Acid Rain Essay, Research Paper

Introduction: What Causes Acid Rain?

One of the main causes of acid rain is sulfur dioxide. Natural sources, which emit this gas, are

Volcanoes, sea spray, rotting vegetation and plankton. However, the burning of fossil fuels, such as

Coal and oil, are largely to be blamed for approximately half of the emissions of this gas in the world.

When sulfur dioxide reaches the atmosphere, it oxidizes to first form a sulfate ion. It then

Becomes sulfuric acid as it joins with hydrogen atoms in the air and falls back down to earth.

Oxidation occurs the most in clouds and especially in heavily polluted air where other compounds

such as ammonia and ozone help to catalyze the reaction, changing more sulfur dioxide to

sulfuric acid. However, not all of the sulphur dioxide is changed to sulfuric acid. In fact, a

substantial amount can float up into the atmosphere, move over to another area and return to earth

unconverted.

In the following pages I will show the effects of acid rain on:

? Effect on Trees and Soils

? Effect on Lakes and Aquatic Systems

? Effect on Materials

? Effect on Atmosphere

? Effect on Architecture

? Effect on Humans

Effect on Trees and Soils

One of the most serious impacts of acid precipitation is on forests and soils. Great damage is done

when sulfuric acid falls onto the earth as rain. Nutrients present in the soils are washed away.

Aluminium also present in the soil is freed and the roots of trees can absorb this toxic element.

Thus, the trees are starved to death as they are deprived of their vital nutrients such as calcium

and magnesium. Not all of the sulphur dioxide is converted to sulfuric acid. In fact, a substantial

amount can float into the atmosphere, move over to another area and return to the soils unconverted.

As this gas returns back to earth, it clogs up the stomata in the leaves, thus hindering photosynthesis.

Research has been made where red spruce seedlings were sprayed with different combinations of

sulfuric and nitric acid of pH ranging from 2.5 to 4.5. The needles of these seedlings were

observed to develop brown lesions. Eventually, the needles fall off. It was also found that new

needles grew more slowly at higher concentrations of acid used. Because the rate at which the

needles were falling was greater than the rate at which they were replenished, photosynthesis was

greatly affected, The actual way in which these needles were killed is still not yet known. However,

studies have shown that calcium and magnesium nutrients are washed away from their binding sites

when sulfuric acid enters the system. They are replaced by useless hydrogen atoms and this inhibits

photosynthesis.

Effect on Lakes and Aquatic Systems

One of the direct effects of acid rain is on lakes and its aquatic ecosystems. There are several routes

through which acidic chemicals can enter the lakes. Some chemical substances exist as dry particles

in the air while others enter the lakes as wet particles such as rain, snow, sleet, hail, dew or fog.

In addition, lakes can almost be thought of as the “sinks” of the earth, where rain that falls on land is

drained through the sewage systems eventually make their way into the lakes. Acid rain that falls

onto the earth washes off the nutrients out of the soil and carries toxic metals that have been released

from the soil into the lakes. Another harmful way in which acids can enter the lakes is spring acid

shock. When snow melts in spring rapidly due to a sudden temperature change, the acids and

chemicals in the snow are released into the soils. The melted snow then runs off to streams and

rivers, and gradually make their way into the lakes. The introduction of these acids and chemicals

into the lakes causes a sudden drastic change in the pH of the lakes – hence the term “spring acid

shock”. The aquatic ecosystem has no time to adjust to the sudden change.

In addition, springtime is an especially vulnerable time for many aquatic species since this is the time for

reproduction for amphibians, fish and insects. Many of these species lay their eggs in the water to hatch.

The sudden pH change is dangerous because the acids can cause serious deformities in their young or even

annihilate the whole species since the young of many of such species spend a significant part of their

life cycle in the water. Subsequently, sulfuric acid in water can affect the fish in the lakes in two ways:

directly and indirectly. Sulfuric acid (H2SO4) directly interferes with the fish’s ability to take in oxygen,

salt and nutrients needed to stay alive. For freshwater fish, maintaining osmoregulation is key in their

survival. Osmoregulation is the process of maintaining the delicate balance of salts and minerals in their

tissues. Acid molecules in the water cause mucus to form in their gills and this prevents the fish to absorb

oxygen as well. If the buildup of mucus increases, the fish would suffocate. In addition, a low pH will

throw off the balance of salts in the fish tissue. Salts levels such as the calcium (Ca+2) levels of some fish

cannot be maintained due to pH change. This results in poor reproduction – their eggs produced would be

