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A new weapon in the war against acid rain

Julius Chang is at work on a project that could answer tough questions about how to reduce the acid-rain threat to lakes, streams, and forests. Dr. Chang is in charge of building an elaborate computer model here at the National Center for Atmospheric Research (NCAR). This project for the first time will link state-of-the art meteorology to pollutant chemistry and apply them to the phenomenon of acid precipitation and its less-well-known counterpart, acid deposition in dry air. The model, which will simulate the skies over the United States and Canada, will be on line in 1987.

Basically its task is to predict how air pollutants spread and chemically change under various weather conditions throughout North America.

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Dr. Chang is hoping the project will succeed where others have failed. In Washington, several proposals for reducing emissions that contribute to acid rain have been formulated, but they've gone nowhere -- partly because the Reagan administration, together with the representatives of smokestack America, insist more information is needed before costly new regulations are adopted.

The phenomenon of rain, snow, and fog that turns litmus paper red has become one of North America's most hotly debated environmental issues. Earlier this week President Reagan and Canadian Prime Minister Brian Mulroney announced that a team of special envoys will jointly study this issue, which has become a bone of contention between the two countries. On March 6 Canada had unveiled its own plan designed to slash the air emissions that contribute to acid rain by 50 percent over the next 9 years.

Precisely how to achieve a significant reduction in acid rain is a dilemma with no easy answer. This is true in part because it isn't yet possible to trace the sulfates and nitrates that turn to acid in the atmosphere back to their sources.

As a result, traditional market and legal methods for dealing with the damage they wreak have proven ineffective.

Nonetheless, there's little doubt that rising acidity levels are linked to emissions from industrial smokestacks, automobile exhaust pipes, and residential chimneys. It's also clear that high levels of acid precipitation are harmful to many ecosystems. What is less clear is how to distinguish these effects from the natural variability of specific environments.

All the uncertainties explain why the project headed by Dr. Chang could be important. ``I'm not foolhardy enough to think that this will provide all the political answers, but the results it gives may alter the perception of the decisionmakers,'' he explains. Without hard scientific results, he continues, the political debate is constantly in danger of being sidetracked by peripheral issues.

Exploring what-if environmental questions can be expensive and risky, Dr. Chang points out. Among the suggestions that have been put forward for studying acid rain are these:

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Shut down the Midwest's coal-fired power plants or switch them to lower-sulfur coal for a certain period of time to see to what extent this would lower acid precipitation in the East. The Electric Power Research Institute (EPRI) recently calculated such an experiment would cost half a billion dollars.

Use radioactive tracers to chart the course of pollutants as they wend their way across the country. Public concern over radioactivity has kept this proposal purely theoretical.

NCAR's computer simulation, while not cheap, isn't potentially destructive, Chang points out. The ``acid deposition modeling project,'' as it is called, is a $5 million program supported primarily by the Environmental Protection Agency, with some contribution from the National Science Foundation.

The preliminary version of the program has been completed. Basically, the simulation consists of two parts. One handles the meteorology. The other deals with the chemical interactions of pollutants -- sulfates, nitrates, and ozone -- as they mingle with the atmosphere.

Past acid rain studies were less sophisticated. Their results are ``fairly good, if you average them over a long period of time, like a season,'' explains Frank Ludwig, a meteorologist with SRI International, who has worked on the issue for EPRI. But their failure to explain short-term variations in acid levels has undermined their credibility, he says.

The NCAR model will utilize all the latest science, reports Dr. Chang. The result is a tremendously complex piece of programming. In its first incarnation, the model will deal with only eastern North America. Ultimately it will be expanded to include the western part as well. Because the program has a high resolution of 80 square kilometers (30 square miles), only an area the size of the Midwest will fit in the supercomputer's core memory.

To get quicker but rougher estimations, the NCAR team is constructing a model within the model. It will have a coarser grid size and simpler chemistry and will be cheaper to run.

The modeling project is not without its critics. Some question whether it's practical to even attempt to simulate the complex processes associated with acid rain. Others accuse the Reagan administration of using the NCAR project as an excuse to postpone action on emissions.

Environmentalists ``feel enough is known now to justify emissions reductions,'' comments Chuck Epstein of the Environental Defense Fund, which has been active in researching this issue. ``Still, we think this type of research is valuable.''

An industry researcher agrees on that latter point: ``This is where it all comes together. Without it, all we've got is a bunch of pieces to a puzzle.''

As with any computer output, however, the results will be only as good as the data fed in. And here there are some serious concerns. Regular sampling of acid precipitation is going on at only about 50 stations across the US; some scientists feel 100 to 200 such sites are essential. Moreover, comparison of the data is complicated by the fact that several different federal agencies are taking the samples, each using its own procedures.

Another important problem, says SRI's Ludwig, is the lack of accurate records on the constantly varying amounts of sulfates and nitrates being discharged.

All of these problems will make verification of the NCAR model more difficult. The experts agree it will be a number of years before the model will gain enough credibility to influence national policy. Nonetheless, it may prove to be an irreplaceable weapon in the battle against acid rain.