Acid rain is rain that is more acidic than normal. Acid rain is a complicated problem. Primarily caused by air pollution, acid rain’s spread and damage involves weather, chemistry, soil, and the life cycles of plants and animals on the land and in lakes and streams. This form of air pollution is currently a subject of great controversy because of its worldwide environmental damages. For the last ten years, this problem has brought destruction to thousands of lakes and streams in the United States, Canada, and parts of Europe. Scientists have discovered that air pollution from the burning of fossil fuels is the major cause of acid rain. Power plants and factories burn coal and oil. Power plants use that coal and oil to produce the electricity for our homes and to run our electric appliances. We also burn natural gas, coal, and oil to heat our homes. The smoke and fumes from burning fossil fuels rise into the atmosphere and combine with the moisture in the air to form acid rain. The main chemicals in air pollution that creates acid rain are sulfur dioxide and nitrogen oxides. Acid rain usually forms high in the clouds where sulfur dioxide and nitrogen oxides react with water, oxygen, and oxidants. This forms a mild solution of sulfuric acid and nitric acid.
Sunlight increases the rate of most of these reactions. Rainwater, snow, fog, and other forms of precipitation containing those mild solutions of sulfuric and nitric acids fall to the earth as acid rain. Water moves through every living plant and animal, streams, lakes, and oceans in the hydrologic cycle. In that cycle, water evaporates from the land and sea into the atmosphere. Water in the atmosphere then condenses to form clouds. Clouds release the water back to the earth as rain, snow, or fog. When water droplets fall to the earth they pick up particles and chemicals that float in the air. Even clean, unpolluted air has some particles such as dust or pollen. Clean air also contains naturally occurring gases such as carbon dioxide. The interaction between the water droplets and the carbon dioxide in the atmosphere, and also from chlorine, which comes from the salt in the sea, gives rain an average pH of about 5.6. This can make even clean rain slightly acidic.
Other natural sources of acids and bases in the atmosphere may lower or raise the pH in clean rain water. But when rain contains pollutants, especially sulfur dioxide and nitrogen oxides, the rain water can become very acidic. Acid rain does not account for all of the acidity that falls back to earth from pollutants. About half the acidity in the atmosphere comes back to the earth as gases and dry particles. The wind blows these acidic particles and gases onto buildings, cars, homes and trees. Sometimes these gases and particles can eat away the things on which they settle. Dry deposited gases and particles are sometimes washed from trees and other surfaces by rainstorms. When that happens, the acids get into the runoff and adds to the acids already present, making the combination more acidic than the falling rain alone. This mixing process is called acid deposition.
The chemical reactions that change air pollution to acid rain can take from several hours to several days. Years ago, when smokestacks were only a few stories high, pollution from smokestacks usually stayed near the ground and settled on land nearby. This caused unhealthy conditions for plants and animals near the smokestacks. To reduce this pollution, the government passed a law permitting the construction of very tall smokestacks. At that time, people thought that if the pollution were sent high into the air it would no longer be a problem. Scientists now know that this is incorrect. Sending pollution high into the sky increases the time that the pollution stays in the air. The longer the pollution is in the air, the greater are the chances that the pollutants will form acid rain. In addition, the wind can carry these pollutants for hundreds of miles before they become joined with water droplets to form acid rain. For that reason, acid rain can also be a problem in areas far from the polluting smokestacks.
Dry deposition is usually greater near cities and industrial areas where the pollutants are frequently sent into the atmosphere. The large amounts of acids produced by human activities overload the earths natural acidity such as hot springs and volcanoes. In iron and steel production, the melting of metal sulfate ore produces pure metal. This causes the release of sulfur dioxide. Metals such as zinc, nickel, and copper are commonly obtained by this process. The other chemical that is also chiefly responsible for the make-up of acid rain is nitrogen oxide. Oxides of nitrogen is a term used to describe any compound of nitrogen with any amount of oxygen atoms. Nitrogen monoxide and nitrogen dioxide are all oxides of nitrogen. These gases are by-products of firing processes of extreme high temperatures (automobiles, utility plants), and in chemical industries (fertilizer production). Transportation makes up 43%, and 32% belongs to industrial combustion.
