0 Acid Deposition6.1 Introduction Acid deposition is ageneral name for a number of phenomena, namely acid rain, acid fog and acidmist. It occurs during the combustion of fossil fuels and otherindustrial processes undergo complex chemical reactions and emitted gases inthe atmosphere. These gases it then emitted to the Earth as wet deposition ordry deposition. Acid deposition cancause harmful effect on environment.
For wet deposition, it occurs when theacidic chemicals in the air is blew by wing and transport to the areas wherethe weather is wet. Then, these acidic chemicals will fall to the ground in theform of rain, sleet, fog, snow or mist which is the type of wet deposition.This will cause the acid to be remove from atmosphere and deposit on theEarth’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, itoccurs when the acidic chemicals in the air is blew by wing and transport tothe 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 dryparticles. They will stick to the buildings, cars, houses and trees. Acid deposition is usually caused bythe accumulation of acids or acidic compounds on the Earth’s surface.
The main chemical precursorsare sulphur 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 acidrain that is more acidic than normal has been linked to air pollution. Acidrain damage historic artworks, statues, and classic architecture and erodesnames, dates and marking on cemetery gravestones. It also impairs theproduction of fish. 6.2 Causes Emission of chemical gases such as sulphurdioxide (SO2) and nitrogen oxides (NOX) into the atmosphereare major contributor to acid deposition.
This mainly cause by man-madesources. SO2 and NOX gases are emitted through humanactivities. These chemical gases can be released from factories, particularlyin hear and power generation facilities, large industrial boilers, action ofbacteria on fertilisers or vehicle exhaust. There gases are reactive and they will react withthe water, oxygen or other chemicals substances in the atmosphere to form more acidicpollutants. This reaction can cause the formation of several acidic compoundslike nitric acid, sulphuric acid and ammonium nitrate. Acid deposition in this area should bevery high. On the other hand, a small amount of chemical gasesis come from natural sources. For example, they can come from volcanic gases whichcontain sulphur dioxide.
Most of these gases are come from the use of combustionof fossil fuels to generate electricity. Also, natural source like lightning strikescan produces oxides of nitrogen that will react with the water to form acid rain. SO2 and NOX canbe blew by wind and transport over long distances to other areas. This result inthe spreading of acid deposition and cause negative impact on environment, buildingsand living things. 6.
3Process Burningof hydrocarbon fuels produce sulphur dioxide (SO2).S+ O2 ? SO2SO2+ H2O (rain water) + O2 (Oxygen in air) ? H2SO4(Acid Deposition) Nitrogenand oxygen combine to make oxides of nitrogen.N2+ 2O2 ? 2NO2 H2O(rain water) + O2 (Oxygen in air) ? HNO3 (Acid Deposition) 6.4Effects Acid rain has many ecological effects, but none is greater than itsimpact on lakes, streams, wetlands, and other aquatic environments. Acid rain either falls directlyon aquatic bodies or gets run off the forests, roads and fields to flow intostreams, rivers and lakes makes waters acidic, which lower the overall pH of waterbody. Theaquatic 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 thesurvival of aquatic life. Acid rainalso damages forests, especially those at higher elevations. It robs the soilof essential nutrients and releases aluminium in the soil, which makes it hardfor trees to take up water. It makes trees vulnerable to disease, extremeweather, and insects by destroying their leaves, damaging the bark andarresting their growth.
Moreover, acid rain can have destructiveeffect on many objects, including buildings, statues, monuments, andcars. The chemicals found in acid rain can cause paint to peel and stonestatues to begin to appear old and worn down, which reduces their value andbeauty. For example, acid rain will eventuallydissolve a marble statue. Acid rain often contains sulphuric acid, H2SO4, which will react withthe calcium carbonate, CaCO3, toproduce relatively insoluble calcium sulphate, CaSO4, carbondioxide, CO2, and water, H2O.CaCO3 (s) + H2SO4(aq)?CaSO4(s) + CO2 (g) + H2O(l)If large quantitiesof water are present, the calcium sulphate will be removed from the surface ofthe statue. In time, the quantities of calcium carbonate converted by acidrains into calcium sulphate, water, and carbon dioxide will become quitevisible.
6.5Solutions One of the most fundamental solutions is to utilize fuels that burn morecleanly, or to burn coal more efficiently. This will greatly reduce the amountof acids released in the atmosphere. Besides fossil fuels, there is a widerange of alternative energy sources that can generate electricalpower. 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 costsas well as benefits. The only solution is using sustainableenergy that can protect the future. On theother hand, individuals can help to prevent acid rain by conserving energy. A small step can be taken by the individualby turning off the lights, computers, and other electrical appliances, when notin use. The less electricitypeople use in their homes, the fewer chemicals power plants will emit. While purchasing, individual can buy theappliances, which consume less energy.
Vehicles are also major fossil fuel users, so drivers can reduce emissions byusing public transportation, carpooling, biking, or simply walking whereverpossible to nearby places instead ofdriving. This can help us save fuel and gas, as well as reduce the adverseeffects. Lastly, there are some things that people cando to repair the damage caused by acid rain to lakes and rivers. Limestone orlime can be added to acidic surface waters to balances the acidity. Thisprocess, called liming. Liming tends to be expensive, and has to be donerepeatedly to keep the water from returning to its acidic condition.Furthermore, it only offers a short-term solution at the expense ofsolving the broader challenges of SO2 and NOx emissions and risks tohuman health.