<MPQA autoclass="obj" certainty="24.0">The principal natural phenomena that contribute acid-producing gases to the atmosphere are emissions from volcanoes and from biological processes that occur on the land, in wetlands, and in the oceans.</MPQA>
<MPQA autoclass="obj" certainty="25.7">The effects of acidic deposits have been detected in glacial ice thousands of years old in remote parts of the globe.</MPQA>
<MPQA autoclass="obj" certainty="23.7">Principal human sources are industrial and power-generating plants and transportation vehicles.</MPQA>
<MPQA autoclass="obj" certainty="23.5">The gases may be carried hundreds of miles in the atmosphere before they are converted to acids and deposited.</MPQA>
<MPQA autoclass="obj" certainty="21.5">Industrial acid rain is a substantial problem in China, Eastern Europe, Russia and areas down-wind from them.</MPQA>
<MPQA autoclass="obj" certainty="11.0">These areas all burn sulfur-containing coal to generate heat and electricity.</MPQA>
<MPQA autoclass="obj" certainty="25.3">Acid rain is defined as rain with a pH of below 4.0 - 4.5.</MPQA>
<MPQA autoclass="obj" certainty="18.3">Normal rain has a pH of about 5.6, which is slightly acidic.</MPQA>
<MPQA autoclass="obj" certainty="16.7">This natural acidity is caused by dissolved carbon dioxide dissociating to form weak carbonic acid.</MPQA>
<MPQA autoclass="obj" certainty="21.0">'Acid rain' is caused by sulfur from impurities in fossil fuels and nitrogen from the air combining with oxygen to form sulfur and nitrogen dioxides.</MPQA>
<MPQA autoclass="obj" certainty="6.2">These diffuse into the atmosphere and react with water to form sulfuric and nitric acids which are soluble and fall with the rain.</MPQA>
<MPQA autoclass="obj" certainty="21.3">Some hydrochloric acid is also formed.</MPQA>
<MPQA autoclass="obj" certainty="14.6">A possible reaction for the production of acid rain is as follows:Evidence for an increase in the levels of acid rain comes from analysing layers of glacial ice.</MPQA>
<MPQA autoclass="obj" certainty="15.5">These show a sudden increase in pH from the start of the industrial revolution of 6 to 4.5 or 4. Other information has been gathered from studying organisms known as diatoms which inhabit ponds.</MPQA>
<MPQA autoclass="obj" certainty="25.7">Over the years these die and are deposited in layers of sediment on the lakes bottom.</MPQA>
<MPQA autoclass="obj" certainty="22.0">Diatoms thrive in certain pHs, so the numbers of diatoms found in layers of increasing depth give an indication of the change in pH over the years.</MPQA>
<MPQA autoclass="obj" certainty="19.2">Since the industrial revolution, emissions of sulfur and nitrogen oxides to the atmosphere have increased.</MPQA>
<MPQA autoclass="obj" certainty="7.9">Industrial and energy-generating facilities that burn fossil fuels, primarily coal, are the principal sources of increased sulfur oxides.</MPQA>
<MPQA autoclass="obj" certainty="25.2">Occasional pH readings of well below 2.4 (the acidity of vinegar) have been <MPQA autoclass="objectiveSpeech">reported</MPQA> in industrialized areas.</MPQA>
<MPQA autoclass="obj" certainty="21.6">These sources, plus the transportation sector, are the major originators of increased nitrogen oxides.</MPQA>
<MPQA autoclass="obj" certainty="14.9">The problem of acid rain not only has increased with population and industrial growth, it has become more widespread.</MPQA>
<MPQA autoclass="obj" certainty="13.9">The use of tall smokestacks to reduce local pollution has contributed to the spread of acid rain by releasing gases into regional atmospheric circulation.</MPQA>
<MPQA autoclass="subj" certainty="6.2">Often deposition occurs a considerable distance from its formation, with mountainous regions tending to receive the most (simply because of their higher rainfall).</MPQA>
<MPQA autoclass="subj" certainty="8.9">An example of this effect is the frequent high pH of rain which <MPQA autoclass="negative">falls</MPQA> in Scandinavia compared to the oxide levels it gives off.</MPQA>
<MPQA autoclass="obj" certainty="15.0">There is a strong relationship between higher pHs and the lowering of populations of fish in lakes.</MPQA>
<MPQA autoclass="obj" certainty="18.7">Below 4.5 virtually no fish survive, whereas levels of 6 or higher promote healthy populations.</MPQA>
<MPQA autoclass="obj" certainty="20.8">Acid in water inhibits the production of enzymes which enable trout larvae to escape their eggs.</MPQA>
<MPQA autoclass="obj" certainty="13.5">It also mobilises toxic metals such as aluminium in lakes.</MPQA>
<MPQA autoclass="obj" certainty="15.0">Aluminium causes some fish to produce an excess of mucus around their gills, preventing proper ventilation.</MPQA>
