Acid Rain

There are many environmental issues plaguing our world today. Among them are global warming and the depletion of the ozone layer. One problem that many people have not thought about too much in recent years is acid rain. Acid rain was thought of as a problem of the 1980s. Many people believe that it is a problem that has been solved. However, this is not the case. Acid rain is still a problem in the year 2001. There are measures to control acid rain, yet the earth still needs more time to recover from acid rain’s harsh effects.

Acid rain is a sweeping term, which includes not only acidic rain but snow, sleet, fog and other forms of precipitation, as well as dry deposition of acidic compounds (EPA). Acid rain is formed by the combination of sulfur and nitrogen oxides and water that is found in the atmosphere. At high temperatures, nitrogen and oxygen in the atmosphere can combine to form nitric oxide.

N_{2 (g)} + O_{2 (g)} ® 2NO _(g)

This reaction can take place in internal combustion engines of automobiles and in electrical power plants. Nitric oxide then reacts with the oxygen in the atmosphere to form nitrogen dioxide.

2NO _(g) + O_{2 (g)} ® 2NO_{2 (g)}

The nitrogen dioxide can further react with water in the atmosphere to form both nitric acid and nitric oxide.

3NO_{2 (g)} + 3H₂O _(g) ® 2H₃O⁺ _(aq) + 2NO₃^- _(aq) +NO _(g)

Another compound that is involved with the formation of acid rain is sulfur dioxide. Sulfur dioxide is a by-product, which is formed by burning fossil fuels. It reacts with water to form sulfurous acid.

SO_{2 (g)} + H₂O _(l) ® H₂SO_{3 (aq)}

The sulfur dioxide can also further oxidizes in the atmosphere and form sulfur trioxide. This then reacts with water to produce sulfuric acid.

2SO_{2 (g)} + O_{2 (g)} ® 2SO_{3 (g)}

SO_{3 (g)} + 2H₂O _(l) ® H₃O⁺ _(aq) + HSO₄^- _(aq)

These acids are the major components of acid rain (Jenkins, Atkins 690).

Acid rain is harmful to the environment in many ways. It kills plants and fish, it ruins soil and water, and it even damages cars and buildings. How exactly does acid rain do so much damage? Lakes contain substances such as magnesium and calcium, which act as buffers. A buffer is a substance, which resists a change in pH. The problem with acid rain is there is too much acid, so the buffers exceed their buffering capacities (Roberts 70). Most lakes have a pH between 6 and 8 (7 being neutral). Because of acid rain, some lakes have a pH of 5 or less, and Little Echo Pond in Franklin, New York, has the lowest recorded acidity of 4.2. At such low pH levels, fish and other aquatic life die (EPA). The chart below shows which aquatic organisms can live in certain pH levels (http://www.epa.gov/airmarkets/acidrain/effects/surfacewater.html).

Soil works in a similar fashion to that of the bodies of water. Soils also contain chemicals, which act as buffers. The buffering capacity of the soil depends on both the thickness of the soil and the bedrock beneath it. Soils in the southeastern part of the United States have large buffering capacities, and soils in the Northeast have a lower capacity for acid rain (EPA). Acid rain dissolves base cations at a rate that is faster than the bedrock beneath the soil can replace them (Krajick 195). One of the ways acid rain destroys soil is by reacting with some of the substances that act as buffers. For example, sulfuric acid can react with calcium cations to form calcium sulfate. Since calcium sulfate is an insoluble substance, it cannot be reabsorbed by soil or used as a nutrient by plants (Jenkins, Atkins 691). This is one of the ways that acid rain kills trees and other plant life.

Another way acid rain kills plants is by reacting with the normally harmless aluminum in the soil. When aluminum is dissolved it is poisonous. Aluminum can also clog the roots of plants, which prevents them from getting any nutrients. Acid rain can also react with the calcium that is found in pine needles which ruins the membranes and leaves the trees weak. Acid rain does not directly kill trees and plants, however. Christopher Cronan, a biologist at the University of Maine, tells how “instead of killing directly, acid rain usually leaves trees susceptible to drought or insects, which finish the job” (Krajick 195). There are areas in Germany where large amounts of the Black Forest have been completely destroyed by acid rain.

