Acid RainAcid rain is a serious problem with disastrous effects. Each day this seriousproblem increases, many people believe that this issue is too small to deal withright now this issue should be met head on and solved before it is too late.
Inthe following paragraphs I will be discussing the impact has on the wildlife andhow our atmosphere is being destroyed by acid rain. STATISTICS Although there isvery little data, the evidence indicates that in the last twenty to thirty yearsthe acidity of rain has increased in many parts of the United States. Presently,the United States annually discharges more than 26 million tons of sufferdioxide into the atmosphere. Just three states, Ohio, Indiana, and Illinois areresponsible for nearly a quarter of this total. Overall, two-thirds of thesuffer dioxide into the atmosphere over the United States comes from coal-firedand oil fired plants.
Industrial boilers, smelters, and refineries contribute26%; commercial institutions and residences 5%; and transportation 3%. Theoutlook for future emissions of suffer dioxide is not a bright one. Between nowand the year 2000, United States utilities are expected to double the amount ofcoal they burn. The United States currently pumps some 23 million tons ofnitrogen oxides into the atmosphere in the course of the year. Transportationsources account for 40%; power plants, 30%; industrial sources, 25%; andcommercial institutions and residues, 5%. What makes these figures particularlydistributing is that nitrogen oxide emissions have tripled in the last thirtyyears.
CAUSES Acid rain is a cancer eating into the face of Eastern Canada andthe North Eastern United States. One of the main causes of acid rain is sulphurdioxide. Natural sources which emit this gas are volcanoes, sea spray , rottingvegetation and plankton. However, the burning of fossil fuels, such as coal andoil, are largely to be blamed for approximately half of the emissions of thisgas in the world.
When sulphur dioxide reaches the atmosphere, it oxidizes tofirst form a sulfate ion. It then becomes sulphuric acid as it joins withhydrogen atoms in the air and falls back down to earth. Oxidation occurs themost in clouds and especially in heavily polluted air where other compounds suchas ammonia and ozone help to catalyze the reaction, converting more sulphurdioxide to sulphuric acid. However, not all of the sulphur dioxide is convertedto sulphuric acid.
In fact, a substantial amount can float up into theatmosphere, move over to another area and return to earth unconverted. Thefollowing are the stoichiometric equations for the formation of sulphuric acid:S (in coal) + O2?_ SO2 2 SO2 + O2?_ 2 SO3 SO3?_ + H2O H2SO4 Nitric oxideand nitric dioxide are also components of acid rain. Its sources are mainly frompower stations and exhaust fumes. Like sulfur dioxide, these nitrogen oxidesrise into the atmosphere and are oxidized in clouds to form nitric acid.
Thesereactions are also catalyzed in heavily polluted clouds where iron, manganese,ammonia and hydrogen peroxide are present. In Canada, the main sulfuric acidsources are non-ferrous smelters and power generation. On both sides of theborder, cars and trucks are the main sources for nitric acid(about 40% of thetotal), while power generating plants and industrial commercial and residentialfuel combustion together contribute most of the rest. In the air, the sulfurdioxide and nitrogen oxides can be transformed into sulfuric acid and nitricacid, and air current can send them thousands of kilometers from the source. When the acids fall to the earth in any form it will have large impact on thegrowth or the preservation of certain wildlife. NO DEFENSE One of the directeffects of acid rain is on lakes and its aquatic ecosystems.
There are severalroutes through which acidic chemicals can enter the lakes. Some chemicalsubstances exist as dry particles in the air while others enter the lakes as wetparticles such as rain, snow, sleet, hail, dew or fog. In addition, lakes canalmost be thought of as the “sinks” of the earth, where rain thatfalls on land is drained through the sewage systems eventually make their wayinto the lakes. Acid rain that falls onto the earth washes off the nutrients outof the soil and carries toxic metals that have been released from the soil intothe lakes.
Another harmful way in which acids can enter the lakes is spring acidshock. When snow melts in spring rapidly due to a sudden temperature change, theacids and chemicals in the snow are released into the soils. The melted snowthen runs off to streams and rivers, and gradually make their way into thelakes. The introduction of these acids and chemicals into the lakes causes asudden drastic change in the pH of the lakes – hence the term “spring acidshock”. The aquatic ecosystem has no time to adjust to the sudden change. Areas in Ontario mainly southern regions that are near the Great Lakes, suchsubstances as limestone or other known antacids can neutralize acids enteringthe body of water thereby protecting it.
