Research

The Acid Rain Problem

On the east side of Penn State's forestry building stands a Norway Spruce 40 feet tall. Twenty years ago, according to Joe Gardner, Penn State tree surgeon for 38 years, the tree was bushy, green, full of healthy cones near the top, and, in the characteristic manner of a Norway Spruce, the lower branches drooped slightly.

Today, many of the branches hang straight down. Branches, bare except for tufts of needles at the bottom, dangle in the wind like pendulums. Aborted cones—small, dark brown, unopened—spot the tree at all heights, to within six feet of the ground. The bald trunk is visible from across the east lawn.

Trees in Scandinavia, western Europe, southeastern Canada, and the northeastern United States show the same symptoms, eventually dying from the phenomenon called "forest decline." I had heard people blame forest decline—along with the death of aquatic life, reduction in yields of certain crops, and the deterioration of European cathedrals and Greek temples—on acid rain.

I wondered if the charges were true. To find out, I talked to some of the 20 or so scientists at Penn State—meteorologists, hydrologists, biologists, and plant pathologists—whose research touched on the subject. Every time I asked about this thing that scientists, politicians, and the press carefully call the "Acid Rain Problem," I became more confused.

Finally, I went to see someone I'd heard had a broad viewpoint—an engineer who had been an atmospheric scientist in Ohio, a state as embroiled in the acid rain controversy as Pennsylvania. Tomas Seliga had come to Penn State last September as associate dean for graduate studies and research in the College of Engineering. At Ohio State University, he had organized the First International Symposium on Acid Precipitation and the Forest Ecosystem in 1975 and had served on the Governor's Scientific Advisory Task Force on Acid Rain.

First I told him about the Norway spruce. I had asked John Skelly, a plant pathologist, about the tree, and he had answered with the story of when Bernhard Prinz, a scientist in the forefront of forest-decline research in West Germany, had visited Penn State. "As we were walking by that tree, Prinz said, 'There it is.' I said, 'There what is?' He said, 'Waldsterben.' That means 'forest death.' I looked at the tree and said, 'My goodness.' We looked back and forth from the tree to each other. Sure enough, it showed all the classic symptoms of the early stages of decline. I was somewhat surprised—I walked by this tree every day and hadn't noticed it."

"The Germans right now," Skelly had continued, "think waldsterben results from exposure to a combination of ozone—ozone is involved in smog—and acid rain. The ozone enters a needle and causes the cell membranes to leak or collapse so that the nutrients can be leached out by rainfall. Acidified rain may cause more leaching. Their evidence for this is still circumstantial—too circumstantial to convince me—but we have ozone in central Pennsylvania, and our rain is also acidic. We're trying to put together a collaborative study with the Germans to see if the symptoms they've described and the ones we've seen are the same. Then we could look at the ozone-acid rain interaction here."

Seliga sat very still while I spoke. His hands were folded in his lap, his legs crossed. He is robust, athletic-looking. Thick dark brown eyebrows and large, wire-rimmed glasses almost hid his partly closed eyes. At first I thought he wasn't listening, or that he was bored: He didn't nod or smile or follow my body motions, as one usually does in conversation. But as he began to speak—slowly, thoughtfully—I realized that he had been listening very closely. He had been synthesizing my questions into the context of what he knows about this unwieldy topic.

"People in Europe have been talking about acid rain—more appropriately acid deposition, because acid is present in not only rain but snow, fog, and dry particles—for a long time," he said. In 1872, the British chemist Robert Angus Smith coined the term "acid rain" in Air and Rain: The Beginnings of a Chemical Climatology. Smith had taken careful chemical readings of rain in Britain and Germany over a period of 20 years during the Industrial Revolution. He found high levels of sulfuric acid, sometimes as high as 21 parts per million; he attributed them to the burning of coal.

"I wasn't aware, as most U.S. scientists were not, that there was an acid rain problem, until Sven Oden, a Swedish soil scientist, and other Scandinavians raised the issue at a United Nations conference in Stockholm. Oden presented evidence that precipitation in Scandinavia was becoming more acidic and asserted that, based on trajectories of air masses, the acid rain came from emissions from coal burning plants in England and central Europe.