Acid rain also takes its toll on people. Acid rain does not seem to directly affect humans because we can walk around in it and swim in acidic lakes without a problem. The dry deposition of toxic chemicals, however, can be breathed in. That can cause problems such as asthma and bronchitis (EPA). The aluminum dissolved in water is just as poisonous to humans as it is to plants. Other metals such as copper and lead can also be dissolved in acid rain and seep into drinking water. In Sweden, there are some areas where the copper levels are so high, they turn hair green. These high copper levels also cause liver and kidney damage (Miller 91). Acid rain can permanently damage the paint on cars leaving areas that looked as if they had been etched (EPA). Statues, sculptures and buildings are also primary targets for acid rain.

Acid rain does not stay in one place. That poses a problem between neighboring countries. Sulfur and nitrogen oxides can be easily carried miles by the wind, and then fall to the earth as acid rain. Scandinavian countries took an early start in reducing their sulfur emissions. Unfortunately, pollution from central Europe has deposited itself via acid rain on Scandinavian soil

How acid rain is moved by wind. Geographical v72 no5 May 2000, p.90

(Stoddard et al 857). As much as 50% of the acid rain in Canada was caused by American air pollution (Miller 91). Acid rain is not just spreading by air. The problem has spread to the southwestern part of the United States because more people are living there and driving vehicles. Plus, there are large herds of cattle. Both of these sources produce nitrogen oxides (Krajick 196).

The government has taken large amounts of time and money to study and control acid rain. Since the 1980s, Congress has spent over half a billion dollar on a ten year research project to study acid rain (Roberts 70). The Clean Air Act was started by Congress in 1990 to reduce the sulfur dioxide emissions by 10 million tons and the nitrogen oxide emissions by 2 million tons (See http://www.epa.gov/airmarkets/arp/overview.html for more information). Since 1973, the United States’ emissions of sulfur dioxide have been reduced by 40% from 28.8 metric tons per year. By 2010 the amount of sulfur dioxide emissions are expected to be down from the amount produced in the 1970s by 50%. However, some scientists do not think that this is enough. Ten top acid rain researchers said that sulfur dioxide emissions would have to be reduced by another 80% to repair all the damage done to lakes and trees by 2010. Plus, nitrogen oxides would have to be more strictly regulated (Krajick 195).

Although some lakes, streams, and forests are showing improvement, many are not. According to a group of scientists monitoring acid rain, “No significant decrease in nitrogen deposition or nitrate concentrations in streams can be expected in the near future in either North America or Europe” (Stoddard et al 856). These same scientists report that in parts of Germany streams show a continually low pH (857). There are some lakes in the northeastern and Midwestern part of the United States that are still acidic, and they look like they will not recover for decades (Roberts 70). It is not just water that is affected. Soils in the Southeast, which can absorb large amounts of acid rain, may take hundreds of years to recover (Krajick 196). Unfortunately, the recovery process is taking a lot longer than scientists had originally suspected.

As the government put a lot of effort into controlling and reducing acid rain, we too must help. Simply walking short distances instead of driving and turning of the lights when not in the room are ways to reduce pollutants that cause acid rain. Find out what the Environmental Protection Agency suggests at http://www.epa.gov/airmarkets/acidrain/society/index.html.

Although many may see acid rain as a problem that is being controlled, it is a problem that should not be ignored. There may be bigger environmental issues plaguing our earth, but acid rain continues be a problem.

Bibliography

Jones, Loretta, and Atkins, Peter. Chemistry: Molecules, Matter, and Change—

4^th Ed. New York: W.H. Freeman and Company, 2000.

Environmental Protection Agency homepage and links

http://www.epa.gov/airmarkets/acidrain/index.html

Krajick, Kevin. “Long-Term Data Show Lingering Effects From Acid Rain.” Science

292 (2001): 195-196.

Miller, Norman. “Rains of Terror.” Geographical 72.5 (2000): 90-91

Roberts, Leslie. “Acid Rain: Forgotten, Not Gone.” U.S. News & World Report 1

Nov. 1999: 70.

Stoddard, J.L., et al. “Is Acidification Still an Ecological Threat.” Nature 407

(2000): 856-857.