Humans have been pouring pollutants into the atmosphere ever since the discovery of fire; but volcanoes, forest fires, and even desert dust can add their particles to the mix, creating atmospheric conditions that are hostile to nearly every form of life on the planet. Human effects on the atmosphere translate in the long run into changing weather. This, effectively, is what is meant by the crisis of climate change.
Air pollutants fall into two main categories: primary pollutants, which cause a direct effect on the air, and secondary pollutants, which must first mutate into harmful substances such as acid rain and ozone, following a chemical reaction. Primary pollutants come from sources such as smokestacks and auto exhausts, doing their damage immediately on entering the atmosphere.
Approximately 6.6 million tons of pollution are pumped into America’s air every year. About 40 percent of it comes from industrial processes, and another 17 percent is emitted by automobile exhaust systems. Particles that can remain suspended in the atmosphere for years are called aerosols. If they’re small enough, they can be spread hundreds of miles from their sources by the prevailing winds in the upper atmosphere. The tiniest particles are able to slip right by your lungs’ defenses and cause allergic reactions and worse.
In cities the major pollution culprit is carbon monoxide (CO), an odorless, colorless toxic gas that results from incomplete combustion of fuel. Motor vehicles account for about two-thirds of carbon monoxide emissions in urban areas, although the figure can rise as high as 90 percent. Carbon monoxide harms humans and animals by reducing the amount of oxygen blood can carry. Since it can bond more easily with hemoglobin than oxygen, high levels of carbon monoxide in the blood are very difficult for the body’s defenses to remove. Low levels of carbon monoxide poisoning create flulike symptoms, while higher levels result in loss of consciousness, convulsions, coma, and finally death.
You may not think of carbon dioxide (CO2) as a pollutant; after all, your lungs produce it with each breath. But it’s also a by-product of burning fossil fuels such as oil, natural gas, and coal. Aside from being toxic if inhaled in large amounts, carbon dioxide has been identified as one of the major greenhouse gases.
The Environmental Protection Agency (EPA) has identified 188 chemicals that can cause serious effects on human health and the environment, and has assigned them the collective name of hazardous air pollutants, or HAPs. Exposure to these compounds can cause serious disabilities and illnesses such as cancer, diseases of the central nervous system, birth defects, and even death by large-scale releases. The major cancer-causing HAPs are 1,3-butadiene, polycyclic organic matter, benzene, carbon tetrachloride, chromium, and formaldehyde.
A major pollution disaster happened in Bhopal, India, in 1984. A release of deadly gases at a Union Carbide pesticide plant there killed at least 1,700 people and injured several hundred thousand others, many who experienced permanent physical disabilities, respiratory ailments, cancers, and multigenerational genetic damage.
Many manufacturing processes, including spray painting, semiconductor manufacturing, dry cleaning, wood finishing, and printing produce volatile organic compounds (VOCs), use a class of chemicals that easily forms vapors at normal temperatures and air pressures. Some of these gases are harmful when inhaled, and many of them are carcinogens. Others are readily soluble in water and can pollute not only the air but groundwater supplies as well.
VOCs are indoor hazards as well: they can be found in paints, solvents, household cleansers, and disinfectants, among other common supplies. Limited exposure can cause headaches and irritation of the eyes, nose, and throat. More prolonged contact can result in nausea; loss of coordination; and liver, kidney, and central nervous system damage.
Sulfur dioxide (SO2) is a pollutant that can be caused by erupting volcanoes, but it is more commonly created as a by-product of the burning of sulfur-containing fuels such as coal and oil, by the smelting of metal, by paper production, and by other industrial processes. Sulfur dioxide is a colorless gas that is odorless in small concentrations but has a strong smell at higher levels. In water, sulfur dioxide dissolves to form highly toxic sulfuric acid; in the atmosphere, it binds with water molecules and falls as acid rain.
The term acid rain is a misnomer in some cases, because pollutants don’t always fall to earth in a wet form. The earth’s gravity is constantly trying to pull anything in the atmosphere back to the surface, so acidic gases and particles can make their way to the ground without rain in a process called dry deposition. About half of all acidity in the atmosphere returns to earth in a dry form, so a more accurate term for acid rain is “acid deposition.”
Acid deposition can happen hundreds of miles from a pollution source. Particles swept up by the wind can often be transported across state and national borders, making air pollution a global problem, not just a local one. In the United States more than ninety billion pounds of sulfur dioxide and nitrogen oxides are released into the air each year. When this acid binds with water droplets and falls as rain, it carries pollutants into the ground and mixes with particles that have already fallen as dry deposition.
