Every Breath You Take 

Acid Rain

Acid Rain

Nashville is in a hole. The Cumberland Basin is an irregular oval approximately 50 miles wide, encompassing 5,000 or so square miles in the very center of Tennessee. Usually, the people who live there don’t realize they’re in a depression. From the center of the Basin, you can’t see the Highland Rim that encircles it. As you enter the bowl, the gradient seems slight. But it affects weather, and weather affects pollution, and pollution affects lives.

“The Central Basin tends to trap in our pollutants,” explains WKRN-Channel 2 meteorologist Davis Nolan. “Especially in certain times of the year when the winds aren’t very strong, as in the summertime, you can get an inversion set up. The atmosphere gets warmer with height, and that’s what caps in the air. Nashville becomes a miniature Los Angeles.

“It’s the same with the weather. We can have it snowing all around Nashville but not in Nashville itself snowing outside the Basin and raining inside the Basin.”

According to Nolan, our topography is one reason Nashvillians are required to get emissions tests for their automobiles. “When I moved here in 1981,” he says, “experts could already see the handwriting on the wall. People were saying that if we don’t do something about the pollution here in Nashville, the federal government is going to come in here and order us to. But what would we have done? Tell people not to drive cars? Dynamite away the Highland Rim?”

On any hazy August day, even without warnings from weather forecasters and health officials, you can tell that Nashville has air problems. But, like malls and interstates and chain restaurants, air pollution is part of what makes Nashville much like any other city in the U.S. at the end of the 20th century.

"The Inconvenience of the Air"

Air pollution is not a new problem. It’s existed at least in short-lived, localized, natural forms since before there were human beings to cough in response. But people, always tampering with the world around them, are masterful when it comes to throwing nature out of balance. Steadily increasing population has required the combustion of steadily increasing amounts of fossil fuels. The result is that, for hundreds of years now, the air we breathe has been growing increasingly dirty and dangerous.

The first recorded environmental legislation, enacted by King Edward I in 13th-century England, prohibited London merchants from burning coal while Parliament was in session. Like many such prohibitions, it didn’t go far enough. In 1661, the English writer John Evelyn wrote a pamphlet about the ongoing problem; its memorable title was Fumifugium, or, the inconvenience of the air, and smoke of London dissipated. Evelyn described a day on which “a presumptuous smoke issuing from near Northumberland house, and not far from Scotland Yard, did so invade the Court, that all the rooms, galleries and places about it, were filled and infested with it, and that to such a degree as men could hardly discern one another from the cloud.”

The problem Evelyn described did not get better. It got worse. During the Industrial Revolution, London’s choking fogs grew increasingly dangerous. In 1905, Harold Des Voeux, an English physician, formed the word “smog” out of a rear-end collision between “smoke” and “fog.” A quarter of a century later, he founded the Coal Smoke Abatement Society. Des Voeux was fighting an uphill battle. As usual, it took a disaster to raise public awareness of the problem and to galvanize people into action.

In 1952, a high-pressure system smothered London in smog. This was not a picturesque pea-soup fog. It was killer smog, and 4,000 people lost their lives. Four years later the British government enacted the Clean Air Bill, which prohibited the combustion of soft coal in London. The result, almost immediately, was much cleaner air.

“Clearly the whole reason that the air-pollution concern arose originally is because people were dying,” says Janice Nolen, program director for the Tennessee Chapter of the American Lung Association, and a member of the Association’s National Air Conservation Commission. “Up until the 1960s, we could see episodes of smog in large urban areas that had directly associated deaths. We still have that, only it’s not as obvious. Clearly, science shows that, as particulates are elevated, the risk of death increases. And of course not only death but chronic health problems.”

The tide began to turn in the U.S. in 1970, when Congress passed the Clean Air Act. It was amended in 1990, and revised standards for pollution limits went into effect last year. The new rules came about after the American Lung Association sued the EPA, because the agency was running years behind the mandated schedule for revisions. According to Nolen, the Lung Association is “good friends with EPA we work with them closely but sometimes you just have to sue people.”

The Clean Air Act demands that the EPA revise air-quality standards every five years, based on the latest research. Finally, in June of 1997, at a conference in Nashville, President Clinton announced his decision to tighten national air-quality standards for certain pollutants.

What Goes Up

Air pollution is not a simple issue. It exists in several forms, each with its distinctive sources and health consequences. To make the situation more complicated, the effects of pollutants are often felt far beyond the source of the emissions. Winds blow in the real world, not on maps. They ignore political boundaries.

The EPA defines toxic air pollutants as those that are “known to cause or are suspected of causing cancer, adverse reproductive, developmental, and central nervous system effects, and other serious health problems.” The tedium involved in tracking real pollutants across imaginary lines results in a never-ending headache for scientists and for policymakers. For example, Toxaphene, a pesticide popular in the South, has been found in the Arctic, concentrated in the fatty tissues of polar bears.