However, large areas of Ontario thatare near the Pre-Cambrian Shield, with quartzite or granite based geology andlittle top soil, there is not enough buffering capacity to neutralize even smallamounts of acid falling on the soil and the lakes. Therefore over time, thebasic environment shifts from an alkaline to a acidic one. This is why manylakes in the Muskoka, Haliburton, Algonquin, Parry Sound and Manitoulindistricts could lose their fisheries if sulphur emissions are not reducedsubstantially. WHAT IS ACID RAIN? Acidity is measured using a pH scale, with thenumber 7 being neutral. Consequently, a substance with a pH value of less than 7is acidic, while one of a value greater than 7 is basic. It is also worthwhileto note that the pH scale is logarithmic; that is, a substance of pH of 6 is 10times more acidic than another with a pH of 7.
Generally, the pH of 5. 6 has beenused as the baseline in identifying acid rain, although there has been muchdebate over the acceptance of this value. Interestingly enough, a pH of 5. 6 isthe pH value of carbon dioxide in equilibrium with distilled water. Hence, acidran is defined as any rainfall that has an acidity level beyond what is expectedin non-polluted rainfall. In essence, any precipitation that has a pH value ofless than 5.
6 is considered to be acid precipitation. The average mean of pHrainfall in Ontario’s Muskoka-Haliburton lake country ranges between 3. 95 and4. 38 about 40 times more acidic than normal rainfall, while storms inPennsilvania have rainfall pH at 2. 8 it almost has the same rating for vinegar. Already 140 Ontario lakes are completely dead or dying.
An additional 48 000 aresensitive and vulnerable to acid rain due to the surrounding concentrated acidicsoils. ACID RAIN CONSISTS OF. . . .
? Canada does not have as many people, powerplants or automobiles as the United States, and yet acid rain there has becomeso severe that Canadian government officials called it the most pressingenvironmental issue facing the nation. But it is important to bear in mind thatacid rain is only one segment, of the widespread pollution of the atmospherefacing the world. Each year the global atmosphere is on the receiving end of 20billion tons of carbon dioxide, 130 million tons of suffer dioxide, 97 milliontons of hydrocarbons, 53 million tons of nitrogen oxides, more than threemillion tons of arsenic, cadmium, lead, mercury, nickel, zinc and other toxicmetals, and a host of synthetic organic compounds ranging from polychlorinatedbiphenyls(PCBs) to toxaphene and other pesticides, a number of which may becapable of causing cancer, birth defects, or genetic imbalances. COST OF ACIDRAIN Interactions of pollutants can cause problems. In addition to contributingto acid rain, nitrogen oxides can react with hydrocarbons to produce ozone, amajor air pollutant responsible in the United States for annual losses of $2billion to 4. 5 billion worth of wheat, corn, soyabeans, and peanuts.
A widerange of interactions can occur many unknown with toxic metals. In Canada,Ontario alone has lost the fish in an estimated 4000 lakes and provincialauthorities calculate that Ontario stands to lose the fish in 48 500 more lakeswithin the next twenty years if acid rain continues at the present rate. Ontariois not alone, on Nova Scotia’s Eastern most shores, almost every river flowingto the Atlantic Ocean is poisoned with acid. Further threatening a $2 million ayear fishing industry. THE DYING Acid rain is killing more than lakes. It canscar the leaves of hardwood forest, wither ferns and lichens, accelerate thedeath of coniferous needles, sterilize seeds, and weaken the forests to a statethat is vulnerable to disease infestation and decay.
In the soil the acidneutralizes chemicals vital for growth, strips others from the soil and carriesthem to the lakes and literally retards the respiration of the soil. The rate offorest growth in the White Mountains of New Hampshire has declined 18% between1956 and 1965, time of increasingly intense acidic rainfall. Acid rain no longerfalls exclusively on the lakes, forest, and thin soils of the Northeast it nowcovers half the continent. EFFECTS There is evidence that the rain is destroyingthe productivity of the once rich soils themselves, like an overdose of chemicalfertilizer or a gigantic drenching of vinegar. The damage of such overdosing maynot be repairable or reversible.
On some croplands, tomatoes grow to only halftheir full weight, and the leaves of radishes wither. Naturally it rains oncities too, eating away stone monuments and concrete structures, and corrodingthe pipes which channel the water away to the lakes and the cycle is repeated. Paints and automobile paints have its life reduce due to the pollution in theatmosphere speeding up the corrosion process. In some communities the drinkingwater is laced with toxic metals freed from metal pipes by the acidity. As ifurban skies were not already gray enough, typical visibility has declined from10 to 4 miles, along the Eastern seaboard, as acid rain turns into smogs. Amongone of the serious side effects of acid pollution on humans is respiratoryproblems.
