SCRAP BOOK of Muet ( Hmwrk)

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    SCRAP BOOK

    of

    Environmental Issue

    Acid Rain

    Name: Priscilla Heng Shin Yun

    Class : 6BS1

    Muet Teacher : Puan Shanta

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    Wha Ac d Ra ???

    Acid rain is a rain or any other form ofprecipitation that is unusually acidic, meaning that it

    possesses elevated levels of hydrogen ions (lowpH).Acid rain is a popular term for the

    atmospheric deposition of acidified rain, snow, sleet, hail, acidifying gases and particles, as

    well as acidified fog and cloud water. The increasedacidity of these depositions, primarily

    from the strong acids, sulphuric and nitric, is generated as a by-product of the combustion of

    fuels containing sulphur ornitrogen, especially fossil fuel power plants. The heating of

    homes, electricity production, and driving vehicles all rely primarily on fossil fuel energy.

    When fossil fuels are combusted, acid-forming nitrogen and sulphur oxides are released to

    the atmosphere. These compounds are transformed in the atmosphere, often travelling

    thousands ofkilometers from their original source, and then fall out on land and water

    surfaces as acid rain. As a result, pollutants from power plants in New Jersey or Michigan can

    impact pristine forests or lakes in undeveloped parts of New Hampshire or Maine.). Acid

    Rain can have harmful effects on plants, aquatic animals, and infrastructure through the

    process of wet deposition. Acid rain is caused by emissions ofsulphur dioxide and nitrogenoxides which react with the watermolecules in the atmosphere to produce acids.

    Governments have made efforts since the 1970s to reduce the release of sulfur dioxide into

    the atmosphere with positive results. Nitrogen oxides can also be produced naturally

    by lightning strikes and sulphur dioxide is produced by volcanic eruptions.

    A more accurate term for acid rain is acid deposition. Distilled water, once carbon

    dioxide is removed, has a neutral pH of 7. Liquids with a pH less than 7 are acidic, and

    those with a pH greater than 7 are alkaline.

    Clean or unpolluted rain has a slightly acidic pH of over 5.7, because carbon dioxide

    and water in the air react together to form carbonic acid, but unpolluted rain also

    contains other chemicals.[1]

    H2O (l) + CO2 (g) H2CO3 (aq)

    Carbonic acid then can ionize in water forming low concentrations

    ofhydronium and carbonate ions:

    H2O (l) + H2CO3 (aq) HCO3 (aq) + H3O+ (aq)

    Acid deposition as an environmental issue would include additional acids

    to H2CO3.

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    Historyofacidrain in theUnitedStates

    Since 1998, Harvard University wraps some of the bron

    e and marble statues on its

    campus, such as this "Chinese stele", with waterproof covers every winter, in order to

    protect them from erosion caused b y acid rain (or, actually, acid snow)[16]

    In 1980, the U.S. Congress passed an Acid Deposition Act. This Act established a

    10-year research program under the direction of the National Acidic Precipitation

    Assessment Program (NAPAP).

    NAPAP looked at the entire problem. It enlarged a network of monitoring sites to

    determine how acidic the precipitation actually was, and to determine long term

    trends, and established a network for dry deposition. It looked at the effects of acidrain and funded research on the effects of acid precipitation on freshwater and

    terrestrial ecosystems, historical buildings, monuments, and building materials. It

    also funded extensive studies on atmospheric processes and potential control

    programs.

    In 1991, NAPAP provided its first assessment of acid rain in the United States. It

    reported that 5% of New England Lakes were acidic, with sulfates being the most

    common problem. They noted that 2% of the lakes could no longer support Brook

    Trout, and 6% of the lakes were unsuitable for the survival of many species of

    minnow.

    Subsequent Reports to Congress have documented chemical changes in soil and

    freshwater ecosystems, nitrogen saturation, decreases in amounts of nutrients in

    soil, episodic acidification, regional ha e, and damage to historical monuments.

    Meanwhile, in 1990, the USCongress passed a series of amendments to theClean

    Air Act. Title IV of these amendments established the Acid Rain Program, a cap

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    and trade system designed to control emissions of sulphur dioxide and nitrogen

    oxides. Title IV called for a total reduction of about 10 million tons of SO2

    emissions from power plants. It was implemented in two phases.

