Part I – What is Acid Rain? Acid rain is a general term that refers to the deposition of acidic materials from the atmosphere on the surface of the earth. Therefore it is more appropriately called acid deposition. There are two types of acid deposition, wet deposition and dry deposition. Wet deposition, or acid precipitation, refers to acidic rain, snow, hail or sleet. It occurs when pollutants such as Sulphur and Nitrogen oxides (SOx, NOx) are present in the atmosphere and react with water vapor to form acidic solutions such as Sulphurous Acid (H2SO3), Sulphuric Acid (H2SO4), Nitrous Acid (HNO2) and Nitric Acid (HNO3) that fall to Earth’s surface as precipitation. Dry deposition refers to the deposition of particles and gases of Sulphur and Nitrogen oxides (SOx, NOx) on Earth’s surface. These particles and gases become acids when they react with water on the surface of the Earth. Natural precipitation has a pH of about 5.6. It is slightly acidic due to dissolved Carbon dioxide (CO2). In comparison, acid deposition usually has a pH of about 4.3 – 5.0.
As stated above, acid deposition is caused by pollutants in the atmosphere. The majority of these pollutants are released in to the atmosphere by the burning of fossil fuels. Fuels such as coal and oil contain Sulphur and when they are burned they elease it. When Sulphur is released into the atmosphere by combustion it reacts accordingly:
S + O2 ƒ  SO2
Sulphur released by the burning of fuels such as oil and coal reacts with Oxygen in the air to yield Sulphur dioxide.
2SO2 + O2 ‘ 2SO3
Sulphur dioxide reacts with the Oxygen in the air to yield Sulphur trioxide
SO2 + H2O ƒ  H2SO3
SO3 + H2O ƒ  H2SO4
Sulphur dioxide and Sulphur trioxide react with water, either in the atmosphere or on the surface of the Earth, to yield Sulphurous Acid and Sulphuric Acid
Combustion of fuels in cars releases another pollutant, Nitrogen gas. Once Nitrogen gas is released in to the atmosphere by combustion it reacts accordingly:
N2 + O2 ƒ  2NO
N2 + 2O2 ƒ  2NO2
Nitrogen gas reacts with Oxygen in the air to yield Nitric oxide and Nitrogen dioxide
2NO + O2 ‘ 2NO2
Nitric oxide reacts with oxygen in the air to yield Nitrogen dioxide
2NO2 + H2O ƒ  HNO2 + HNO3
Nitrogen dioxide reacts with water, either in the atmosphere or on the surface of the Earth, to yield Nitrous Acid and Nitric Acid.
Small amounts of these pollutants are also released into the atmosphere naturally. Decomposing vegetation releases gases that contribute to pollutants in the atmosphere. Lightning produces Nitric oxide (NO) and volcanic eruptions release Sulphur dioxide (SO2).
Some atmospheric chemists such as Dr. Ronald Prinn believe that acid rain has been around for millions of years. Dr. Prinn believes that acid rain could be responsible for the extinction of dinosaurs. However, the first known observation of acid rain did not take place until the 19th century, around the time of the Industrial Revolution. It was Robert Angus Smith, an English scientist, who came up with the term “acid rain” in 1872 when he observed that acidic precipitation was damaging plants. Acid rain was not considered a major environmental concern until the 1970’s when scientists observed the effects of acid rain on ecosystems. When it was made clear that acid rain has negative impacts on ecosystems and that it is not only a regional issue but rather an international one, governments began to get involved. In 1991, Canada and the United States signed the Canada-US Air Quality Agreement and committed to reduce SOx and NOx emissions.
Part II – How does Acid Rain affect our Society?
