四六级

　　2019年下半年英语六级考试时间是12月14日，备考时间紧迫，小编为各位考生准备了六级模拟题，基础比较差的考生现在就可以看起来了，另外，英语六级模拟题下载可以到文都网校四六级频道。

　　完整版请下载:19年下半年英语六级阅读模拟题及下载（十四）

　　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.

　　答案：BEFNCMJDKH

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