When acidic water enters streams, lakes, and marshes, it begins to lower their pH levels. Soil and water normally have some capacity to neutralize acid, but in places where the soils have low alkaline levels and precipitation has a high acid content, acidity can quickly overwhelm a watershed’s natural buffering capacity. As acid rain flows through soil it liberates aluminum, which is carried into lakes and streams along with polluted water. For fish, low pH and high aluminum levels are a deadly combination.
More than thirty years ago, scientists first became concerned when they noticed that even in remote areas, lakes that were once full of fish had become barren. The US Geological Survey was brought in to determine the reason, and eventually acid rain was pegged as the culprit. The survey established the National Atmospheric Deposition Program/National Trends Network (NADP/NTN), which collects rain and snow samples from across the country and monitors them for acid deposits.
The survey found that rain or snow falling in the eastern United States has a much lower pH level than precipitation elsewhere in the country. In addition, a National Surface Water Survey identified several areas where streams were especially sensitive to acidification, including the mid-Appalachian region, the Adirondack and Catskill Mountains, the upper Midwest, and mountains of the western United States. Acid rain was found to be the cause of acidity in 75 percent of acidic lakes and 50 percent of acidic streams.
The effects of acid rain aren’t limited to bodies of water; the low pH levels it causes in the soil can slow the growth of entire forests, make leaves turn brown and fall off, and even cause trees to die. In the eastern United States the Shenandoah and Smoky Mountain National Parks have been particularly hard hit. Atop Clingmans Dome in the Smokies a once-proud stand of conifers is now a ghost forest, its denuded trees covered with moss and lichen.
Although acid rain doesn’t directly kill trees, it weakens them by damaging their leaves and exposing them to toxic compounds in the soil. Just as it does in fish, acidity stresses trees and plants, making them more susceptible to disease or attack by insects, drought, or cold weather. In high forests such as those in the Smoky Mountains, pollution’s effects can be magnified and accelerated by the constant presence of acid fog, which acts to deplete essential nutrients in the leaves of plants and trees.
Acid deposition isn’t always noticeable, but it affects everything it touches, even buildings and automobiles. In our nation’s capital, monuments made of seemingly eternal materials such as marble are literally being eaten away by acid in the atmosphere. Marble is composed of calcium carbonate, or calcite, which is easily dissolved by even mild acid. Because many of our national monuments are made of marble or limestone, some are slowly crumbling as acid deposition takes its toll. Some of the buildings particularly affected are the Capitol, the Jefferson Memorial, the Lincoln Memorial, and the Federal Triangle buildings.
Reduced visibility has devalued what was once an exciting outdoor experience for an estimated 280 million annual park visitors. In the East, where the visual range used to be 90 miles, it’s now only 15 to 25 miles. The visibility in western states has declined from 140 miles to 35 to 90 miles.
Pollution can also cause problems with visibility, creating transportation hazards on the ground as well as increased collision dangers for aircraft. Haze in the atmosphere is created by tiny particles of pollution in the air that can either absorb light or scatter it before it reaches an observer. Once-clear vistas in our national parks are now shrouded in brown or white haze for much of the year.
One of the worst air pollution disasters occurred in 1948 in the town of Donora, Pennsylvania, which lies in the Monongahela River valley. The town’s location isn’t normally a problem, except on rare occasions when a temperature inversion forms. As warm air rises, it usually carries particles of pollution up into the atmosphere where they’re dispersed by wind. But during an inversion, a warm layer of air forms over a cooler, denser layer, trapping pollution near the ground.
That’s what happened in Donora in October 1948. The city of 14,000 was a company town, dominated by the US Steel factory where many of its residents worked. Townspeople were used to a certain level of smog, but on that fateful Thursday morning, residents awoke to a thick gray fog that seeped into homes even with the doors and windows closed. One by one, community members began to succumb to the acrid cloud, filling hospital emergency rooms with choking, wheezing victims. Many attempted to evacuate the city by car, but the dense smog and massive traffic jams soon made driving impossible. By Saturday, the town’s three funeral homes had no more room for bodies and a temporary morgue was set up. The deadly haze enshrouded Donora for the better part of five days until a rainstorm finally dispersed it.
When the air cleared, twenty people were dead and nearly 6,000 were ill from the smog’s effects. Many blamed the steel and zinc works along the river, which had continued to pump fumes into the saturated atmosphere until four days after the emergency began. The disaster led to the first air pollution conference, convened by President Harry Truman in 1950, which raised public awareness of the problem and set the stage for the Air Pollution Control Act, which was passed in 1956. For the first time, the US government identified air pollution as a national problem and announced its intention to improve the situation.