Acid rain has an extremely negative impact on our society. The most devastating consequence of acid rain is the affect that it has on terrestial as well as aquatic ecosystems. In terrestrial ecosystems, acid rain destroys plants. Acid rain causes toxic metals such as aluminum, copper, lead, manganese and zinc to leach out of rocks and soils. Additionally, nutrients present in topsoil leach down to the subsoil. Plant growth is significantly decreased in soils lacking nutrients and rich in poisonous alumnium. The other toxic metals released by acidic soil kill earthworms and nitrogen-fixing bacteria, both of which are essential to plant growth. Acid rain can also wears away the protective coating of leaves. These consequences also have an effect on the agriculture industry. Many crops cannot grow in soils that are lacking nutrients and contain aluminum. Furthermore, acid rain destroys many food crops such as radishes, tomatoes and apples. The effects of acid rain extends to aquatic ecosystems. The toxic substances that are leached out of rocks and soil can be washed in to lakes and rivers. Fish are easily poisoned by these toxic substances. The acidic environment that acid rain creates in lakes and rivers is also harmful to fish and other aquatic organisms. The acidity kills many organisms that are usually at the bottom of a complex aquatic food chain. The food chain then collapses and the populations of many organisms significantly decrease. Acid rain also interrupts fish reproduction as it can destroy fish eggs.

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There are many more negative effects of acid rain. Fresh water supply can be contaminated by the acidity as well as by the metals that are leached from rocks and soil due to acid rain. Acid rain can also corrode water transportation pipes, allowing metal to enter the water supply. Another consequence of acid rain is the effect that it has on a cityscape. Acid rain can significantly damage metal and stone structures. Finally, acid rain can have an affect on human health. Contaminated water can cause health concerns. The SOx and NOx in dry deposition can cause numerous respiratory diseases such as asthma, emphysema and bronchitis. Furthermore, Nitrogen oxides (NOx) can react with volatile organic compounds in the air near the surface of the Earth to yield Ozone, which can be very detrimental to the respiratory system.
Part III – What should we do about Acid Rain?
There are two methods that can be taken when approaching the issue of acid rain. We can either ignore the issue or we can do something about it and attempt to control the problem. Both methods have their advantages and disadvantages. If we ignore acid rain, nothing will be done to control or stop it and we will continue to suffer from its consequences. The advantage of this method is that no resources have to be expended. Governments, industries and citizens do not have to invest any money in to attempting to solve the problem. Governments do not have to invest in new energy sources. Industries can go on using current techniques without having to invest in new strategies in order to assist in solving the problem. Citizens can also go on without trying to conserve resources in order to attempt to stop acid rain. However, the disadvantage of this method is that acid rain will remain a threat to terrestrial ecosystems, aquatic ecosystems, the agriculture industry, cityscapes, fresh water supplies and human health. If acid rain continues the effects could be devastating. The second method is to do something about the problem and attempt to control acid rain. In order to do so pollutant emissions must be reduced, alternative sources of energy must be found and used, resources must be conserved, polices must be put in place in order to protect air quality and lakes and rivers must be neutralized. The advantage to this method is that it has the potential to control or even stop acid rain. By doing so we can save many terrestrial and aquatic ecosystems, increase yield of crops, prevent damage to cityscapes, keep supplies of fresh water clean and eliminate any risk of human health being put at risk due to acid rain. However, the disadvantage to this method is that it is very expensive. It also requires governments, industries and citizens to take action. To reduce pollutant emissions, companies have to invest in new cleaner technology. Such technology includes Sulphur scrubbers in factories and catalytic converters in cars. These technologies are expensive and require a large investment from industries. Furthermore, if policies are put in place in order to maintain air quality, many companies will have to invest in new technology in order to meet these new regulations. In order to find and use new energy sources industries as well as governments will have to invest a large amount of money into research and implementation. Additionally, neutralizing lakes and rivers that have been damaged by acid rain with limestone will also require the government to spend a large amount of money. All of these costs will eventually be passed down to the consumer as well as the citizen. In order to control acid rain we must also conserve our natural resources. This will be very hard for a society that is driven by exploitation. Revenues of many companies might go down if consumers begin to conserve. Revenues also may go down if companies begin consider the environment before they consider profit. After examining the advantages and disadvantages of ignoring the situation and controlling the situation, I think that we must control it. It would be wrong to ignore acid rain and the advantages of controlling it really outweigh its disadvantages. Controlling and trying to eliminate acid rain will be expensive and require governments, industries and citizens to take action but it is the right thing to do. We must save our ecosystems, our crops, our cities, our water and our health from the detrimental effects of acid rain.