4、The dark smoke that comes out of stacks (大烟囱) or from a burning dump (垃圾) contains tiny bits of solid or liquid matter. The smoke also contains many gases, most of which cannot be seen. Altogether, they make up the serious problems of air pollution. In so many places it keeps us from seeing the sun, irritate (刺痛) our eyes, causes us to cough and makes us ill.
Air pollution can spread from city to city. It even spreads from one country to another. Some northern European countries have had "black snow" from pollutants that have traveled through the air from other countries and have fallen with the snow. So air pollution is a global problem. It can kill babies, older people and those who have respiratory (呼吸) disease. In 1952, four thousands people die in one week as a result of a serious air pollution breakout in London. In 1948 in a small town of Pennsylvania, 20 people died in a four - day period of air pollution. As often found in cities, air pollution increases the risks of lung disease, such as bronchitis and asthma. Of course, smoking and other factors help to cause these illnesses, too, but these causes have increased greatly during recent years as air pollution has become worse.