Nitrogen oxide is a dangerous gas by itself. As mentioned before, any precipitation with a pH level less than 5.6 are considered to be acid rain. The difference between regular precipitation and acid precipitation is the pH level. A pH scale is used to determine if a specific solution is acidic or basic. Any number below seven is considered to be acidic. Any number above seven is considered to be basic. Most pH scales use a range from zero to fourteen. Seven is the neutral point (pure water). A pH from about 6.5 to 8.0 is considered the safe zone. Between these numbers, organisms are in very little or no harm. Sulfur dioxide oxidation is most common in clouds, especially in heavily polluted air, which has compounds such as ammonia and ozone. Not all sulfur dioxide in the atmosphere is converted to sulfuric acid. A substantial amount can float up into the atmosphere and be transported to another area and return to earth as sulfur dioxide.
Like sulfur dioxide, nitrogen oxides use much the same type of process. These reactions are speeded up in heavily polluted clouds where traces of iron, manganese, ammonia, and hydrogen peroxide are present. Nitrogen oxides mainly come from automobile exhaust. In the atmosphere it reacts with water to form nitric or nitrous acid. Over the years, scientists have noticed that some forests have been growing more and more slowly for no apparent reason. Trees do not grow as fast as they did before. Leaves and pines needles turn brown and fall off when they are supposed to be green. Eventually, after several years of collecting and recording information on the chemistry and biology of the forest, researchers have concluded that this was the work of acid rain. During fall, rain washes the leaves of the branches and they fall to the forest floor. Some of the water is absorbed into the soil. Water run-off enters nearby streams, rivers, or lakes.
The soil may have neutralized some or all of the acidity from the acid in the rainwater. This natural neutralization is called buffering capacity. Without buffering capacity, soil pH would change rapidly. Midwestern states like Nebraska and Indiana have soil that is well buffered. Mountainous northeast areas such as the Adirondack Mountains are less able to buffer acid. High pH levels in the soil cause soil weathering and removes nutrients. It can also make some toxic elements, for example aluminum, more soluble. Acid rain does not kill trees immediately or directly. Instead, it weakens trees by destroying its leaves and limiting the nutrients available to it. Acid rain can seep into the ground, poisoning the trees with toxic substances that are slowly absorbed through the roots. Acid rain also dissolves or washes away some nutrients and minerals that help trees grow. Not only does acid rain strip away the nutrients from the plants, they help release toxic substance such as aluminum into the soil. When acid rain is frequent, leaves tend to lose their protective waxy coating.
When leaves lose their coating, the plant itself is open to disease. When the leaves are damaged, the plant can not produce enough food energy for it to remain healthy. Acid rain also effects organisms in aquatic biomes. Most lakes and streams have a pH level between six and eight. Some lakes are naturally acidic even without the effects of acid rain. There are several routes through which acid rain can enter the lakes. Some chemical substances exist as dry particles in the atmosphere, while others enter directly into the lake by rain or snow. Acid rain that has fallen on land can be drained through sewage systems leading to lakes. Acids can also enter lakes when acid snow melts in the spring, the acids in the snow either wash into streams or seeps into the ground. Spring is a vulnerable time for many species since this is the time for reproduction. The sudden change in pH level is dangerous because the acid can cause serious deformities in their young. Generally, the young of most species are more sensitive to a pH change then older animals of the same species.
Not all species can tolerate the same amount of acid. For example, frogs may tolerate relatively high levels of acidity, while snails are more sensitive to pH changes. Acid molecules can cause mucus to form in the gills of fish, preventing the fish from absorbing oxygen easily. Also, a low pH level will throw off the balance of salt in the fish’s tissue. Sometimes pH changes can cause a problem in reproduction as fish eggs can become too brittle and break. Sometimes when acid rainfall runs off the land, it carries fertilizers with it. Fertilizer helps stimulate the growth of algae because of the amount of nitrogen in it. That makes matters worse because due to the increase in the death of fish their decomposition takes up even more oxygen. This takes away oxygen from surviving fish. In other terms, acid rain doesnt help aquatic ecosystems in any way. Acid rain does not only damage the natural ecosystems, but also man-made materials and structures. Marble, limestone, and sandstone can easily be dissolved by acid rain. Metals, paints, cloth, and ceramic can easily be corroded.