damaged; they are either too brittle or too weak. Decreased Ca+2 levels also result in weak spines and

deformities. For example, crayfish need Ca+2 to maintain a healthy exoskeleton; low Ca+2 levels would

mean a weak exoskeleton. Another type of salt N+ also influences the well-being of the fish. As nitrogen-

containing fertilizers are washed off into the lakes, the nitrogen stimulates the growth of algae, which

logically would mean and increase in oxygen production, thus benefitting the fish. However, because of

increased deaths in the fish population due to acid rain, the decomposition process uses up a lot of the

oxygen, which leaves less for the surviving fish to take in. Indirectly, sulfuric acid releases heavy metals

present in soils to be dissociated and released. For example, Aluminium (Al+2) is harmless as part of a

compound, but because acid rain causes Al+2 to be released into the soils and gradually into the lakes, it

becomes lethal to the health of the fish in the lakes. Al+2 burns the gills of the fish and accumulates in their

organs, causing much damage. So, although many fish may be able to tolerate a pH of approximately 5.9,

this acid level is high enough to release Al+2 from the soils to kill the fish. This effect is further augmented

by spring acid shock. The effect of acid rain can be dynamically illustrated in a study done on Lake 223,

which started in 1976. Scientists monitored the pH and aquatic ecosystem of Lake 223. They observed that

as the pH of the Lake Decrease over the years, a number of crustaceans died out because of problems in

reproduction due to the acidity of the lake caused by acid precipitation.

At a pH of 5.6, algae growth in the lake was hindered and some types of small died out. Eventually, it was

followed by larger fish dying out with the same problem in reproduction; there were more adult fish in the

lake than there were young fish. Finally, in 1983, the lake reached a pH of 5 and the surviving fish in the

lake was thin and deformed and unable to reproduce. This case study obviously illustrates the significant

effect of acid rain on lakes and its aquatic ecosystem.

Effect on Materials

Acid rain also damages materials such as fabrics. For example, flags that are put up are being “eaten

away” by the acidic chemicals in the precipitation. Books and age-old art that are centuries old are

also being affected; the ventilation systems of the libraries and museums that hold them do not

prevent the acidic particles from entering the buildings and so, they get in and circulate within the

building, affecting and deteriorating the materials.

Effect on Atmosphere

Some of the constituents of acid pollution are sulphates, nitrates, hydrocarbons and ozone.

These exists as dry particles in the air and contribute to haze, affecting visibility.

This makes navigation especially hard for air pilots. Acid haze also interferes with the flow of sunlight

from the sun to the earth and back. In the Arctic, this affects the growth of lichens which in turn, affect the

caribou and reindeer which feed on it.

Effect on Architecture

Acid particles are also deposited on to buildings and statues, causing corrosion. For example, the

Capitol building in Ottawa has been disintegrating because of excess sulphur dioxide in the

atmosphere. Limestone and marble turn to a crumbling substance called gypsum upon contact with

the acid, which explains the corrosion of buildings and statues. In addition, bridges are corroding at a faster

rate, and the railway industry as well as the airplane industry have to expend more money in repairing the

Corrosive damage done by acid rain.

Not only is this an economically taxing problem caused by acid rain, but also a safety hazard to the

General public; as an illustration, in 1967, the bridge over the Ohio River collapsed killing 46 people – the

reason? Corrosion due to acid rain.

Effects On Humans

Among one of the serious side effects of acid pollution on humans is respiratory problems. The SO2

and NO2 emmisions give rise to respiratory problems such as asthma, dry coughs, headaches, eye,

nose and throat irritations. An indirect effect of acid precipitation on humans is that the toxic metals

dissolved in the water are absorbed in fruits, vegetables and in the tissues of animals. Although these

toxic metals do not directly affect the animals, they have serious effects on humans when they are

being consumed. For example, mercury that accumulate in the organs and tissues of the animals has

been linked with brain damage in children as well as nerve disorders, brain damage and death.

Similarly, another metal, Aluminium, present in the organs of the animals, has been associated with

kidney problems and recently, was suspected to be related to Alzheimer’s disease.

Elliott, Thomas C., and Robert G. Schwieger (Editors). The Acid Rain

Sourcebook. New York: McGraw-Hill, Inc., 1984.

Bown, William. “Europe’s forests fall to acid rain”. New Scientist. Vol. 127.

August 11, 1990. p. 17

Calvert, Jack G.(Editor) “SO2, NO and NO2 Oxidation Mechanisms:

Atmospheric Considerations” Acid Rain Precipitation Series, Volume 3. Toronto:

Butterworth Publishers, 1984.