An air pollutnt 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 subtances 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 notrigen 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 as 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 subtance to be a pollutant; in fact, the numerial value tells us little until we know how much of an increase this represents over ther 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.
The word “adversely” in the first paragraph is closet in meaning to ________.
A. negatively
B. quickly
C. admittedly
D. considerably
Đáp án A.
Key words: paragraph 1, adversely
Clue: “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”: Ô nhiễm không khí được định nghĩa như hợp chất thải trực tiếp hoặc gián tiếp bởi con người vào không khí với một lượng để ảnh hưởng tiêu cực đến con người, động vật, thảm thực vật hoặc nguyên liệu.
adversely (adv) = in a way that is negative and unpleasant and not likely to produce a good result.
Vậy adversely gần nghĩa nhất với A. negatively: một cách tiêu cực.
Các đáp án còn lại là sai:
B. quickly: nhanh chóng
C. admittedly: được thừa nhận
D. considerably: đáng kể