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  3. ACID RAIN: What’s the Solution? One of the wildest regions in the U.S., far from civilization, is the Adirondack area of nor

ACID RAIN: What’s the Solution? One of the wildest regions in the U.S., far from civilization, is the Adirondack area of nor

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问题                      ACID RAIN: What’s the Solution?
    One of the wildest regions in the U.S., far from civilization, is the Adirondack area of northern New York State. For years this isolated spot has had the reputation of being one of best fishing spots in the U.S.
    As a boy 30 years ago, Bill Marleau first through the Adirondack wilderness near his small cabin on Woods Lake. Thousands of sportsmen have stayed at his father’s lodge nearby.
    But now Bill’s 134 hectares (335 acres) of lakefront land have only scenic value. Gone are those huge trout that used to swim in the turbulent, nutrientrich water a short distance from his doorstep. Gone from the cool nights are the sounds of thousands of frogs and toads.
    And gone are the birds that once fed on those water creatures.
    Occasionally Bill sees a lone fisherman fruitlessly cast his bait into the empty waters of old lake. "I just don’t have the heart to tell," he said. "This old lake’s dead. It was killed years ago by acid rain." What is acid rain?
    Acid rain is a popular term for precipitation in the form of rain, sleet, snow or hail that is more acidic than normal. Acid rain is produced when atmospheric moisture combines with pollutants from power plants, factories and automobiles.
    When fossil fuels such as coal and oil are burned, sulfur dioxide and nitrogen dioxide are produced. These two gases react with the water and oxygen in the atmosphere to form droplets of weak sulfur and nitric acid.
    Carried by prevailing winds and weather conditions, clouds containing these droplets travel hundreds, sometimes thousands, of kilometers from the source of the pollutants. Recently scientists found that acid rain now affects huge areas of the North Hemisphere.
    Power plants and factories in the heavily industrialized regions of Ohio and Indiana are believed to be the source of the acid rain that killed Woods Lake along with hundreds of others in New York State and eastern Canada. Acid haze over Alaska is believed to come all the way from Japan. And precipitation as acid as vinegar that falls on Scotland and Scandinavia probably originates in England.
    How Acidity Is Measured
    Scientists measure the acidity of rain in pH units. A pH scale from 0 to 14 is used. Depending upon its chemical composition, a solution is either acidic, alkaline (basic), or neutral. Distilled water, which has a pH of 7, is neutral. Substance with pH values less than 7 are acidic, while those over 7 are alkaline.
    Normal rain water with a pH of 5.6 is slightly acidic. But after reacting with industrial pollutants, particularly sulfur dioxide, the pH of rain quickly drops.
    When acid rain falls to Earth, much of it ends up in lakes and ponds. In addition to failing directly into a lake, acid rains runs off land into streams and rivers that eventually flow into lakes and ponds. Once acid rain gets into them, its effects can be deadly.
    Studies started in 1975 in the Adirondacks indicate that salamanders and frogs are the first to die when the pH is lowered. Normally the pH of a lake is 8,0 slightly alkaline. When the pH drops to 7, the eggs of salamanders and frogs fail to hatch. At pH 6.6 snails begin to die.
    Bacteria that decompose leaf matter die too, and the leaf matter collects on the lake bottom. As the acidity continues to drop, ail the major food chains in the lake become affected. In time all the fish die.
    Eventually primitive, oxygenconsuming plants nearly choke out all other aquatic greenery. Algae and fungal growth that thrive in an acidic environment move in and cover the entire bottom of the now destroyed lake.
    Looking like blue vinegar, the lake is now an entirely changed ecosystem. It contains no life expect the fungal and algal growth and a few surfacedwelling water bugs.
    Acid rain also affects plants on land.
    The effects of acid rain on terrestrial vegetation are not as well documented or as clearly understood as its effects on lake. Experiments by Ellis B. Cowling of North Carolina State University, however, indicate that acid rain destroys the natural waxy coating on tree leaves and fruits. This destruction makes the plants more susceptible to disease.
    Acid Rain Increasing
    The acid rain problem seems to be getting worse. According to the Environmental Protection Agency, the amount of sulfur dioxide from power plants, autos, and factories is four times greater than it was 25 years ago. And federal airpollution regulations don’t seem to be helping as much as had been expected.
    One problem is that the Clean Air Act of 1977 established air pollution standard based on measurements made at ground level. Environmentalists claim that this action has encouraged polluters to spread airborne pollutants at higher elevation instead of eliminating them altogether. Tall smokestacks, often more than 100 stories tall, now spread sulfur dioxide close to watercarrying clouds.
    Power company officials stress, however, that the tall stacks significantly reduce air pollution in areas near the power plants. And the officials also point to cleanup currently underway in the industry to reduce the amount of pollutants.
    New, cleanerburning furnaces have been installed in recently constructed power plants. Scrubbers are also available that can be installed on industrial and power plant smokestacks. The scrubbers can remove up to 85 percent of the sulfur such as lowsulfur, liquid coal.
    What can be done about lakes that are already acidic? Acidity can be reduced by dropping tons of lime (an alkaline substance) into the lake water. However, this solution is very expensive. Less optimistic scientists are trying to breed acidtolerant fish. These, however measures at best. The solution to acid rain can only come about cooperation between industry, government, and scientists.
Scientists measure the acidity of rain in ______.
选项
答案pH units
解析 该题是问科学家如何测量雨水的酸度。我们可以由题干判断出应该在第二部分找答案，并定位在第二部分首段首句。
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