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  3. The Killer Smog Cases of Killer Smogs On the night of December 1st, 1930, a dense fog moved over the Meuse Valley, in Be

The Killer Smog Cases of Killer Smogs On the night of December 1st, 1930, a dense fog moved over the Meuse Valley, in Be

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问题                            The Killer Smog
    Cases of Killer Smogs
    On the night of December 1st, 1930, a dense fog moved over the Meuse Valley, in Belgium. Many factories in the valley poured smoke and fumes into the foggy air. This created dark smog of smoke and fog combined. People in the valley began to cough and strain for breath. The smog remained for four days. During that time, thousands of people became ill. The hospitals were filled with patients. Sixty people died. Most of them were older persons with heart and lung problems. Finally, a heavy rain washed away the smog. Scientists studied the causes of the disaster. They concluded that the illnesses and deaths were caused by chemicals in the smog.
    The first reported event of this kind in the United States happened in Donora, a factory town in a valley near Pittsburgh. In 1948, a killer smog made half of the population sick; there were 17 deaths. Again, older people with lung or heart diseases were hit hardest.
    London, England, has always been known for its "black fogs". In the winter of 1952, a milky white fog rolled into the city. It soon turned into black smog as the smoke of the city poured into the air. It was so hard to see that people had to walk in front of the buses to guide them. In this way, the most serious air pollution disaster in history began. When it was over, more than 4,000 people had been killed by the thick black smog.
    New York City has had several types of smogs since 1950. Each time, there were from 100 to 400 deaths caused by the smog. Although these smogs were not as deadly as London’s, New York City has the worst air pollution problem in the United States.
    Causes of Killer Smogs
    In all the killer smogs, factories and homes poured smoke and fumes into the air from the furnaces. The chemical fumes combined with the water droplets in the fog to form harmful substances. These substances caused the illness of those who breathed the polluted air.
    Usually, such harmful fumes rise into the upper air and are blown away by the wind. But sometimes there is an unusual weather condition called a temperature inversion. A layer of cold air remains near the ground as smoke and fumes pour into it. This is covered by an upper layer of warm air that acts like a lid. It prevents the polluted cooler air from rising. The harmful fumes pile up and make people ill. These fumes contain sulfur dioxide, soot particles, and other chemicals. The smog may be so thick that airports are closed and chains of collisions occur on the highways.
    Another type of smog occurs in Los Angeles. Here the weather may be clear and sunny. But stinging eyes and dry coughs show that harmful chemicals fill the air. The smog is due to invisible gases, mostly from automobile exhausts. Because these chemicals are changed by the sun high up in the air, Los Angeles smog is called photochemical smog. It contains automobile exhaust fumes and nitrogen oxides changed by the sun’s rays. Added to these are sulfur dioxide and other fumes from factories and oil refineries. Photochemical smog is found in many large cities all over the world.
    Harmful Substances Found in Smogs
    Killer smogs don’t happen very often, fortunately. But in many large cities, a combination of automobile exhaust fumes, home furnace smoke, and factory waste gases pours into the air. This may also happen in the suburbs, or out in the country, where large factories have been built. A number of harmful substances have been found in the air there. When these substances are breathed in day after day, the health of the population is affected.
    Sulfur dioxide is formed when fuels containing sulfur are burned. The sulfur combines with the oxygen in the air to form sulfur dioxide. This gas probably caused most of the deaths in the killer smogs. It combines with the water droplets in the air, or with the mucus(黏液)in the respiratory system. This can form sulfuric acid. Experiments with animals show that sulfur dioxide can paralyze or destroy the cilia in the air passages. It damages the lungs and lowers the resistance to pneumonia and influenza. It can also cause bronchitis(支气管炎)and emphysema.
    Soot is the black or gray smoke coming from chimneys and smoke stacks. It consists of particles that float in the air and then settle to the ground. Cancer-producing chemicals have been found in soot. They are suspected of causing lung cancer, but proof is still lacking. Most cases of lung cancer are probably caused by smoking cigarettes. But it is known that populations living where there is severe air pollution have a higher rate of lung cancer than people who live where there is clean air. This is true, even if their smoking habits are the same.
    Carbon monoxide is produced by all automobile engines. Defective furnaces can also produce this gas. When carbon monoxide enters the lungs, it combines with the hemoglobin(血红蛋白)of the red blood cells. This prevents the red blood cells from carrying oxygen all over the body. Where there are traffic jams, carbon monoxide may pile up in the air. It can cause headaches and dizziness. Sometimes carbon monoxide can enter the body of a car because of a leak in the exhaust system. In such cases it can cause serious illness or even death.
    Measures Taken to Deal With the Problem
    Soot and fumes produced by furnaces can be removed by several methods. Scrubbing sprays of water can clean up the smoke. Another method uses high voltage electricity to chafe soot particles and to attract them to a charged plate.
    The automobile is now the chief cause of air pollution. This is the most serious problem in Los Angeles. The state of California requires air pollution controls on all new automobiles sold in that state. All new cars have valves to return unburned gases to the engine. In addition, it has been proposed that only lead-free gasoline should be used. But the exhaust fumes still contain nitrogen oxides, carbon monoxide, and other harmful substances.
    A federal law requires that, by 1975, new cars should have devices to get rid of almost all harmful fumes. Although much work has been done, such cars have not yet been perfected. Perhaps cars run by steam engines or by battery power may be the answer. Perhaps more people will have to use trains or buses to travel in the cities. The problem of air pollution is not easy to solve. But more will have to be done to prevent the poisoning of the air we all must breathe.
Carbon monoxide, combined with the hemoglobin, will prevent the red blood cells from carrying ______ all over the body.
选项
答案oxygen
解析 本题相应信息在文章倒数第四段第三句和第四句“When carbon monoxide … carrying oxygen all over the body．”
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