Air Pollution
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    The earth's atmosphere is polluted naturally by sandstorms and the dust and gases from volcanoes.But the most serious kind of air pollution comes from people.Factories,power stations,and vehicle exhausts pump harmful gases into the air,contributing to global warming,causing acid rain,and destroying the ozone layer.On a much smaller scale,air pollution causes all sorts of breathing problems.There are no simple solutions to air pollution,but people could reduce air pollution by saving energy and reducing harmful emissions from vehicle exhaust and power stations.

  When a volcano erupts,dust is blasted high above the troposphere and may take weeks to be carried around the world.It is above the weather zon,so cannot be washed out of the air by rain.It will eventually fall to the earth after a few years.

  Air pollution is at its worst over big cities where millions of people live,work,and travel about in cars,buses,and trucks.Factory chimneys can be fitted with devices to cut down air pollution,but this is expensive.If better public transport and cycle lanes were available in towns and cities,people would be less likely to use their cars,reducing the overall amount of pollution.

  Smoking cigarettes adds to the general levels of air pollution as well as damaging our health.Cigarette smoke contains chemicals that cancause cancer,a gas which stops oxygen being taken into the blood and a substance called nicotine which raises blood pressure and makes the heart beat faster.No-smoking areas cut down on this pollution and save nonsmokers breathing in other people's cigarette smoke.

Comprehension Questions

1.What are the major causes of the pollution of atmosphere?2.What problems will people meet after the earth's atmosphere is poluted?
3.Why do people think that air pollution in big cities is at its worst?
4.What chemicals are contained in cigarette smoke?

FROM  《寻找永远的绿色》 P22~P24
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