Passage Two

　　Words: 1,103

　　How Ozone Pollution Works

　　A) The weather report on the radio or TV tells you that it is going to be sunny and hot and that an orange ozone alert has been issued. What is ozone? What does an orange alert mean? Why should you be concerned about it? In this article, we will examine what ozone is, how it is produced, what health hazards it poses and what you can do to reduce ozone pollution.

　　B) Ozone is a molecule of three oxygen atoms bound together (O3). It is unstable and highly reactive. Ozone is used as a bleach, a deodorizing agent, and a sterilization agent for air and drinking water. At low concentrations, it is toxic. Ozone is found naturally in small concentrations in the stratosphere, a layer of Earth’s upper atmosphere. In this upper atmosphere, ozone is made when ultraviolet light from the sun splits an oxygen molecule (O2), forming two single oxygen atoms. If a freed atom collides with an oxygen molecule, it becomes ozone. Stratospheric ozone has been called “good” ozone because it protects the Earth’s surface from dangerous ultraviolet light.

　　C) Ozone can also be found in the troposphere, the lowest layer of the atmosphere. Tropospheric ozone (often termed “ bad ” ozone) is man - made, a result of air pollution from internal combustion engines and power plants. Automobile exhaust and industrial emissions release a family of nitrogen oxide gases (NOx) and volatile organic compounds (VOC), by-products of burning gasoline and coal. NOx and VOC combine chemically with oxygen to form ozone during sunny, high- temperature conditions of late spring, summer and early fall. High levels of ozone are usually formed in the heat of the afternoon and early evening, dissipating during the cooler nights.

　　D) Although ozone pollution is formed mainly in urban and suburban areas, it ends up in rural areas as well, carried by prevailing winds or resulting from cars and trucks that travel into rural areas. Significant levels of ozone pollution can be detected in rural areas as far as 250 miles downwind from urban industrial zones.

　　E) You can make ozone test strips to detect and monitor ozone levels in your own backyard or around your school. You will need corn starch, filter paper (coffee filters work well) and potassium iodide (can be ordered from a science education supplier such as Carolina Biological Supply or Fisher Scientific). Basically, you make a paste from water, corn starch and potassium-iodide, and you paint this paste on strips of filter paper. You then expose the strips to the air for eight hours. Ozone in the air will react with the potassium iodide to change the color of the strip. You will also need to know the relative humidity, which you can get from a newspaper, weather broadcast or home weather station.

　　F) When you inhale ozone, it travels throughout your respiratory tract. Because ozone is very corrosive, it damages the bronchioles and alveoli in your lungs, air sacs that are important for gas exchange. Repeated exposure to ozone can inflame lung tissues and cause respiratory infections.

　　G) Ozone exposure can aggravate existing respiratory conditions such as asthma, reduce your lung function and capacity for exercise and cause chest pains and coughing. Young children, adults who are active outdoors and people with respiratory diseases are most susceptible to the high levels of ozone encountered during the summer. In addition to effects on humans, the corrosive nature of ozone can damage plants and trees. High levels of ozone can destroy agricultural crops and forest vegetation.

　　H) To protect yourself from ozone exposure, you should be aware of the Air Quality Index (AQI) in your area every day—you can usually find it in the newspaper or on a morning weather forecast on TV or radio. You should also be familiar with the U.S. Environmental Protection Agency (EPA) guide for ozone-alert values.

　　I) What do the numbers in the AQI mean? The AQI measures concentrations of five air pollutants: ozone, sulfur dioxide, particulate matter, carbon monoxide and nitrogen dioxide. The EPA has chosen these pollutants as criteria pollutants, but these are not all of the pollutants in the air. These concentrations are compared to a standard set out in federal law. An index value of 100 means that all of the criteria pollutants are at the maximum level that is considered safe for the majority of the population. To reduce your exposure to ozone, you should avoid exercising during afternoon and early evening hours in the summer.

　　J) There are several ways you can help to decrease ozone pollution. Limit using your automobile during afternoon and early evening hours in the late spring, summer and early fall. Do not use gasoline-powered lawn equipment during these times. Do not fuel your car during these times. Do not light fires or outdoor grills during these times. Keep the engine of your car or boat tuned. Make sure that your tires are properly inflated. Use environmentally safe paints, cleaning and office products (some of these chemicals are sources of VOC).

　　K) Besides personal attempts to reduce ozone pollution, the EPA has initiated more stringent air-quality standards (such as the Clean Air Act and its modifications) to reduce air pollution. Compliance with these standards by industries, manufacturers and state and local governments has significantly reduced the levels of many common air pollutants.

