Acid Rain.

« the Adirondack Mountains of New York State, a quarter of the lakes and ponds are acidic, and many have lost their brook trout and other fish.

In the middleAppalachian Mountains, over 1,300 streams are afflicted.

All of Norway’s major rivers have been damaged by acid rain, severely reducing salmon and trout populations. E Plants and Animals The effects of acid rain on wildlife can be far-reaching.

If a population of one plant or animal is adversely affected by acid rain, animals that feed on that organism mayalso suffer.

Ultimately, an entire ecosystem may become endangered.

Some species that live in water are very sensitive to acidity, some less so.

Freshwater clams andmayfly young, for instance, begin dying when the water pH reaches 6.0.

Frogs can generally survive more acidic water, but if their supply of mayflies is destroyed byacid rain, frog populations may also decline.

Fish eggs of most species stop hatching at a pH of 5.0.

Below a pH of 4.5, water is nearly sterile, unable to support anywildlife. Land animals dependent on aquatic organisms are also affected.

Scientists have found that populations of snails living in or near water polluted by acid rain are decliningin some regions.

In The Netherlands songbirds are finding fewer snails to eat.

The eggs these birds lay have weakened shells because the birds are receiving lesscalcium from snail shells. F Human-Made Structures Acid rain and the dry deposition of acidic particles damage buildings, statues, automobiles, and other structures made of stone, metal, or any other material exposed toweather for long periods.

The corrosive damage can be expensive and, in cities with very historic buildings, tragic.

Both the Parthenon in Athens, Greece, and the TajMahal in Agra, India, are deteriorating due to acid pollution. G Human Health The acidification of surface waters causes little direct harm to people.

It is safe to swim in even the most acidified lakes.

However, toxic substances leached from soil canpollute local water supplies.

In Sweden, as many as 10,000 lakes have been polluted by mercury released from soils damaged by acid rain, and residents have beenwarned to avoid eating fish caught in these lakes.

In the air, acids join with other chemicals to produce urban smog, which can irritate the lungs and make breathingdifficult, especially for people who already have asthma, bronchitis, or other respiratory diseases.

Solid particles of sulfates, a class of minerals derived from sulfurdioxide, are thought to be especially damaging to the lungs. H Acid Rain and Global Warming Acid pollution has one surprising effect that may be beneficial.

Sulfates in the upper atmosphere reflect some sunlight out into space, and thus tend to slow down globalwarming.

Scientists believe that acid pollution may have delayed the onset of warming by several decades in the middle of the 20th century. IV EFFORTS TO CONTROL ACID RAIN Acid rain can best be curtailed by reducing the amount of sulfur dioxide and nitrogen oxides released by power plants, motorized vehicles, and factories.

The simplestway to cut these emissions is to use less energy from fossil fuels.

Individuals can help.

Every time a consumer buys an energy-efficient appliance, adds insulation to ahouse, or takes a bus to work, he or she conserves energy and, as a result, fights acid rain. Another way to cut emissions of sulfur dioxide and nitrogen oxides is by switching to cleaner-burning fuels.

For instance, coal can be high or low in sulfur, and some coalcontains sulfur in a form that can be washed out easily before burning.

By using more of the low-sulfur or cleanable types of coal, electric utility companies and otherindustries can pollute less.

The gasoline and diesel oil that run most motor vehicles can also be formulated to burn more cleanly, producing less nitrogen oxide pollution.Clean-burning fuels such as natural gas are being used increasingly in vehicles.

Natural gas contains almost no sulfur and produces very low nitrogen oxides.Unfortunately, natural gas and the less-polluting coals tend to be more expensive, placing them out of the reach of nations that are struggling economically. Pollution can also be reduced at the moment the fuel is burned.

Several new kinds of burners and boilers alter the burning process to produce less nitrogen oxides andmore free nitrogen, which is harmless.

Limestone or sandstone added to the combustion chamber can capture some of the sulfur released by burning coal. Once sulfur dioxide and oxides of nitrogen have been formed, there is one more chance to keep them out of the atmosphere.

In smokestacks, devices called scrubbersspray a mixture of water and powdered limestone into the waste gases (flue gases), recapturing the sulfur.

Pollutants can also be removed by catalytic converters.

In aconverter, waste gases pass over small beads coated with metals.

These metals promote chemical reactions that change harmful substances to less harmful ones.

Inthe United States and Canada, these devices are required in cars, but they are not often used in smokestacks. Once acid rain has occurred, a few techniques can limit environmental damage.

In a process known as liming, powdered limestone can be added to water or soil toneutralize the acid dropping from the sky.

In Norway and Sweden, nations much afflicted with acid rain, lakes are commonly treated this way.

Rural water companiesmay need to lime their reservoirs so that acid does not eat away water pipes.

In cities, exposed surfaces vulnerable to acid rain destruction can be coated with acid-resistant paints.

Delicate objects like statues can be sheltered indoors in climate-controlled rooms. Cleaning up sulfur dioxide and nitrogen oxides will reduce not only acid rain but also smog, which will make the air look clearer.

Based on a study of the value thatvisitors to national parks place on clear scenic vistas, the U.S.

Environmental Protection Agency thinks that improving the vistas in eastern national parks alone will beworth $1 billion in tourist revenue a year. A National Legislation In the United States, legislative efforts to control sulfur dioxide and nitrogen oxides began with passage of the Clean Air Act of 1970.

This act established emissionsstandards for pollutants from automobiles and industry.

In 1990 Congress approved a set of amendments to the act that impose stricter limits on pollution emissions,particularly pollutants that cause acid rain.

These amendments aim to cut the national output of sulfur dioxide from 23.5 million tons to 16 million tons by the year2010.

Although no national target is set for nitrogen oxides, the amendments require that power plants, which emit about one-third of all nitrogen oxides released tothe atmosphere, reduce their emissions from 7.5 million tons to 5 million tons by 2010.

These rules were applied first to selected large power plants in Eastern andMidwestern states.

In the year 2000, smaller, cleaner power plants across the country came under the law. These 1990 amendments include a novel provision for sulfur dioxide control.

Each year the government gives companies permits to release a specified number of tonsof sulfur dioxide.

Polluters are allowed to buy and sell their emissions permits.

For instance, a company can choose to reduce its sulfur dioxide emissions more than thelaw requires and sell its unused pollution emission allowance to another company that is further from meeting emission goals; the buyer may then pollute above the. »