"Today, scientists in North America are advising policymakers on the best strategy in dealing with acid rain. So besides trying to understand how the natural world works for the sake of knowledge, they also have to answer to policymakers. That forces them to present the best evidence they have, even, sometimes, before they feel that it's ready to present, and it also forces them to take sides in a debate that has gone far beyond questions of science and technology. The federal government has spent more than $140 million in the last three years on acid rain research, and some scientists question the direction research is going."

"But let's start at the beginning," Seliga said. "What was your first question as a student of the 'Acid Rain Problem'?"

"How can we tell if the rain is becoming more acidic?" I said.

I had asked Bob Long, a doctoral candidate who, with Don Davis, a plant pathology professor, is studying forest decline in Pennsylvania, which has the dubious distinction of receiving the most acidic rainfall in the United States. Davis and his students, working with the Oak Ridge National Laboratories and the U.S. Geological Survey Tree Ring Lab, have analyzed more than 1,000 core samples from pines, hemlocks, oaks, white ash, black cherry, tulip poplar, pignut hickory, and basswood.

Long, a tall, soft-spoken young man, wears the classic wire-framed glasses preferred by hunters, outdoorsmen, and other iconoclasts. "If you're talking about the northeastern United States and southeastern Canada," he had said, "the answer is, we don't know that the rain is becoming more acidic. As a matter of fact, in the last decade the acidity of rainwater in the eastern United States may have actually decreased because the Environmental Protection Agency reduced the allowable levels for sulfur emission with the Clean Air Act of 1970.

"It's not a simple picture, though. What we wonder about are long-term trends: 25 years, 50, 100 years ago, to the time before we started burning coal in this country. No one was measuring atmospheric chemistry in the United States then, so we have to use indirect methods—like looking at what the trees recorded.

"See this? It's an increment core from one of the oldest white oak trees in Pennsylvania." The core looked like a 2-foot drinking straw, light brown, with dark brown lines irregularly spaced about every millimeter. It had been sanded flat on one side, polished, and mounted on a larger stick of wood. Long had taken two cores from each of the 33 trees he is examining in a stand of white oaks, aged 130 to 425 years, in Rothrock State Forest. He knows the size and species of each tree within a certain radius of the select 33, and the slope, aspect, elevation, and soil chemistry of each tree site.

"There are 425 rings here, one for each year. If the center of this tree hadn't rotted away in later years, we'd probably see that in the first 20 years of its life, the tree grew at its fastest rate. And see here?" He pointed to a spot about half way up, where the lines were bunched together for half an inch. "This could have been a local drought in the 1820s. Rainfall, of course, affects growth. So do temperature, competition for sunlight, insects and diseases, and soil fertility. A tree grows at a different rate depending on its size and age. When you start looking for places in the record where human factors have reduced growth, you have to account for the natural stresses first.

"Through statistics, we've found out something very interesting about the 1950s: About half of the trees from the old-growth stand in our study show a slowed or decreasing growth trend. So far, we've been able to discount advancing age and increasing size, two of the most likely natural causes. We can also pretty much rule out competition for sunlight because it's more stochastic—more random—in a stand like ours of trees of various ages. Insects or diseases are also more random. They'll affect one tree first, then spread to others. Exceptions would be the gypsy moth or the fall web worm or the Eastern tent caterpillar, but those outbreaks are noticeable—the ones in recent years have been well-documented by the state foresters.

"What I'm doing now is climatic modeling, using monthly temperature or precipitation records or both to model the climate and predict tree growth. What modeling lets you determine, finally, is what percentage of your ring width variation can be accounted for by climate.

"My modeling approach for white oaks is a variation on one Ed Cook of the Lamont-Doherty Geological Observatory did for red spruce. That model is based on an earlier one he helped develop at the University of Arizona: They wanted to use tree rings to see if there was a connection between sunspots and drought. To build a model, you take the tree-ring measurements and the weather data for each year—we have good monthly temperature and precipitation records for this part of Pennsylvania back into the 1880s. Then you adjust your equations until they accurately describe the observations, that is, the weather data successfully predicts ring width. When the model is accurate for 1900 to 1930, say, you verify it by using temperature and precipitation to predict the tree-ring widths for the next 20 years. I'm just barely starting the modeling for these 33 trees, but when Cook did his red spruce, he found that after 1968, the predictions and the observations didn't match. The trees were not growing as well as the model predicted."