    Phase I began in 1995, and limited sulphur dioxide emissions from 110 ofthe

    largest power plants to a combined total of 8.7 million tons of sulphur dioxide. Onepower plantin New England (Merrimack) was in Phase I. Four other plants

    (Newington, Mount Tom, Brayton Point, and Salem Harbor) were added under

    other provisions ofthe program.

    Phase II began in 2000, and affects most ofthe power plants in the country.

    During the 1990s, research continued. On March 10, 2005, EPA issued the Clean

    Air Interstate Rule (CAIR). This rule provides states with a solution to the problem

    of power plant pollution that drifts from one state to another. CAIRwill

    permanently cap emissions of SO2 and NOx in the eastern United States. When

    fully implemented, CAIRwill reduce SO2 emissions in 28 eastern states and the

    District of Columbia by over 70 percent and NOx emissions by over 60 percent

    from 2003 levels.

    Overall, the Program's cap and trade program has been successfulin achieving its

    goals. Since the 1990s, SO2 emissions have dropped 40%, and according to

    the Pacific Research Institute, acid rain levels have dropped 65% since

    1976. However, this was significantly less successfulthan conventional regulation

    in the European Union, which saw a decrease of over 70% in SO2 emissions during

    the same time period.

    In 2007, total SO2 emissions were 8.9 million tons, achieving the program's long

    term goal ahead ofthe 2010 statutory deadline.

    The EPA estimates that by 2010, the overall costs of complying with the program

    for businesses and consumers will be $1 billion to $2 billion a year, only one fourth

    of what was originally predicted.

    Acid rain was discovered in 1963 in North America atthe Hubbard Brook ExperimentalForest, site ofthe Hubbard Brook Ecosystem Study in the White Mountains of NewHampshire, in rain that was some 100 times more acidic than unpolluted rain. Innovations forreducing fossil fuel emissions, such as scrubbers upstream ofthe tall smoke stacks on power

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    plants and factories, catalytic converters on automobiles, and use oflow-sulphurcoal, havebeen employed to reduce emissions ofsulphur dioxide (SO2) and nitrogen oxides (NOx). As a

    result ofincreasing global economies, fossil fuel combustion is increasing around the world,with concomitant spread of acid rain.

    Emissions of chemicals lea

    ing to aci

    ification

    The mostimportant gas which leads to acidification is sulphur dioxide. Emissions of nitrogen

    oxides which are oxidized to form nitric acid are ofincreasing importance due to stricter

    controls on emissions of sulphur containing compounds. 70 Tg(S) per yearin the form of

    SO2 comes from fossil fuel combustion and industry, 2.8 Tg(S) from wildfires and 7-8 Tg(S)

    per year from volcanoes.

    Natural phenomena

    The principal naturalphenomenathat contribute acid-producing gases to the atmosphere are

    emissions from volcanoes. Thus, for example, fumaroles from Laguna Caliente crater ofPos

    Volcano create extremely high amounts of acid rain and fog with acidity 2 of pH, clearing an

    area of any vegetation and frequently causing irritation to the eyes and lungs ofinhabitants in

    nearby settlements. Acid-producing gasses are created also bybiological processes that

    occur on the land, in wetlands, and in the oceans. The major biological source of sulfur

    containing compounds is dimethyl sulphide.

    Nitric acid in rainwateris an important source of fixed nitrogen for plantlife, and is also

    produced by electrical activity in the atmosphere such as lightning.

    Acidic deposits have been detected in glacialicethousands of years old in remote parts ofthe

    globe.[13]

    Soils of Coniferous forests are naturally very acidic due to the shedding of needles and this

    phenomenon should not be confused with acid rain.

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    Humansactivitity

    The coal-fired Gavin Power Plant inCheshire, Ohio

    The principal cause of acid rain is sulfur and nitrogen compounds from human sources,

    such as electricity generation, factories, and motor vehicles. Coal power plants are one of

    the most polluting. The gases can be carried hundreds of kilometers in the atmosphere

    before they are converted to acids and deposited. In the past, factories had short funnels to

    let out smoke but this caused many problems locally; thus, factories now have taller smoke

    funnels. However, dispersal from these taller stacks causes pollutants to be carried farther,

    causing widespread ecological damage. Also, livestock production plays a major role. It is

    responsible for almost two-thirds of all sources ofammonia produced through human

    activities, which contributes significantly to acid rain.

    Chemica

    processes

    Combustion of fuels creates sulphur dioxide and nitric oxides. They are converted

    into sulphuric acid and nitric acid.