To understand the Herculean challenge of tackling air pollution, it’s important to realize the variety of its causes. Although other chemicals are known to be potentially dangerous, the Clean Air Act regulates 188 pollutants as hazardous. They range from heavy metals, including lead and mercury, through deliberately manufactured chemical compounds, including pesticides and PCBs, to industrial by-products such as dioxin.

An example will help demonstrate the way these toxins work. Mercury is a naturally occurring metallic element; in nature it takes the form of a heavy, toxic liquid. Nature does its part in producing atmospheric mercury through volcanoes, geysers, and even forest fires. But far greater amounts get pumped into the atmosphere by coal-fired power plants, incinerators that burn medical and municipal waste, and the type of cement kilns that burn hazardous waste. That’s partially because manufacturers use mercury in barometers, batteries, light switches, paints, and, most famously, thermometers.

Unfortunately, prolonged exposure to mercury, either through swallowing or inhaling it, can damage the central nervous system the central nervous system of humans, not just animals. The Mad Hatter in Alice’s Wonderland was mad simply because he was a hatter. For generations, hatmakers used mercury to treat the fabric used in their work.

And we and our fellow creatures don’t just encounter each day’s mercury emissions. The metal persists in the environment and concentrates as it climbs up the food chain. Every creature that eats a mercury-tainted plant or animal acquires much of the mercury that each preceding creature in the chain absorbed and passed along. That explains why the most heavily publicized mercury contaminations are usually associated with fish. Fish live fully immersed in their environment.

And mercury is only one example. Each toxin behaves differently. Some break down quickly and have a health impact only in their immediate surroundings. Many others, like mercury, persist in the atmosphere and accumulate in intensity. But we seldom experience air pollution as the impact of a particular pollutant. If we did, it would simplify both scientific measurement and the legislation that results.

Instead, we experience combinations and interactions of pollutants. When air pollution is discussed on the news, the terms you hear most often are “particulate matter,” “ozone,” and “acid rain,” with additional references to the natural phenomenon of pollen. Each of these problems requires its own studies and its own monitoring standards. And they gang up to cause more trouble than any one of them could generate on its own.

Particulate Matter

Particulate matter, sometimes referred to as “suspended particulates,” consists of those solid particles and liquid droplets that can be found floating in the air around us. The tiny particles scatter and absorb light, interfering with our ability to see objects at a distance and helping create the grim blur we accept as part of our urban lives. We describe it with the innocent term “haze.”

Besides being a national issue of great concern, haze is also an imprecise but vivid index to levels of pollutants. In general, because of greater amounts of pollutants and also because of higher levels of humidity, haze is a worse problem in the eastern than in the western United States. According to the EPA, visibility in the eastern U.S. should be roughly 90 miles, but pollutants have reduced that range to 14-24 miles. In the West, visibility has shrunk from an average of 140 miles to 33-90 miles.

Particulate matter comes from a variety of sources. Nature throws spores, pollen, spray, and fog into the mix, but human contributions are more ominous. Some come directly from utility and industry smokestacks and automobiles, but others are formed by the reaction of chemical compounds in the air.

Thanks to the variety of sources, the size of the particles varies greatly. More stringent standards for particulate matter now monitor particles that are 2.5 microns or less in diameter (roughly one-seventh the width of a human hair). In the past, the EPA monitored particles only as small as 10 microns. The reason for the new standard is growing scientific evidence that very fine particles pose a greater threat to human health, because they bypass the body’s defenses and penetrate deeply into the lungs.

The EPA is assuming the costs of such monitoring, in order to collect the data that will determine each geographical region’s compliance with the new standards. The EPA delegates authority for some programs to each state government, provided the state meets certain conditions. Tennessee, which meets the requirements for self-monitoring, has delegated local pollution-monitoring authority to the cities of Nashville, Knoxville, Chattanooga, and Memphis. In Nashville and Davidson County, the responsible authority is the Air Pollution Control Division of the Metro Health Department.

The Air Pollution Control Division expects to receive its first round of new monitors in late summer or early fall. In the meantime, they are determining three sites around Davidson County where they can install the new monitors. “These monitors are new to us,” says Rob Raney, the division’s director. “It’s going to take us a while to learn how to operate them properly. It’s a very complicated procedure, as far as handling these filters, because we’re dealing with such fine particulate in such minute amounts.”