<MPQA autoclass="obj" certainty="16.9">Phytoplankton growth is inhibited by high acid levels, and animals which feed on it suffer.</MPQA>
<MPQA autoclass="obj" certainty="14.4">Many lakes are subject to natural acid runoff from acid soils, and this can be triggered by particular rainfall patterns that concentrate the acid.</MPQA>
<MPQA autoclass="obj" certainty="4.3">An acid lake with newly-dead fish is not evidence of severe air-pollution.</MPQA>
<MPQA autoclass="obj" certainty="23.3">Trees are harmed by acid rain in a variety of ways.</MPQA>
<MPQA autoclass="obj" certainty="23.9">The waxy surface of leaves is broken down and nutrients are lost, making trees more susceptible to frost, fungus and insects.</MPQA>
<MPQA autoclass="obj" certainty="20.6">Root growth slows and as a result less nutrients are taken up.</MPQA>
<MPQA autoclass="subj" certainty="20.8"><MPQA autoclass="negative">Toxic</MPQA> ions are mobilised in the soil, and valuable minerals are leached away or (in the case of phosphate) become bound to clay.</MPQA>
<MPQA autoclass="subj" certainty="39.5">The <MPQA autoclass="negative">toxic</MPQA> ions released due to acid rain forms the greatest <MPQA autoclass="negative">threat</MPQA> to humans.</MPQA>
<MPQA autoclass="subj" certainty="14.7">Mobilised copper has been <MPQA autoclass="negative">implicated</MPQA> in <MPQA autoclass="negative">outbreaks</MPQA> of diarrhoea in young children and it is <MPQA autoclass="speechDirectSubjective">thought</MPQA> there are links between water supplies contaminated with aluminium and Alzheimer's <MPQA autoclass="negative">disease</MPQA>.</MPQA>
<MPQA autoclass="obj" certainty="21.0">SolutionsIn the U.S., coal-burning power plants are required to use flue gas desulfurisation system(FGD) to remove sulfur-containing gases from their stack gases.</MPQA>
<MPQA autoclass="obj" certainty="20.4">An example of FGD is the wet scrubber which is commonly used in the U.S. and many other countries.</MPQA>
<MPQA autoclass="obj" certainty="18.0">A wet scrubber is basically a reaction tower equipped with a fan that extracts hot smoky stack gases from a power plant into the tower.</MPQA>
<MPQA autoclass="obj" certainty="22.1">Lime or limestone in slurry form is also injected into the tower to mix with the stack gases and combine with the sulphur dioxide present.</MPQA>
<MPQA autoclass="obj" certainty="27.5">The calcium carbonate of the limestone produces pH-neutral calcium sulfate that is physically removed from the scrubber.</MPQA>
<MPQA autoclass="obj" certainty="26.7">That is, the scrubber turns sulfur pollution into industrial sulfates.</MPQA>
<MPQA autoclass="obj" certainty="26.1">In some areas the sulfates are sold to chemical companies as gysum when the purity of calcium sulfate is high.</MPQA>
<MPQA autoclass="obj" certainty="10.0">In others, they are placed in a land-fill.</MPQA>
<MPQA autoclass="subj" certainty="6.5">Some people <MPQA autoclass="negative">oppose</MPQA> regulation of power-generation, <MPQA autoclass="speechDirectSubjective">believing</MPQA> that power-generation and <MPQA autoclass="negative">pollution</MPQA> are required to go together.</MPQA>
<MPQA autoclass="subj" certainty="12.8">This is <MPQA autoclass="negative">false</MPQA>.</MPQA>
<MPQA autoclass="subj" certainty="7.8">Nuclear reactors generate less than one-millionth the <MPQA autoclass="negative">toxic</MPQA> <MPQA autoclass="negative">waste</MPQA> (measured by net biological effect) per watt, when <MPQA autoclass="negative">wastes</MPQA> of both power-generation facilities are properly handled (USA forbids nuclear recycling, so that country produces more "<MPQA autoclass="negative">waste</MPQA>" than other countries).</MPQA>
<MPQA autoclass="subj" certainty="6.8">An even more benign regulatory <MPQA autoclass="negative">scheme</MPQA> involves emission trading.</MPQA>
<MPQA autoclass="obj" certainty="17.6">In this scheme , every current polluting facility is given an emissions license that becomes part of capital equipment.</MPQA>
<MPQA autoclass="obj" certainty="24.1">Operators can then install pollution control equipment, and sell parts of their emissions licenses.</MPQA>
<MPQA autoclass="obj" certainty="16.0">The main effect of this is to give operators real economic incentives to install pollution controls.</MPQA>
<MPQA autoclass="obj" certainty="0.4">Since public interest groups can retire the licenses by purchasing them, the net result is a continuously decreasing and more diffused set of pollution sources.</MPQA>
<MPQA autoclass="obj" certainty="19.0">At the same time, no particular operator is ever forced to spend money without a return of value from commercial sale of assets.</MPQA>
<MPQA autoclass="obj" certainty="29.1">Retrieved from "http://en.wikipedia.org/wiki/Acid_rain"</MPQA>
<MPQA autoclass="obj" certainty="31.7">Categories: Environment</MPQA>