    Gasphasechemistry

    In the gas phase sulphur dioxide is oxidi ed by reaction with the hydroxyl radical via

    an intermolecularreaction:[5]

    SO2 + OH HOSO2

    which is followed by:

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    HOSO2 + O2 HO2 + SO3

    In the presence of water, sulphur trioxide (SO3) is converted rapidly to sulphuric acid:

    SO3 (g) + H2O (l) H2SO4 (l)

    Nitrogen dioxide reacts with OH to form nitric acid:

    NO2 + OH HNO3

    Chemistry inc

    ouddrop

    ets

    When clouds are present, the loss rate ofSO

    2 is faster than can be explained by gas phase chemistryalone. This is due to reactions in the liquid water droplets.

    Hydrolysis

    Sulphur dioxide dissolves in water and then, like carbon dioxide, hydrolyses in a series

    ofequilibrium reactions:

    SO2 (g) + H2O SO2H2O

    SO2H2O H+ + HSO3

    HSO3

    H+

    + SO32

    Oxidation

    There are a large number of aqueous reactions that oxidi e sulphur from S(IV) to S(VI), leading to the

    formation of sulphuric acid. The most important oxidation reactions are with o one, hydrogen

    peroxide and oxygen (reactions with oxygen are cataly ed by iron and manganese in the cloud

    droplets).

    Aciddeposition

    Wetdeposition

    Wet deposition of acids occurs when any form of precipitation (rain, snow, and so on.) removes acids

    from the atmosphere and delivers it to the Earth's surface. This can result from the deposition of acids

    produced in the raindrops (see aqueous phase chemistry above) or by the precipitation removing the

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    acids eitherin clouds or below clouds. Wet removal of both gases and aerosols are both ofimportance

    for wet deposition.

    Dry

    eposition

    Acid deposition also occurs via dry deposition in the absence of precipitation. This can be responsible

    for as much as 20 to 60% oftotal acid deposition. This occurs when particles and gases stickto the

    ground, plants or other surfaces.

    Precipitation chemistry

    Sever pr esses can resu tin the for ation of aci deposition. Nitrogen oxides (NOx and su phur

    dioxide (SO2) released into the at osphere from a variet ofsources call fall to the ground simply as dry

    deposition. This dry deposition can then be converted into acidswhen these deposited chemicals meetwater. Mostwetacid deposition formswhen nitrogen oxides (NOx) and sulphur dioxide (SO2) are

    converted to nitric acid (HNO3) and sulphuric acid (H2SO4) through oxidation and dissolution. Wet

    deposition can also form when ammonia gas (NH3) from natural sourcesis converted into ammonium

    (NH4). (Source: PhysicalGeography.net)

    The source ofthe acids released to the atmosphereis the largely the combustion of fossilfuels that produce waste by-products including gases such as oxides of sulphurand nitrogen. Ammonia (NH3) is a by-product of some natural processes, as wellas agricultural sources (e.g., application of nitrogen fertilizers; confined animal feedlots). In

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    its dissolved form (NH4+) it contributes acidity to surface waters through the process

    of nitrification. Oxidized sulphur and nitrogen gases are acid precursors in the atmosphere.

    For example, SO2reacts with waterin the atmosphere to yield sulphuric acid:SO2 + H2O + O2 = H2SO4

    An analogous reaction of water with nitrogen oxides, symbolized as NOx , yields nitric acid(HNO3).In addition to wet deposition (rain, snow, and fog), acidic deposition includes the depositionof dry, particulate, and gaseous acid precursors that become acidic in contact with moisture.This dry deposition is difficultto quantify and expensive to measure. Inferential methods

    indicate that dry deposition represents 20% to 80% ofthe total deposition of acids to thelandscape, depending on factors such as location, season, and total rainfall.

    The pH scale. A value of 7.0 is considered neutral. Values higherthan 7.0 are increasingly

    alkaline or basic. Values lowerthan 7.0 are increasingly acidic. The illustration above alsodescribes the pH of some common substances.

    (Source:Physical eography.net)

    Natural sources can also contribute additional acidity toprecipitation. Natural emissions cancome from wetlands and geologic sources. Major natural sources of NOxinclude lightningand soil microbes. Organic acidity may arise from freshwater wetlands and coastalmarshes.Itis these natural sources thatlead to the inference that pre-industrial precipitation in forestedregions had apH around 5.0. Iftrue, then modern precipitation in the North and Eastis two tothree times more acidic than pre-industrial.