As I relayed what Long had told me, Seliga blinked his large eyes slowly and pushed his glasses up a little on his nose. "So, according to what you heard, we don't know if the rain in Pennsylvania is turning more acidic, but we do know that some trees show an unexplained decline in growth starting in the '50s or '60s. What was your next question?" he asked.

"I thought I needed to know more about rain, particularly, what there is in rainwater that makes it acidic." I went to two meteorologists with this question. The first was Rosa de Pena, who had monitored acid deposition as part of the National Acid Precipitation Assessment Program. A large window in her office, on the fifth floor of Walker Building, commands an impressive view of clouds and sky.

"What is usually meant by acid rain," she began, "is rain—or snow—with a pH lower than 5.6." The pH scale runs from zero to 14: Seven is neutral, below seven is acid (lemon juice is pH 2.3), above seven is alkaline (baking soda is pH 8.2). A decrease in one pH point represents a tenfold increase in acidity. "'Clean' rain," de Pena explained, "is acidic—it has a pH of about 4.5 to 5.6—because of the carbon dioxide and other acid-forming substances that are always present in the atmosphere. Rain of pH 5.6, however, is seldom found today in the northeastern United States or in western Europe. The average values there are around 4.0.

"Besides carbonic acid from carbon dioxide, sulfuric acid and nitric acid are the dominant acids in rainwater," she continued. "Sixty to 70 percent of the acidity that is deposited—wet or dry—is due to sulfuric and 20 to 30 percent to nitric acid. These acids are formed when nitrogen oxides or sulfur dioxide meets with what are called 'hydroxyl radicals'—an atom each of oxygen and hydrogen. Both of these, hydroxyls and ozone, are always present in the atmosphere.

"Sulfur dioxide reacts with a hydroxyl or with ozone to produce bisulfite, an unstable molecule, which immediately reacts again with water molecules to produce sulfuric acid. Nitrogen dioxide takes only one reaction with a hydroxyl or ozone and water to produce nitric acid. These reactions happen even in the dark, but they are helped along by sunlight. That's why rain is much more acidic in the summer than in the winter.

"These tiny particles of sulfate and nitrate, then, become dissolved into rainwater in two ways: Either tiny water droplets scavenge them in clouds, or larger drops scavenge them on the way down. We know that part of the nitrate is scavenged below the cloud because the concentration of nitrate starts to decrease with continual rainfall in a particular spot. Sulfate levels, however, don't change very much no matter how long a storm goes on. The rain has sulfates even after the air below the cloud is cleansed of particles. The scavenging seems to go on mostly in frontal and cumulus clouds—the tall ones—because there is just more time for the process to occur."

"The problem with talking about acid rain," said Charles Hosler, "is we don't know what's going on up there." Hosler is a meteorology professor, member of the EPA Science Advisory Board, chairman of the board of Atmospheric Sciences and Climate for the National Research Council, and Penn State's vice president for research and dean of the Graduate School. He is admired for his phenomenal memory for names, dates, and numbers; glasses magnify his eyes to large, blue ovals.

"The earth is a dynamic chemical system," he continued. "Changes in weather, the power of the sun, water vapor, volcanoes, ocean currents, vegetation, and the biota, too, make this chemical mixture we call the atmosphere so complicated that we are only beginning to understand it.

"Anthropogenic sources of sulfates and nitrates—those resulting from human influence on nature—may be important, but when you think about all the other pollutants we're putting into this shin skin of gas we live in, methane, carbon dioxide, hydrocarbons, reacting in about 75 chemical reactions that we've identified so far—all of these are important in what ultimately produces acidity in the atmosphere.