The SO2 and NO2 emissions give rise to respiratory problems such asasthma, dry coughs, headaches, eye, nose and throat irritations. An indirecteffect of acid precipitation on humans is that the toxic metals dissolved in thewater are absorbed in fruits, vegetables and in the tissues of animals. Althoughthese toxic metals do not directly affect the animals, they have serious effectson humans when they are being consumed. For example, mercury that accumulates inthe organs and tissues of the animals has been linked with brain damage inchildren as well as nerve disorders, brain damage and death. Similarly, anothermetal, Aluminum, present in the organs of the animals, has been associated withkidney problems and recently, was suspected to be related to Alzheimer’sdisease. Acid particles are also deposited on to buildings and statues, causingcorrosion.
For example, the Capitol building in Ottawa has been disintegratingbecause of excess sulphur dioxide in the atmosphere. Limestone and marble turnto a crumbling substance called gypsum upon contact with the acid, whichexplains the corrosion of buildings and statues. In addition, bridges arecorroding at a faster rate, and the railway industry as well as the airplaneindustry have to expend more money in repairing the corrosive damage done byacid rain. Not only is this an economically taxing problem caused by acid rain,but also a safety hazard to the general public. PREVENTION There are three mainsources of acid deposition: coal in electricity, base metal smelting, and fuelcombustion in vehicles.
There are several ways to reduce SO2 emissions and NOxemissions: 1. Reducing NOx emissions: During Combustion NOx emissions arereduced during combustion are reduced primarily by a process called OverfireAir. In this procedure, a portion of the total air required for the combustionprocess is diverted from the burners to an upper furnace. This causes thecombustion to occur with less O2 than that required, hence slowing down theconversion of atmospheric nitrogen to NO. The process of Low NOx ConcentricFiring operates under the same principal, but involves increases separation ofthe fuel air and secondary air.
After Combustion The catalytic reduction system- This system involves the injection of ammonia gas upstream of the catalyticreaction chamber. This gas will react with NO by the following reaction: 4NO +4NH3 + O2?_ 4N2 + 6H2O It will react with NO2 by the following reaction: 2NO2+ 4NH3 + O2?_ 3N2 + 6H20 The harmless nitrogen gas can then be released intothe atmosphere. 2. Reducing SO2 emissions: Before Combustion 1.
Coal Cleaning -The cleaning of coal was originally used to reduce costs from transporting inertmaterial and improving the quality and uniformity of the coal. However, it hasbeen found to be useful in reducing sulfur content. The cleaning process isperformed gravitationally and is dependent on the density of the sulfur. Theprocess is therefore successful in removing pyritic sulfur (FeS2) due to itshigh specific gravity, and relatively unsuccessful in removing chemically boundorganic sulfur. This method is therefore limited by its dependence on thepercent of pyritic sulfur in the coal. The pyritic sulfur content varies fromregion to region, so those with the highest percentage will be in the highestdemand.
2. Burning of Low Sulfur Coals – Some power plants have chosen to reducetheir sulfur dioxide emissions by burning coal of low sulfur content. (Subbituminouscoal is of lower sulfur content than bituminous coal. ) A process is veryexpensive, due to the high demand for subbituminous coal.
During Combustion 1. FBC – Fluidized Bed Combustion – This process allows sulfur dioxide emissions tobe reduced during the combustion process. A limestone or sand bed are crushedand fluidized. It is essential that a balance is established between the heatliberated within the bed from fuel combustion, and the heat removed by the fluegas as it leaves.
The limestone is able to react with the SO2 and reduceemissions by over 90%. After Combustion 1. Wet Flue Gas Desulfurization – Thisis a highly effective and cost efficient system of flue gas desulfurization. Thewet scrubber is located downstream of the boiler, and consists of eitherlimestone, lime, or sodium hydroxide. Limestone is the most popular choice andreacts with the gas by the following reaction: CaCO3 + SO2 + H2O + O2?_ CaSO3+ CaSO4 + CO2 + H2O The flue gas enters the absorber and is re-emitted afterbeing scrubbed, at which time the waste solids are removed and disposed of.
2. Dry Scrubbing – The process of dry scrubbing involves the contact between dryinggas and the atomized liquid (alkaline based). Upon contacting the flue gas, thedrying gas will convert the atomized droplets into a dry product that can beseparated and disposed of. The dry scrubbing process requires less power tocomplete than wet scrubbing. FINAL THOUGHTS Acid rain is very real and a verythreatening problem.
Action by one government is not enough. In order for thingsto be done we need to find a way to work together on this for at least areduction in the contaminates contributing to acid rain. Although there areright steps in the right directions but the government should be cracking downon factories not using the best filtering systems when incinerating or if thefactory is giving off any other dangerous fumes.