    The acidity of precipitation is still subjectto misunderstanding. Even in pristineenvironments, precipitation pH is rarely controlled by the carbon dioxide (CO2) reaction thathas an equilibrium pH of 5.6:

    H2O + CO2 = H2CO3

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    Because ofthe many sources of acidity in precipitation, pH 5.6 is notthe benchmark normal

    pH against which the acidity of modern precipitation should be compared. Precipitation is avariable and complex mixture of particulates and solutes derived from local sources and long-

    range transport.

    For example, in arid or partly forested regions, dust from soil and bedrocktypicallyneutralizes both the natural and human sources of acidity in precipitation, yielding a solutionthat may be quite basic (pH greaterthan 7).

    In the northeastern U.S. and eastern Canada, annual precipitation pH ranges from 4.3 inPennsylvania, New York, and Ohio, to 4.8 in Maine and maritime Canada.

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    Adverseeffects

    This chart shows that not all fish, shellfish, or the insects that they eat

    can tolerate the same amount of acid; for example, frogs can tolerate

    water that is more acidic (i.e., has a lower pH) than trout.

    Acid rain has been shown to have adverse impacts on forests, freshwaters and soils, killing insect and

    aquatic life-forms as well as causing damage to buildings and having impacts on human health.

    Surfacewatersandaquaticanimals

    Both the lower pH and higher aluminium concentrations in surface water that occur as a result of acid

    rain can cause damage to fish and other aquatic animals. At pHs lower than 5 most fish eggs will not

    hatch and lower pHs can kill adult fish. As lakes and rivers become more acidic biodiversity is

    reduced. Acid rain has eliminated insect life and some fish species, including thebrook trout in some

    lakes, streams, and creeks in geographically sensitive areas, such as the Adirondack Mountains of the

    United States. However, the extent to which acid rain contributes directly or indirectly via runoff from

    the catchment to lake and river acidity (i.e., depending on characteristics of the surrounding

    watershed) is variable. The United States Environmental Protection Agency's (EPA) website states:

    "Of the lakes and streams surveyed, acid rain caused acidity in 75 percent of the acidic lakes and

    about 50 percent of the acidic streams".

    Soils

    Soil biology and chemistry can be seriously damaged by acid rain. Some microbes are unable to

    tolerate changes to low pHs and are killed. The en ymes of these microbes are denatured (changed in

    shape so they no longer function) by the acid. The hydronium ions of acid rain also

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    mobili e toxins such as aluminium, and leach away essential nutrients and minerals such

    as magnesium.

    2 H+

    (aq) + Mg2+

    (clay) 2 H+

    (clay) + Mg2+

    (aq)

    Soil chemistry can be dramatically changed when base cations, such as calcium and magnesium, are

    leached by acid rain thereby affecting sensitive species, such as sugar maple (Acer saccharum).

    Forestsandothervegetation

    Effect of acid rain on a forest, Jizera Mountains, Czech

    Republic

    Adverse effects may be indirectly related to acid rain, like the acid's effects on soil (see above) or high

    concentration of gaseous precursors to acid rain. High altitude forests are especially vulnerable as they

    are often surrounded by clouds and fog which are more acidic than rain.

    Other plants can also be damaged by acid rain, but the effect on food crops is minimi ed by the

    application of lime and fertili ers to replace lost nutrients. In cultivated areas, limestone may also be

    added to increase the ability of the soil to keep the pH stable, but this tactic is largely unusable in the

    case of wilderness lands. When calcium is leached from the needles of red spruce, these trees become

    less cold tolerant and exhibit winter injury and even death.

    Humanhealtheffects

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    Acid rain does not directly affect human health. The acid in the rainwater is too dilute to have direct

    adverse effects. However, the particulates responsible for acid rain (sulphur dioxide and nitrogen

    oxides) do have an adverse effect. Increased amounts of fine particulate matter in the air do contribute

    to heart and lung problems including asthma and bronchitis.

    Otheradverseeffects

    Effect of acid rain on statues

    Acid rain can also damage buildings and historic monuments, especially those made of rocks such

    as limestone and marble containing large amounts of calcium carbonate. Acids in the rain react with

    the calcium compounds in the stones to create gypsum, which then flakes off.

    CaCO3 (s) + H2SO4 (aq) CaSO4 (aq) + CO2 (g) + H2O (l)

    The effects of this are commonly seen on old gravestones, where acid rain can cause the inscriptions

    to become completely illegible. Acid rain also increases the oxidation rate of metals, in

    particularcopperandbron e.