"I am not an atmospheric chemist, but I've talked to most of the best in the world and they don't know what's going on. For example, if you look at a map that shows the acidity of the rainfall all over the world, one of the surprises is that rain is more acidic in the Falkland Islands than it is in Pennsylvania. They're not burning any coal down there. The people I've talked to think it's due to ocean processes. The ocean, as you know, covers two-thirds of the globe. It's a sink—or a source—for many of the chemicals in the atmosphere. A shift in ocean currents or an upwelling of the tides can radically change atmospheric composition in a relatively short amount of time. The cores they've drilled into the Antarctic and the Greenland ice sheets show marked fluctuations in acidity over history and prehistory, before any human influence."

Seliga shifted slightly in his chair. "How did you respond to those arguments?"

I had read a 1983 paper by Antonio Lasaga, a geochemist then at Penn State and now on the faculty at Yale, on the sulfur cycle, I told Seliga. It seemed to underscore the complexity Hosler had stressed. Lasaga had calculated the amount of sulfur in the air, water, and earth at any one time: the amount that is released to the air through evaporation, weathering, or volcanic eruption; the amount that falls from the air in rain; the amount taken up by the sea and land and deposited in sediment or siphoned through the ocean floor at the midocean ridges. Two sulfur reservoirs—fresh water and igneous and metamorphic rock—Lasaga found, were not at a steady state; that is, the fluxes into them did not equal the fluxes coming out. On the other hand, the oceans were balanced if the input due to humans was not considered. "If a particular reservoir is not at a steady state, one task of the geochemical cyclist is to decide whether a source or a sink has been left out or not appraised properly or whether there is a real imbalance in the system. Obviously," he concluded, "more work is needed on the sulfur cycle."

But I had also read an editorial by Philip Abelson, the former editor of Science, I told Seliga, that contained what I thought was a persuasive counterargument. "The phenomenon of acid rain is not new. It has been active for more than a billion years," Abelson wrote in the July 8, 1983, issue. "In addition to carbon dioxide, other substances contribute to acidity. About as much sulfur compounds are released worldwide to the atmosphere naturally each year as are put there by humans. In islands thousands of kilometers removed from industrial activity and presumably unaffected by it, rain with pH 4.7 is common. Soils having a pH of 3.5 are formed without human participation in the process.

"What is new from a geological standpoint," Abelson wrote, "is large-scale burning of fossil fuels. This activity and its effects are concentrated in a relatively small area of the globe. There the anthropogenic contribution of sulfur oxides exceeds that of nature by factors of 10 to 20. Annual precipitation is often equivalent to 20 to 50 kilograms of sulfate per hectare. Nitric oxides play an important role in the conversion of sulfur dioxide into sulfuric acids, and they contribute about a third of the total acidity of the rain."

Seliga nodded. "Did you believe, then, that even if sulfates and nitrates are not the only chemicals leading to acid rain, we still need to examine our role in contributing them to the atmosphere?"

"Yes."

"So, where did this lead you?"

"How much of the sulfates and nitrates in the atmosphere are our fault? I found a report by the National Academy of Sciences in 1983 that concluded that 90 to 95 percent of the acid rain in the Northeast comes from industrial smoke and car exhausts. And a 1985 book called Going Sour by Roy Gould, a biophysicist and Harvard research fellow who did a three-year scientific review and policy analysis of acid rain, says that more than 95 percent of the sulfur emitted in the eastern United States is from anthropogenic sources, mostly coal-fired power plants. Ninety percent of nitrates are from these sources. Of that 90 percent, 56 percent comes from stationary sources like smokestacks and industrial and residential boilers, since coal can contain more than 1 percent nitrogen by weight, and 44 percent from mobile sources like automobiles. Gould says his calculations were based on 'an understanding of the chemical reactions that sulfur and nitrogen oxides undergo in the atmosphere,' and a quantitative tally, or 'budget,' of how much sulfur and nitrogen is emitted from various sources and how much returns to the earth.'"

"So, as a student of the subject, were you convinced that the burning of coal and other fossil fuels is a major source of the sulfates and nitrates that are ultimately deposited as acid rain?"

"I suppose."

"Then we've come to the toughest question yet, right?"