　　L) With continued conservation and reduction practices, adherence to ozone-pollution warnings, research and government regulation, ozone-pollution levels should

　　continue to fall. Perhaps future generations will not be threatened by this environmental pollutant.

　　M) The thing that determines whether ozone is good or bad is its location. Ozone is ‘‘good，，when it is in the stratosphere. The stratosphere is a layer of the atmosphere starting at the level of about 6 miles (about 10 kilometers) above sea level. The stratosphere naturally contains about six parts per million of ozone, and this ozone is very beneficial because it absorbs UV radiation and prevents it from reaching us.

　　N) Ozone is “bad” when it is at ground level. Ozone is a very reactive gas that is hard on lung tissue. It also damages plants and buildings. Any ozone at ground level is a problem. Unfortunately, chemicals in car exhaust and chemicals produced by some industries react with light to produce lots of ozone at ground level. In cities, the ozone level can rise to a point where it becomes hazardous to our health. That’s when you hear about an ozone warning on the news.

　　1. When ultraviolet rays from the sun separate an oxygen molecule into two single oxygen atoms in the stratosphere, the combination of a single oxygen atom and an oxygen molecule forms ozone.

　　2. You can make ozone test strips by yourself to find out about ozone levels in your own locale.

　　3. Long-time exposure to ozone is badly harmful to our respiratory system.

　　4. Chemicals in industrial waste gas and vehicle exhaust react with light to form lots of ozone at ground level.

　　5. Internal combustion engines and power plants cause the artificial tropospheric ozone, also known as “bad” ozone.

　　6. Ozone is very helpful because it absorbs UV radiation and separates us from it.

　　7. Using gasoline-powered lawn equipment in the late spring, summer and early fall may increase ozone pollution.

　　8. Ozone pollution occurs in urban and suburban areas as well as in rural areas.

　　9. In order to decrease ozone pollution, the EPA has set up more rigorous air-quality standards.

　　10. Pay close attention to the Air Quality Index in your area every day can keep you away from ozone exposure.

　　文章精要

　　文章主要介绍了什么是臭氧，臭氧污染的形成、危害，以及臭氧有利的一 面。文章还具体介绍了如何自己手工制作检测仪;如何避免暴露在臭氧之下;如 何预防和减少臭氧污染等。

　　答案解析

　　1. B 本题答案的信息来自B段的倒数第二、三句话。原文中提到太阳紫外线将 氧分子分成了两个单独的氧原子，氧原子与氧分子再结合就生成了臭氧。 题干正好表达了这个意思。ultraviolet rays即是原文中的ultraviolet light。

　　2. E 本题答案的信息来自E段第一句话。题目中的find out about意为“弄清有关 的情况”，和原文中的detect and monitor含义相对应;题目中的inyour own locale和原文中的in your own backyard相对应。

　　3. F 本题答案的信息来自F段。F段提到人吸入臭氧后，它可以贯穿你的呼吸系统。接着提到它可能损害细支气管、肺部等呼吸系统的部位，故可知长期 暴露在臭氧下有损呼吸系统。

　　4. N 本题答案的信息来自N段第五句话，题干是对本句的同义转述。

　　5. C 本题答案的信息来自C段的第二句话。原句中先说“果”后说“因”，题目将

　　“因”提前，然后说“果”;原文中的man-made与题干中的artificial相对应; 原文中的termed与题干中的known as相对应。

　　6. M 本题答案的信息来自M段第二句和最后一句话。原文中第二句话首先提到

　　Ozone is “good” when it is in the stratosphere.，在最后一句中提到臭氧为什 么有益;原文中的beneficial与题干中的helpfUl相对应;题目中的separates from对应原文中的prevents from。

　　7. J 本题答案的信息来自J段第一、二、三句话。原文中J段的首句提到有几种可以降低臭氧污染的方法，接下来提到的一种方法是Do not use gasoline- powered lawn equipment during these times.由此推测Using gasoline-powered lawn equipment会导致臭氧污染增加;而由第二句话可推测出原文中的 during these times指的是in the late spring, summer and early fall。

　　8. D 本题答案的信息来自D段第一句话。原文提到臭氧污染主要在城市和城市郊区出现，但因为风和汽车、卡车运输的作用，农村也会发生臭氧污染， 题干是对此的归纳。

　　9. K 本题答案的信息来自K段第一句话。原文中的initiated和题目中的set up属于同义转换;原文中的stringent替换为了rigorous;原文中的reduce ozone pollution替换为了decrease ozone pollution。

　　10. H本题答案的信息来自H段第一句话。题目中的keep you away from对应原文的protect yourself from;题目中的Pay close attention to 对应原文的should be aware of。

(责任编辑：田学江)