    Affected areas

    Places with significant impact by acid rain around the globe include most of eastern Europe

    fromPoland northward into Scandinavia, the eastern third of the United States, and

    southeastern Canada. Other affected areas include the southeastern coast ofChina and Taiwan.]

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    Prevention metho sBecause of these problems and the adverse effects air pollution has on human

    health, a number of steps are being taken to reduce sulfur and nitrogen

    emissions. Most notably, many governments are now requiring energy producers

    to clean smoke stacks by using scrubbers which trap pollutants before they are

    released into the atmosphere and catalytic converters in cars to reduce their

    emissions. Additionally, alternative energy sources are gaining more

    prominence today and funding is being given to the restoration of ecosystems

    damaged by acid rain worldwide .

    Technical solutions

    Many coal-burningpower plants use Flue gas desulfurization (FGD) to remove sulphur-containing

    gases from their stack gases. For a typical coal-fired power station, FGD will remove 95 percent or

    more ofthe SO2 in the flue gases. An example of FGD is the wet scrubber which is commonly used.

    A wet scrubberis basically a reaction tower equipped with a fan that extracts hot smoke stack gases

    from a power plantinto the tower. Lime orlimestone in slurry form is also injected into the towerto

    mix with the stack gases and combine with the sulphur dioxide present. The calcium carbonate ofthe

    limestone produces pH-neutral calcium sulphate thatis physically removed from the scrubber. Thatis,

    the scrubberturns sulphur pollution into industrial sulphates.

    In some areas the sulphates are sold to chemical companies as gypsum when the purity of calcium

    sulphate is high. In others, they are placed in landfill. However, the effects of acid rain can last for

    generations, as the effects of pH level change can stimulate the continued leaching of undesirable

    chemicals into otherwise pristine water sources, killing off vulnerable insect and fish species and

    blocking efforts to restore native life.

    Vehicle emissions control reduces emissions of nitrogen oxides from motor vehicles.

    International treaties

    A number ofinternationaltreaties on the long range transport of atmospheric pollutants have been

    agreed for example, Sulphur Emissions Reduction Protocol underthe Convention on Long-Range

    Transboundary Air Pollution. Canada and the US signed the Air Quality Agreementin 1991. Most

    European countries and Canada have signed the treaties.

    Emissions traing

    In this regulatory scheme, every current polluting facility is given or may purchase on an open market

    an emissions allowance for each unit of a designated pollutantit emits. Operators can then install

    pollution control equipment, and sell portions oftheir emissions allowances they no longer need for

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    their own operations, thereby recovering some ofthe capital cost oftheirinvestmentin such

    equipment. The intention is to give operators economic incentives to install pollution controls.

    The first emissions trading market was established in the United States by enactment ofthe Clean Air

    Act Amendments of 1990. The overall goal ofthe Acid Rain Program established by the Actis to

    achieve significant environmental and public health benefits through reductions in emissions of

    sulphur dioxide (SO2) and nitrogen oxides (NOx), the primary causes of acid rain. To achieve this goal

    atthe lowest costto society, the program employs both regulatory and market based approaches for

    controlling air pollution.

    Article about aci rain

    Forests fall silent with acid rainBirds could disappear from North American forests because of acidrain.

    Scientists have found that the pollutant is leading to a decline of

    one species at least.

    It seems to affect the breeding habits of the wood thrush.

    The bird lives on mountain slopes of the

    Eastern United States when it visits to breedduring the summer.

    A drop in numbers has been seen since the1960s.

    Research into its disappearance has focused until now on habitatloss and destruction.

    olunteer help

    In the latest study, a team at Cornell University looked at a

    possible link between acid rain, soil acidity and impaired breedingbehaviour.

    This is far from the onlythreat against the bird

    Ralph Hames, Cornell

    University

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    They were helped by an army of amateur volunteers who collecteddata on the wood thrush across its territory range.

    The scientists found a significant negative effect of acid rain on thelikelihood of the bird breeding.

    "When looking for causes of declines we have to consider changes

    to the environment in addition to simple habitat loss orfragmentation," Ralph Hames of Cornell University told BBC News

    Online.

    Egg laying

    Pollution in the form of acid rain causes a number of effects ontrees - from the loss of pine needles and leaves, to their complete

    destruction.

