托福阅读真题Official 48 Passage 3（七）

托福阅读真题Official 48 Passage 3（七）

Climate and Urban Development

For more than a hundred years,it has been known that cities are generally warmer than surrounding rural areas.This region of city warmth,known as the urban heat island,can influence the concentration of air pollution.However,before we look at its influence,let’s see how the heat island actually forms.

The urban heat island is due to industrial and urban development.In rural areas,a large part of the incoming solar energy is used in evaporating water from vegetation and soil.In cities,where less vegetation and exposed soil exist,the majority of the Sun’s energy is absorbed by urban structures and asphalt.Hence,during warm daylight hours,less evaporative cooling in cities allows surface temperatures to rise higher than in rural areas.The cause of the urban heat island is quite involved.Depending on the location,time of year,and time of day,any or all of the following differences between cities and their surroundings can be important:albedo(reflectivity of the surface),surface roughness,emissions of heat,emissions of moisture,and emissions of particles that affect net radiation and the growth of cloud droplets.

At night,the solar energy(stored as vast quantities of heat in city buildings and roads)is slowly released into the city air.Additional city heat is given off at night(and during the day)by vehicles and factories,as well as by industrial and domestic heating and cooling units.The release of heat energy is retarded by the tall vertical city walls that do not allow infrared radiation to escape as readily as does the relatively level surface of the surrounding countryside.The slow release of heat tends to keep nighttime city temperatures higher than those of the faster-cooling rural areas.Overall,the heat island is strongest(1)at night when compensating sunlight is absent;(2)during the winter,when nights are longer and there is more heat generated in the city;and(3)when the region is dominated by a high-pressure air pressure(atmospheric pressure)is the pressure exerted by the mass of air above a given place area with light winds,clear skies,and less humid air.Over time,increasing urban heat islands affect climatological temperature records,producing artificial warming in climatic records taken in cities.This warming,therefore,must be accounted for in interpreting climate change over the past century.

The constant outpouring of pollutants into the environment may influence the climate of the city.Certain particles reflect solar radiation,thereby reducing the sunlight that reaches the surface.Some particles serve as nuclei upon which water and ice form.Water vapor condenses onto these particles when the relative humidity is as low as 70 percent,forming haze that greatly reduces visibility.Moreover,the added nuclei increase the frequency of city fog.

Studies suggest that precipitation may be greater in cities than in the surrounding countryside;this phenomenon may be due in part to the increased roughness of city terrain,brought on by large structures that cause surface air to slow and gradually converge.This piling up of air over the city then slowly rises,much like toothpaste does when its tube is squeezed.At the same time,city heat warms the surface air,making it more unstable,which enhances rising air motions,which,in turn,aids in forming clouds and thunderstorms.This process helps explain why both tend to be more frequent over cities.

On clear still nights when the heat island is pronounced,a small thermal low-pressure area forms over the city.Sometimes a light breeze—called a country breeze—blows from the countryside into the city.If there are major industrial areas along the outskirts,pollutants are carried into the heart of town,where they tend to concentrate.Such an event is especially probable if vertical mixing and dispersion of pollutants are inhibited.Pollutants from urban areas may even affect the weather downwind from them.

Question 13 of 14

Look at the four squares[■]that indicate where the following sentence could be added to the passage.The resulting difference in atmospheric pressure between the city and the countryside can cause air to shift.Where would the sentence best fit?Click on a square[■]to add the sentence to the passage.

正确答案：A

题目详解

题型分类：插入句子题

题干分析：考察句子和句子之间的衔接判断黑体句的意思是，城市和乡村大气压强的不同会导致空气流动。逻辑暗示是因果，前方信息应该是气压的不同，后面就应该是空气的流动这一信息的展开。

选项分析：

A选项方块后就是产生风的描述，紧随黑体句语义。

B选项前面没有气压，后面没有空气流动，错误。

C选项such an event指代前面内容，不可以插入句子使文章断裂。

D选项方块前后描述的都是pollution的特点，没有气压和空气流动，错误。

Question 14 of 14

Directions:An introductory sentence for a brief summary of the passage is provided below.Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage.Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage.This question is worth 2 points.

Cities are generally warmer than the surrounding countryside,a phenomenon known as the urban heat island.

Answer Choices:

A.

In the countryside,much solar energy is used in evaporation,but in the city this energy builds up as heat.

B.

The urban heat island is strongest in the summer,when the days are long and the sunlight is intense.

C.

Increased industrial and urban development has also increased average levels of humidity over the last century.

D.

Heat and air are trapped in the irregular spaces between buildings,which creates the atmospheric conditions that result in storms and winds.

E.

Pollution from cars and factories helps increase the amounts of fog and precipitation that occur in cities.

F.

Country breezes blow pollutants out from the cities into the surrounding countryside.

正确答案：ADE

题目详解

题型分类：文章总结题

题干分析：选择概括性的正确选项

选项分析：

A选项：定位到文章的第二段，主要讲的是城市和乡村之间热量的不同，突出城市热量的高，正确。

D选项：可以定位到文章中的第五段后半部分，making it more unstable,which enhances risings air motions,which,in turn,aids in forming clouds and thunderstorms.因此该选项正确。

E选项：汽车和工厂污染物会导致大雾和降雨，可以定位到文章中的第四段，正确。

B选项：The urban heat island is strongest in the summer...可以定位到文章的第四段，该选项并不包含在其中，因此错误。

C选项：并未提及工业和城市发展与湿度增加的关系，错误。

F选项：风吹反了，原文中说的是从乡村吹到城市，另外它也是个无关项。

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