Acid Deposition - Causes, Effects, And Resolutions

Acid deposition is a growing danger with industry booming throughout the world. What acid deposition is, its many forms, including why it occurs, how it affects the earth, and methods that are used to try to minimize the damage.

Acid deposition is any combination of airborne dry acidic particles and precipitation that falls to the earth. It occurs in forms such as rain, snow, mist, and fog. With industry booming throughout the world, acid deposition is a growing danger. Its impact on aquatic areas, forests and all life forms is unhealthy and destructive. Some solutions are implemented effectively today, but most acid deposition can not be remedied.

Two of the main sources of acid deposition are natural emissions and anthropogenic. Natural causes include volcano emissions, lightning, and microbial processes, while anthropogenic refers to industrial emissions and other man-made polluters. When nitric and sulfuric acids are released into the atmosphere by smokestacks, fuel combustion, or natural causes, they mix with water vapor at unusual proportions to cause acid deposition. Although both humans and nature cause this corrosive precipitation, anthropogenic sources release approximately twice as much airborne acid. Since humans are responsible for two-thirds of this pollution, it appears to follow that humans should be able to minimize it. Unfortunately, as will be discussed later, the solutions are limited in themselves.

The effects of anthropogenic acid deposition are evident in and around industrialized regions of the world. In the United States, there is a high concentration of acid deposition mainly in the northeast. In the surrounding eastern half of the country the pH level is also below normal (indicating acidity). The problems associated with anthropogenic as well as naturally occurring acid deposition occur in aquatic environments, forests and human environments.

In water, acid deposition mutates and kills fish. There are a few ways that this happens. First, the acid that is directly deposited into bodies of water kills some marine life. Second, the acids can leach heavy metals in the water and release harmful metals into the aquatic environment. After plants and animals absorb these metals, they die, become sterile, or produce mutated offspring. Ultimately, entire lakes and rivers become lifeless due to the effects of acid deposition. Even fish that survive in areas such as the eastern United States are generally highly toxic to eat because of the mercury they harbor.

The impact of acid deposition of forests is most crucial in the soil. At first, acid deposition actually improves soil condition by supplying essential chemicals for soil nutrition. However, over time these chemicals become too potent and leach the buffering agents in the soil. These buffering agents, such as calcium and magnesium salts, are essential to protecting the forest life from the harmful effects of acid deposition. Once they are removed, aluminum ions are dissolved from minerals and released into the soil environment. The combination of the toxic aluminum and disappearing calcium results in stunted tree growth. Either forests die off or new acid-tolerant species gradually replace the previous ones.

As for the direct effects on humans, acid deposition is not quite as serious. Mainly artifacts are destroyed by acid deposition. Limestone (or marble) is extremely vulnerable to corrosion from acid; thus, monuments and statues are now crumbling due to acid deposition.

A more serious infliction caused by acid deposition, however, is the secondary effect of polluted water, dying forests, and airborne chemicals. Animals that eat fish that are toxic with mercury suffer serious repercussions such as neurological disorders and even death. A decrease in the number of trees leads to less oxygen and more carbon dioxide in the air, causing imbalance. Airborne chemicals are unhealthy to creatures with lungs, which are not intended to filter such large amounts of toxins.

It is anticipated that a fifty percent reduction in the amount of acid-causing emissions would preserve the environment's equilibrium well enough. However, this type of result is difficult to achieve. Six main strategies to accomplish this goal have been proposed. 

They are: 

1) coal washing (to remove sulfur before burning, 

2) fluidized bed combustion,

3) fuel switching (for burning), 

4) scrubbers (in smokestacks),

5) alternative power plants, and 

6) reductions in the consumption of energy.

Some of these methods are viable and worthwhile, but they all have disadvantages and none is a perfect solution. The first two create a byproduct of polluted water, fuel switching is expensive, scrubbers are highly effective but they are not required in older plants that were "grandfathered" in before recent environmental laws, and the last two approaches require large shifts in the energy policy of the United States. Much is being done to reduce the amount of damage incurred by acid deposition, but new solutions must constantly be devised in order to solve the problem.