    The implications for birds include fewer insects to eat, more danger

    from predators and changes to nesting and roosting habits.

    A decline in forest food such as snail shells and earthworms may

    also lead to a deficiency of calcium, which the birds need to lay

    eggs.

    It is difficult to put a number on how serious a threat acid rain is t othe wood thrush, says Dr Hames.

    "This is far from the only threat against the bird," he says.

    The research is published in the journal Proceedings of the NationalAcademy of Sciences of the USA (PNAS).

    News ofAci rain

    One-thir of China hurt by aci rain

    By Joe Mcdonald, Associated Press

    BEIJING One-third of China's vastlandmass is suffering from acid rain caused by its rapidindustrial growth, while localleaders are failing to enforce environmental standards for fear of hurtingbusiness, said officials quoted Sunday by state media.

    China's factories spewed out 25.5 million tons of sulphur dioxide the chemicalthat causes acid rainlast year, up 27% from 2000, said Sheng Huaren, deputy chairman ofthe Standing Committee of

    parliament.

    Sheng released a report Saturday that found pollution from factories and power plants was rising by9% a year an embarrassment for a governmentthat promised this yearto clean up China's air. The

    report said sulphur dioxide emissions were double safe levels.

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    "Increased sulphur dioxide emissions meantthat one-third of China's territory was affected by acidrain, posing a majorthreatto soil and food safety," Sheng said, according to the Xinhua News Agencyand newspapers.

    Environmental protection has become a prominentissue in China following a string ofindustrial

    accidents that poisoned major rivers, forcing several cities to shut down their water systems.

    Chinese cities are among the world's smoggiest following two decades of breakneck economicgrowth. The government says all of China's major rivers are dangerously polluted. Millions of people

    lack access to clean drinking water.

    On Sunday, local officials said a tanker carrying 25 tons of caustic soda had fallen Friday into theXuefeng Riverin China's northwest, poisoning a drinking water source for 100,000 people.

    One person was killed in the accident, Xinhua said. Officials said the water quality had returned tonormal by Sunday afterthe government dumped 10 tons of hydrochloric acid into the waterto

    neutralize the caustic soda, also known as sodium hydroxide.

    Premier Wen Jiabao publicly criticized officials in April afterthe government revealed it failed to

    meet most ofits targets overthe past five years in environmental areas ranging from containingpollution to stopping the loss of farmland. Wen said officials would be held personally responsible for

    future environmental disasters.

    The government pledged this yearto cut air pollution emissions by 10% by 2010.

    Beijing plans to spend $175 billion on environmental protection overthe next five years, up 60% fromthe previous five years, according to Mao Rupai, chairman ofthe parliament's environmentalcommittee.

    Lawmakers are considering raising fines for environmental violators in orderto encourage companiesto spend more on clean technology, Mao said at a news conference on Saturday.

    Mao complained thatlocal officials failto enforce standards for fear of hurting businesses. He said

    some areas comply with as few as 30% of environmental regulations.

    "Itis true thatin some areas, local governments focus more on economic developmentthan on theenvironment," he said. "In the future, officials will be judged not just by their economic growth but byenvironmental protection as well."

    From the Sun ay times

    November 13, 2005

    Wil life reclaims lan hit by aci rain

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    Brown trout, prized among anglers, were particularly hard hit. When water gets acidic, their gills

    struggle to take in oxygen and their eggs are damaged so that many trout are stillborn, said Battarbee.

    By the 1980s the destruction was so bad thatit was souring international relations. The Scandinavian

    countries, for example, branded Britain the dirty man of Europe and suggested the UKs lax

    pollution controls were to blame forthe destruction oftheir conifer forests.

    Eventually a number ofinternational agreements were signed that forced governments to clean up

    theirindustries, with power stations and other heavy users of fossil fuels becoming obliged to install

    pollution control systems.

    As a result, the 3m tons of sulphur dioxide that were being pumped into the air annually by British

    industry in the 1970s has been cut by more than 80%.

    Battarbee said that despite such successes there were still problems, including continuing high

    emissions of oxides of nitrogen. He described these as a potentialtimebomb for future years.

    Such chemicals can both acidify rivers and raise the levels of certain plant nutrients such as nitrates,

    potentially prompting uncontrolled choking growth of algae and water weeds.

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    '

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    http://www.usatoday.com/tech/science/discoveries/china-acid-rain.htm

    http://www.timesonline.co.uk/tol/news/uk/article589692.ece