Man-made materials slowly deteriorate even when exposed to unpolluted rain, but acid rain speeds up the process. Acid rain also causes carvings, monuments, and statues carved in stones to lose their features. The repairs on buildings and monuments can be quite costly. In 1990, the United States spent $35 billion on paint damage. In 1985, the Cologne Cathedral cost the Germans approximately $20 million in repairs. The Roman monuments cost the Romans about $200 million for acid rain repairs. Another famous monument effected by acid rain is the Spynx in Egypt. This guys nose is pretty much gone. Most importantly, acid rain affects the health of human beings. It can harm us through the atmosphere or through the soil from which our food is grown. Acid rain causes toxic metals to break loose from their natural chemical compounds. Toxic metals themselves are dangerous, but when combined with other elements are harmless. Toxic metals might be absorbed by the drinking water, crops, or animals that a human may eat such as pig, deer or cow.
These foods that are consumed could cause nerve damage to children, severe brain damage or even death. Scientists believe that aluminum is somehow related to Alzheimer’s disease. Acid rain also causes respiratory problems that can even lead to death. The sulfur dioxide and nitrogen oxide emission gives risk to respiratory problems such as dry coughs, asthma, headaches, and eye, nose, and throat irritation. Polluted rainfall is especially harmful to those who already suffer from asthma or those who have a hard time breathing. Even healthy people can have their lungs damaged by acid air pollutants. In 1991, the United States and Canada signed an air quality agreement. Ever since that time, both countries have taken actions to reduce sulfur dioxide emission.
The United States agree to reduce their annual sulfur dioxide emission by about ten million tons by the year 2000. Since most nitrogen oxide emissions are from cars, catalytic converters must be installed to reduce this emission. The catalytic converter is placed on the exhaust pipe, making all exhaust pass though it. This converter looks like a dense honeycomb. This converts nitrogen oxides, carbon dioxides and unburned hydrocarbons into a cleaner state. Acid rain is an issue that can not be over looked. It has the potential to destroy anything it touches or interacts with it. When acid rain damages the forest or the environment it affects humans in the long run. Once forests are totally destroyed and lakes are totally polluted animal populations begin to decrease because of lack of food and shelter. If all the animals, which are our food source, die out, humans would die out to. Acid rain can also destroy our homes and monuments, which we hold dearly. What humans can do to reduce sulfur and nitrogen dioxide emission is to reduce their use of fossil fuels.
Car pools, public transportation, or walking can literally reduce tons of nitrogen oxide emissions. Using less energy benefits the environment because the energy used comes from fossil fuels which can lead to acid rain. An alternative power source can also be used in power plants and homes to reduce emissions. These alternatives are: geothermal energy, solar power, wind energy, and water energy. In conclusion, the two primary sources of acid rain are sulfur dioxide and nitrogen oxide. Automobiles are the main source of nitrogen oxide emissions, and utility factories are the main source for sulfur dioxide emissions. These gases evaporate into the atmosphere and then oxidized in clouds to form nitric or nitrous acid and sulfuric acid.
When these acids fall back to the earth they do not cause damage to just the environment but also to human health. Acid rain kills plant life and destroys life in lakes and ponds. The pollutants in acid rain cause problem in human respiratory systems. The pollutants attack humans indirectly through the foods they consume and can effect human health directly when humans inhale pollutants. Governments have passed laws to reduce emissions of sulfur dioxide and nitrogen oxide, but it is no use unless people start to work together in stopping the release of these pollutants. If the acid rain destroys our environment, eventually it will destroy us as well. Acid rain is poorly understood and we will probably spend billions of dollars on research and there will still be different opinions. There may be no clear answer to the acid rain problem.