Raney says his office will be using the state laboratory to weigh the collected pollutants. The facility will require a specialized weighing room, with controlled temperature and humidity. “There are problems with static electricity and so on that could change the weights appreciably,” Raney says. “The folks doing that work will have to be trained in proper procedures, wear the proper clothing, never touch the filters, use forceps and gloves. The filters have to be maintained in a controlled atmosphere prior to being weighed. Once we get the monitors up and running, we will probably officially begin our monitoring Dec. 31 or Jan. 1.”


Monitors for measuring ozone are already in place, because the EPA has required ozone-monitoring for years. The new requirements changed the percentage of allowable ozone and the methods of gathering and interpreting the data. For example, the old method of measuring ozone in one-hour blocks was found to be inadequate, because levels changed so much throughout the day. Now it is being measured in eight-hour blocks.

Ozone (which is, in general, what we call smog) isn’t directly emitted into the atmosphere. It’s a secondary pollutant, formed from the chemical reaction of two other pollutants, known as “ozone precursors.” In the acronym-infested scientific and bureaucratic world, these precursors have names that sound like Dr. Seuss characters-NOx and VOCs.

NOx (nitrogen oxides) are produced almost entirely by the combustion of fossil fuels especially in coal-fired power plants and industrial boilers and in cars and trucks. VOCs (volatile organic compounds), on the other hand, are produced mostly by motor vehicles and factories. Many commonly used chemicals, such as organic solvents, are VOCs. When exposed to sunlight and heat, NOx and VOCs undergo chemical reactions that help form smog. That’s why ozone levels rise during the day and go down again at night. For that reason, during the summer it is wise to exercise as early as possible, before the ozone level rises.

Not surprisingly, some people confuse the worry that there is too much ozone on Earth with the worry that there isn’t enough ozone in the upper atmosphere. The two are quite different phenomena. The ozone layer in Earth’s outer atmosphere protects our planet by absorbing harmful ultraviolet radiation. Its highly publicized depletion which is linked to the increasing incidence of skin cancers is occurring even as greater amounts of ozone are being produced by pollution down here where we live and breathe. And ground-level ozone is harmful to plants, animals, and people.

The EPA collects data about ozone to determine which geographical regions are in compliance under the new standard. Regions described as “nonattainment” areas are those parts of the U.S. that are not meeting the new standards.

Most predictions based upon the currently available data indicate that Nashville is unlikely to meet the new standards. If we prove to be over the limit, Metro’s Air Pollution Control Division will face difficult tasks determining where the NOx and VOCs come from and what can be done to reduce those pollutants and allow Nashville to squeeze in under the limit.

NOx are versatile villains, and they contribute to more than just ozone. They also unite with sulfur dioxide to form acid rain. Sulfur dioxide is a toxic compound primarily produced when power plants burn coal, oil, and natural gas. There are other sources too, but in the U.S. 70 percent of sulfur dioxide emissions come from power plants.

“Acid rain” is the common name for what is more precisely called “acid precipitation.” It can take the form of rain, snow, sleet, and even mist. (An even larger category, acid deposition, includes the fallout of dry particles.) Precipitation is considered to be “acid” when its pH balance is significantly lower than neutral.

The pH scale represents the acidity or alkalinity of a solution. It ranges from 0 to 14, with neutral solutions at pH 7. Higher values are basic (or alkaline), with the scale going up through ocean water and baking soda to substances such as ammonia. Lower values are acidic, moving down the scale to vinegar (pH 3) and lemon juice (pH 1 to 2) the ranges where acid rain shows up. The degree of acidity in acid rain varies, but “pure” rain, untainted by pollution, would have a natural pH of roughly 5.5.

Acid rain forms when sulfur dioxides and NOx combine with water vapor to form sulfuric and nitric acids. While still in the air, these substances contribute to haze and other health-endangering effects. Then, when they unite and fall to the earth as precipitation, they damage soil and plants and make streams and lakes too acidic to support their natural variety of plants and animals. In a parallel phenomenon more visible to most of us, acid rain causes the deterioration of monuments, buildings, and even automobiles.

Nor does it stop there. Acid rain can also pick up toxic metals as it filters down through soils, ultimately transporting them into streams and lakes. That’s one way such toxins accumulate in water and begin to climb up the food chain.

Some areas of the country receive more and harsher acid precipitation than others. Also, some regions are blessed with soil that is more resistant to acid rain, because it contains acid-neutralizing compounds. Much of the Midwest possesses this buffer. Less fortunate are thin-soiled mountain regions in the West, Northeast, and Southern Appalachians. For example, because of acid deposition, only a very narrow band in the Smoky Mountains has streams that are still capable of supporting native trout.


Although it hasn’t yet been regulated by Congress, floating around out there in the air, along with NOx and VOCs and the rest of the alphabet soup, is one of nature’s least popular contributions to summer discomfort pollen. It ranks high among the many natural and manufactured substances to which some people are allergic. Responses range from mild discomfort to crippling illness, and those unpleasant responses have inspired countless treatments.

