.50/0 0 1990 American Chemical Society
carry out external software audits, characterizeuncertainty, specify the actual reasons for this uncertainty, look at the role of the oxidant problem, and open up the analysis interpretation to other modelers (including scientists who are not modelers per se and policymakers who are looking to the scientists for answers). The visibility session involved historical trends from airport visibility data. According to this record of 1940-1980 data, the greatest visibility impairment occurs during the third quarter of the year. Although there was a decline in visibility impairment in the northeastern United States over this time span, there was an increase in impairment in the southeastern United States. A deficiency in this visibility area is that there is no correlation of visibility with emissions. (It was said to be in other Summary of Science and Technology reports!) Most of the visibility studies were done in the western United States, but the results are coupled with the source-receptor relationships. The reviewer Joseph Michalsky of the University of New York in Albany questioned what effect humans have had on visibility. The transition from diffuse to direct observation techniques has not changed much in the past 14 years. According to Michalsky, there is a recommendation that instrumental techniques such as the automated column extinction should replace the human visibility procedure. There is also the question, Where would we be without the airport data? What also has to happen is to correlate changes in SO2 emission with changes in visibility. Where do we go from here? A major uncertainty for those who do the Integrated Assessment (IA) is, How does light extinction change with a change in the mass concentration of sulfate? What is the organic aerosol concentration in the East? What is its effect on attenuation? What happens next? According to John Malanchuk, deputy director of NAPAP, generalists will overlook the SOST reports for the Integrated Assessment. The big question comes from James Mahoney, director of NAPAP Does it (presumably the big science program called NAPAP) make a difference? He said that the Air Pollution and Hazardous Waste Association (the old APCA) will sponsor a program in December in Pittsburgh to try to answer that question. After the Integrated Assessment report in September, this association will be doing an evaluation of the NAPAP program in December. Getting ready for the IA It is important to know the points on which scientists agree and to know the
uncertainties and disagreements in the science. Then policymakers could make decisions about the acid rain policy decisions and the NAPAP program. As mentioned above, the last half-day of the symposium was devoted to the plenary session. Most of the speakers in this session made limited comments assessing the agreement and disagreement in the science, used data and slides from earlier sessions, and failed to indicate areas of scientific agreement and areas of uncertainty. Hence, the plenary session was of little value in an assessment sense. However, there was one exception. Dixon Landers of EPA in Corvallis, Oregon, performed an excellent assessment of the aquatics effects (SOST reports 9-15). For example, for Report 10-about what is going on in ecosystems-he noted that the area of agreement included comments that the conceptual framework is complete and that major processes were adequately considered. Seven points of criticism included inadequate discussion of definitions; lack of quantitation of the process; lack of European references; lack of comments on nitrogen and aluminum; lack of microbial discussion; shortcomings of the models; and need for verification of flow paths. Dixon treated the summaries of science and technology for all reports in the aquatic effects series in similar fashion. His example and thoroughness were not emulated by other speakers in the plenary session. With on-site evaluation in the plenary session such as was heard at Hilton Head, it will be difficult for the NAPAP team to pull together its comments for the Integrated Assessment. Looking ahead Acid rain is one of the oldest environmental catastrophicproblems scientists have tackled; although it is one of the half-dozen big science projects funded over the past 10 years, it is still an unresolved issue. Despite the legislative outcome of the imminent Clear Air Act, it will take another 10 years in which the progress will be measured, if indeed we can agree on the measurement plan. It won’t be until then that the public can be sure that the research and legislation were needed. NAPAP is winding down; its final assessment is due in September. Does global warming promise to be the next environmental catastrophe? One hears that we do not know enough about the warming to take corrective action. Perhaps we need a major research effort for this area! Perhaps not. Stanton Miller is managing editor of ES&T.
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