"Right. Can we identify specific plants or even regions of the country that are releasing the most sulfates and nitrates?"

"I tried to answer that one myself," Seliga said. "And I used the best technique we have available right now: transport models.

"Transport models are mathematical models of how pollutants travel, are chemically changed in the atmosphere, and deposited on the ground. The models come in three types: single source or one smokestack, and long-range, where plumes travel further than a hundred miles. To draw the most realistic picture of the role of Ohio in the production of acid rain in the northeastern United States and southeastern Canada, my students and I combined a multiple-source model and a long-range model.

"Basically, the shape of a plume of gases and particles—which often have more gas adhering to their surfaces—depends on the temperature of the gas, the size and shape of the particles, the height of the smoke stack, and the wind speed and direction. Generally, a plume keeps its shape better in cool weather or at night than in warm weather or in the daytime because there is less of an updraft of warm air, and therefore less mixing. In the summer, with a wind speed of, say, 10 miles per hour, the concentration of sulfur dioxide in an average plume might be cut in half 3,500 miles away from the source. In winter, it could travel twice as far before dissipating that much.

"But as Charles Hosler pointed out to you, atmospheric movements are extremely complicated, and our models cannot take everything into account. For example, we can't put storms into a model because we can't adequately describe vertical motion. Also, it is still very difficult to get good data about the weather on a national or international scale: There are inconsistencies in rainfall data that just shouldn't be there; and with wind data, since readings are generally taken only every 24 hours, we are missing important information about speed and direction between readings."

"Then, if you can't pinpoint the sources of the sulfates and nitrates, and if we don't really know what happens in the atmosphere to cause them to come down as acid rain, and if we don't even know how much of the problem is caused by people and how much by natural sources out of our control, why even bother?" I asked. "Why not just wait and see if acid rain turns into a real, direct threat to human beings before we start worrying about it?"

"You said you spoke with people who study the effects of acidity on crops, aquatic organisms, and soil, right?" Seliga asked. "Didn't they give you any hints why we shouldn't wait?"

First I had spoken to Eva Pell, a plant pathologist who studies the effects of air pollution. Her short, dark hair and prominent cheekbones would give her face a decidedly strong look if it weren't for her winning smile. With funding from the U.S. Department of Energy and the Electrical Power Research Institute, she has tested the effects of ozone, acid rain, and the combination of ozone and sulfur dioxide on potatoes.

"We couldn't find that acid precipitation had any effect on Norchip potatoes, an important economic crop in Pennsylvania," Pell had said. She uses two greenhouses at Penn State's Rock Springs research station to apply simulated rain to potato plants. Each greenhouse is 30 feet wide, 88 feet long, and 14 feet high. It is mounted on rails so that, as soon as a drop of rain hits a sensor, the house closes. Three times a week, a rainshower begins inside—with rain of a carefully monitored acidity.

"We've run the test two summers and have not seen any effects on yield; total solids—which are basically starch; sugars; or total glycoalkaloids—those are bad, the green areas you occasionally see that make potatoes taste bitter. But just because we didn't find an effect on this variety of potato, you can't say categorically that there isn't any. That is dangerous thinking.

"My sense is that while we may find some negative effects—probably on yield—we're not going to find it the way we're looking now. It's just not compatible with the way plant pathologists do things to say, 'Hey, there's something out there that might be pathogenic. Let's see if it is.' The way we usually work is, a farmer comes to us and says, 'My grapes look like heck' or 'My tobacco has holes in it' and then we go look. And when we can't isolate a fungus, can't isolate a bacteria, can't isolate a virus, we start testing the air.

"There's a better approach, I think—looking at interactions. This summer, for instance, we'll be asking, Does acid rain increase the rate of leaching pesticides? Does it increase drought sensitivity of corn? Others have found significant answers to questions like these."

Ihad also talked to biologist Bill Dunson. In 1970, Dunson and his student Randy Packer discovered how acid conditions killed fish; their paper has become a landmark in the study of acid rain's aquatic effects.

