Research in Acid Deposition

Acid deposition is a general name for a number of phenomena, namely acid rain, acid fog and acid mist. It occurs during the combustion of fossil fuels and other industrial processes undergo complex chemical reactions and emitted gases in the atmosphere. These gases it then emitted to the Earth as wet deposition or dry deposition. Acid deposition can cause harmful effect on the environment.

For wet deposition, it occurs when the acidic chemicals in the air blow by wing and transport to the areas where the weather is wet. Then, these acidic chemicals will fall to the ground in the form of rain, sleet, fog, snow or mist which is the type of wet deposition. This will cause the acid to be removed from atmosphere and deposit on the earth's surface. These acids are toxic and when they flow through the ground, most of the aquatic life, animals, and plants will be affected.

Besides that, for dry deposition, it occurs when the acidic chemicals in the air blow by wing and transport to the areas where the weather is dry. Almost50% of the acidic chemicals in the atmosphere fall back through dry deposition. Theses acidic chemicals slip into dust or smoke and fall to the ground as dry particles. They will stick to the buildings, cars, houses, and trees.

Acid deposition is usually caused by the accumulation of acids or acidic compounds on the Earth’s surface. The main chemical precursors are sulfur dioxide (SO2)and nitrogen oxides (NOx). When these two compounds react with water, oxygen, carbon dioxide, and sunlight in the atmosphere to form sulphuric acids (H2SO4) and nitric acids (HNO3) which is the primary agents of acid deposition.

More recently, acid precipitation or acid rain that is more acidic than normal has been linked to air pollution. Acid rain damage historic artworks, statues, and classic architecture and erodes names, dates and marking on cemetery gravestones. It also impairs the production of fish.

Emission of chemical gases such as sulfur dioxide (SO2) and nitrogen oxides (NOX) into the atmosphere is a major contributor to acid deposition. This mainly causes man-made sources. SO2 and NOX gases are emitted through human activities. These chemical gases can be released from factories, particularly in hear and power generation facilities, large industrial boilers, action of bacteria on fertilizers or vehicle exhaust.

Their gases are reactive and they will react with the water, oxygen or other chemicals substances in the atmosphere to form more acidic pollutants. This reaction can cause the formation of several acidic compounds like nitric acid, sulphuric acid, and ammonium nitrate. Acid deposition in this area should be very high.

On the other hand, a small number of chemical gases come from natural sources. For example, they can come from volcanic gases which contain sulfur dioxide. Most of these gases are come from the use of combustion of fossil fuels to generate electricity. Also, a natural source like lightning strikes can produce oxides of nitrogen that will react with the water to form acid rain.

SO2 and NOX can be blown by wind and transport over long distances to other areas. This results in the spreading of acid deposition and causes a negative impact on the environment, buildings and living things.

The burning of hydrocarbon fuels produces sulfur dioxide (SO2).

S+ O2  SO2

SO2+ H2O (rainwater) + O2 (Oxygen in air)  H2SO4(Acid Deposition)

Nitrogen and oxygen combine to make oxides of nitrogen.

N2+ 2O2  2NO2

H2O(rainwater) + O2 (Oxygen in air)  HNO3 (Acid Deposition)

Acid rain has many ecological effects, but none is greater than its impact on lakes, streams, wetlands, and other aquatic environments. Acid rain either falls directly on aquatic bodies or gets run off the forests, roads and fields to flow into streams, rivers and lakes make waters acidic, which lower the overall pH of the waterbody. The aquatic plants and animals need a particular pH level of about 4.8 to survive. If the pH level falls below that, the conditions become hostile for the survival of aquatic life.

Acid rain also damages forests, especially those at higher elevations. It robs the soil of essential nutrients and releases aluminum in the soil, which makes it hard for trees to take up water. It makes trees vulnerable to disease, extreme weather, and insects by destroying their leaves, damaging the bark and arresting their growth.

Moreover, acid rain can have destructive effects on many objects, including buildings, statues, monuments, and cars. The chemicals found in acid rain can cause paint to peel and stone statues to begin to appear old and worn down, which reduces their value and beauty.

For example, acid rain will eventually dissolve a marble statue. Acid rain often contains sulphuric acid, H2SO4, which will react with the calcium carbonate, CaCO3, to produce relatively insoluble calcium sulfate, CaSO4, carbon dioxide, CO2, and water, H2O.

CaCO3 (s) + H2SO4

(aq) CaSO4

(s) + CO2 (g) + H2O(l)

If large quantities of water are present, the calcium sulfate will be removed from the surface of the statue. In time, the quantities of calcium carbonate converted by acid rains into calcium sulfate, water, and carbon dioxide will become quite visible.

One of the most fundamental solutions is to utilize fuels that burn more cleanly or to burn coal more efficiently. This will greatly reduce the number of acids released into the atmosphere. Besides fossil fuels, there is a wide range of alternative energy sources that can generate electrical power. For example, wind energy, geothermal energy, solar energy, hydropower, and nuclear power. Fuel cells, natural gas, and batteries can also substitute use of fossil fuel as cleaner energy sources. As of today, all energy sources have environmental and economic costs as well as benefits. The only solution is using sustainable energy that can protect the future.

On the other hand, individuals can help to prevent acid rain by conserving energy. A small step can be taken by the individual by turning off the lights, computers, and other electrical appliances, when not in use. The fewer electricity people use in their homes, the fewer chemicals power plants will emit. While purchasing, individual can buy the appliances, which consume less energy. Vehicles are also major fossil fuel users, so drivers can reduce emissions by using public transportation, carpooling, biking, or simply walking wherever possible to nearby places instead of driving. This can help us save fuel and gas, as well as reduce the adverse effects.

Lastly, there are some things that people can do to repair the damage caused by acid rain to lakes and rivers. Limestone or lime can be added to acidic surface waters to balances the acidity. This process called liming. Liming tends to be expensive and has to be done repeatedly to keep the water from returning to its acidic condition. Furthermore, it only offers a short-term solution at the expense of solving the broader challenges of SO2 and NOx emissions and risks to human health.