Acid Rain Essay, Research Paper

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.