"There is a misconception that mucus on the gills suffocates fish when they are exposed to acidity," Dunson had said. "You see pictures of the gills covered with mucus and it sure looks like that's what killed them—it's such an obvious symptom, I'm sure that's why the myth still persists. But if you look closely at the physiology, you see that the mucus is just a symptom of underlying gill damage that leads to a massive loss of sodium—salt—through the gills. One of the duties of gills is to control the sodium level in the blood: They take sodium out of the water and they slow the loss of sodium from the blood to the water. High acidity in the water damages the membranes of the gill cells and allows the sodium to leak out."

Dunson, reticent until prodded, walks with a slight stoop, as though concentrating too hard on things within to bother with the banalities of campus life. His fair, curling hair falls to his shoulders. When I continued asking about acid rain, he and his student Joe Freda, whose speech pattern reflects his New Jersey origin, launched into a debate, Dunson playing devil's advocate.

"Why try to understand sodium leakage from the gills or any of these other physiological things? All you need to know is whether the fish die."

"It's not a matter of them just living or dying," answered Freda. "The environment is so complex that no bioassay can unravel when they'll live or die. There are too many different factors affecting it. When you lime a lake to neutralize the acid, for example, it's only good for a couple of years and then you get an even more drastic decline in pH since the buffering capacity is reduced.

"I would approach it from the other way. Rather than liming the lakes, I would greatly increase the tolerance of fish. If you knew exactly what killed the fish . . ."

"But it's not just the fish. The whole food chain is disrupted. If there are no organisms for the fish to eat . . ."

"Fish are more sensitive than most of the other things."

"Naw. If you look at the data, in some of these lakes, the trout are still there, but there's no food for them to eat."

"That only happens when you have large fish that can live a long time essentially without feeding. But there are crayfish that do very well at low pHs and all kinds of insects that can survive under those conditions. If nothing else, you could feed the fish artificially."

"But what the fish people care about in Canada and the Adirondacks are the lake trout. Lake trout eat shiners and the shiners disappear under acidic conditions before the lake trout do. You'd have to engineer whole food chains."

Dunson nodded. "That's exactly what we're talking about. Most regional acid rain studies," he continued, turning to me, "stop short of using the most sophisticated means of deciding whether or not acid rain is affecting the ecological balance. Apparently, some people feel that studying the physiology of poisoned fish is not useful—it is enough to know that the fish die. But we have to know how and why the fish die to diagnose whether acid rain is at fault and to find a way of mitigating its effects. Just think about the battery of tests that are run on you when you enter the hospital with an illness. Why not use the same technique on a sick lake?

"Research on the effects of acidity cuts across many different, highly specialized scientific fields, so it's important to attempt to understand other disciplines, or at least those that are related to your work. You have to learn to look closely at all aspects of the database. With aquatic systems, it's not enough to do field surveys and water chemistry, which is how most of the federal money is being spent—seeing which lakes are acid, which lakes don't have reproducing fish populations, which economically important fish are living or dying—or to spend years actually adding acid to lakes to see what happens. It's not enough to know that more than half of the lakes in the Adirondacks have pH values below 5.0, and that 90 percent of these have no fish—even if you do know that between 1929 and 1937, only 4 percent of the lakes were below pH 5 or without fish. You've got to do detailed physiological studies in the field and in the laboratory to understand why the fish are responding this way.

"You also need to ask what happens to other organisms. You need to know that by liming a lake, which they're doing in many lakes in the Adirondacks, you are, by mistake, making wood frogs' eggs unable to hatch. The embryos can't get out of the egg, so as they grow, their spines start to curl. Some eventually do get out, but then they can only swim in circles. So you're helping one species while hurting another."

Adds Freda, "There are lots of habitats that are naturally acid. Most of Canada is naturally acid, much of the Atlantic coastal plain and the Amazon River basin are naturally acid. Many lakes have sphagnum bogs on the banks—sphagnum moss can put out a lot of acid. To animals, acidity is not a new phenomenon. We should look carefully at those natural systems."

I had, in fact, heard of the sphagnum-moss effect before. A handful of moss can acidify 300 times its weight in water, I'd read. According to the Wall Street Journal, a public utility in Wi