Pollen consists of grains or spores containing the male contribution to seed plants. It’s produced by the anthers, and fertilization of the plant occurs when the pollen leaves the anthers and moves to the female pistils. Plants have evolved a number of ways of arranging this exchange of genetic information; sometimes it’s even carried by insects or birds. But the vehicle that most affects human beings is the wind that carries pollen to our eyes, noses, and throats.

Allergy seasons vary in different parts of the country, and different plants contribute pollen at different times of the year. In the southeastern U.S., the busiest culprits in the spring are trees elm, oak, maple, birch, and others. In the summer, we can mostly blame grasses such as timothy, redtop, and bluegrass. By late summer, ragweed is the major remaining villain left.

Although individual pollen grains are all but microscopic, in large quantities they are visible as a fine powder (usually yellow). Not surprisingly, this great mass of particles emitted into the air also contributes to the haze problem.

Taking the Air

While everyone should be aware of the hazards of air pollution, it is particularly dangerous to children because, pound for pound, they breathe in more air than adults do. Generally, children are more active, and have a higher respiratory rate, than adults. To make matters worse, their lungs are smaller; and they spend more time outside. The Lung Association offers advice about how to protect yourself and your children from the dangers of dirty summer air:

♦ Because children with asthma are especially sensitive to air pollution, watch for signs of undiagnosed asthma regular coughing, shortness of breath. Health officials consider asthma sufferers, because of their sensitive lungs, to be like canaries in a coal mine. Like senior citizens, all children under the age of 15-or-so, and people who suffer from chronic lung diseases such as emphysema or chronic bronchitis, their problems let us know when the condition of the air is growing dangerous.

♦ If your child does have asthma, learn to recognize what triggers an attack. Ozone can sensitize asthmatics, making them react more strongly to triggers.

♦ Keep track of air pollution levels. Usually you can find updates through TV, radio, and newspapers. Information can also be found in the online pollution index that the Metro Health Department updates twice daily. (Visit the Health Department Web site at www.nashville.org/health and it will lead you to the pollution index, or go directly to the index at www.nashville.org/health/ psipoll.html#pollution index.)

♦ If the weather report says the air is unhealthy, limit your child’s time in outdoor play. Plan the most strenuous activities for early morning, before ozone levels rise. Stay as far away as possible from highways and other air-pollution sources.

♦ Make sure your child’s coaches and camp directors are aware of the dangers of bad air, and have policies in place to protect the children when necessary. If your child has asthma, always make sure responsible adults know of the condition and take it into consideration especially on days with high ozone levels.

♦ Make sure your indoor environment is as healthy as possible especially when, on hot summer days, it becomes your only refuge from outdoor pollution. Keep it smoke-free, clean regularly to reduce dust and pests, and fix moisture problems that would encourage mold.

What's to Do?

Human beings breathe in an average of 3,400 gallons of air every day. It helps if it’s clean.

By the time you go to bed tonight, you can help assure that the air you breathe tomorrow will be a fraction less polluted than it might have been. The modern world still runs largely by burning condensed hydrocarbons that are stored in the remains of plants and animals that lived millions of years ago. Because electric utilities are a major source of air pollution, you could begin by reducing your electricity consumption.

Fewer lights left on, higher settings on thermostats these traditional bits of advice really do lower the amount of daily pollution. The modern variation on “A penny saved is a penny earned” is “A kilowatt saved is a kilowatt that doesn’t have to be produced by the combustion of fossil fuels.” (Granted, it isn’t as catchy as Benjamin Franklin’s line, but it’s more to the point.)

This summer, with the entire Southern and Midwestern United States looking like a textbook case in global warming, air-conditioning demands have climbed to record highs in many areas. Several utilities have encouraged voluntary reduction of electricity use by warning of the threat of rotating energy blackouts.

Every year, during summer or winter electrical peaks, Americans suddenly remember that energy is a finite resource. One factory manager, recently interviewed on National Public Radio, seemed astonished to report that his company had greatly reduced electrical consumption, thus reducing operating expenses (and the burden on utilities), without inhibiting productivity in the slightest. Because automobiles are another major source of fossil fuel emissions, lead-free gasoline is not enough. Other steps are necessary.

First of all, you could share a ride. But in Nashville, most Metro buses seem to stay half empty. Every vehicle left at home slightly improves the quality of the air you breathe during the day. If you can’t walk or bike or ride the bus, you can keep your car tuned up so that it performs better and wastes less gasoline. Better yet, any of these strategies to reduce air-pollution will also save you money.

Occasionally something works the way it’s supposed to.


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