AN AIR POLLUTANT IS DEFINED AS A COMPOUND ADDED DIRECTLY OR...

EXERCISE 3

An air pollutant is defined as a compound added directly or indirectly by humans to the

atmosphere in such quantities as to affect humans, animals, vegetation, or

materials adversely. Air pollution requires a very flexible definition that permits continuous

change. When the first air pollution laws were established in England in the fourteenth century,

air pollutants were limited to compounds that could be seen or smelled - a far cry from the

extensive list of harmful substances known today. As technology has developed and knowledge

of the health aspects of various chemicals has increased, the list of air pollutants has

lengthened. In the future, even water vapor might be considered an air pollutant under certain

conditions.

Many of the more important air pollutants, such as sulfur oxides, carbon monoxide, and nitrogen

oxides, are found in nature. As the Earth developed, the concentration of these pollutants was

altered by various chemical reactions; they became components in biogeochemical

cycles. These serve as an air purification scheme by allowing the compounds to move from the

air to the water or soil. On a global basis, nature's output of these compounds dwarfs that

resulting from human activities.

However, human production usually occurs in a localized area, such as a city. In such a region,

human output may be dominant and may temporarily overload the natural purification scheme

of the cycles. The result is an increased concentration of noxious chemicals in the air. The

concentrations at which the adverse effects appear will be greater than the concentrations that

the pollutants would have in the absence of human activities. The actual concentration need not

be large for a substance to be a pollutant; in fact, the numerical value tells us little until we know

how much of an increase this represents over the concentration that would occur naturally in

the area. For example, sulfur dioxide has detectable health effects at 0.08 parts per million

(ppm), which is about 400 times its natural level. Carbon monoxide, however, has a natural

level of 0.1 ppm and is not usually a pollutant until its level reaches about 15 ppm.

Questions

Question 1: What does the passage mainly discuss?

A. The economic impact of air pollution.

B. What constitutes an air pollutant.

C. How much harm air pollutants can cause.

D. The effects of compounds added to the atmosphere.

Question 2: The word “adversely” in the first paragraph is closest in meaning to ...

A. negatively B. quickly C. admittedly D. considerably

Question 3: It can be inferred from the first paragraph that__________.

A. water vapor is an air pollutant in localized areas

B. most air pollutants today can be seen or smelled

C. the definition of air pollution will continue to change

D. a substance becomes an air pollutant only in cities

Question 4: The word “These” in the second paragraph is closest in meaning to__________.

A. the various chemical reactions

B. the pollutants from the developing Earth

C. the compounds moved to the water or soil

D. the components in biogeochemical cycles

Question 5: For which of the following reasons can natural pollutants play an important role in

controlling air pollution?

A. They function as part of a purification process.

B. They occur in greater quantities than other pollutants.

C. They are less harmful to living beings than other pollutants.

D. They have existed since the Earth developed.

Question 6: According to the passage, human-generated air pollution in localized

regions ...

A. can be dwarfed by nature's output of pollutants

B. can overwhelm the natural system that removes pollutants

C. will damage areas outside of the localized regions

D. will react harmfully with natural pollutants

Question 7: The word “localized” in the third paragraph is closest in meaning to ...

A. specified B. circled C. surrounded

D. encircled

Question 8: According to the passage, the numerical value of the concentration level of a

substance is only useful if ...

A. the other substances in the area are known B. it is in a localized area

C. the natural level is also known D. it can be calculated quickly

Question 9: The word “detectable” in the third paragraph is closest in meaning to ...

A. beneficial B. special C. measurable D. separable

Question 10: Which of the following is best supported by the passage?

A. To effectively control pollution, local government should regularly review their air pollution

laws.

B. One of the most important steps in preserving natural lands is to better enforce air pollution

C. Scientists should be consulted in order to establish uniform limits for all air pollutants.

D. Human activities have been effective in reducing air pollution.