首页
登录
职称英语
A useful definition of an air pollutant is a compound added directly or indi
A useful definition of an air pollutant is a compound added directly or indi
游客
2023-07-07
24
管理
问题
A useful definition of an air pollutant is a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or material adversely(有害地). 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(悬殊的差别)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(水蒸气)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 concentrations(浓度)of these pollutants were altered by various chemical reactions; they became components in biogeochemical(生物地球化学的)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 this localized 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(有害的)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. [br] According to the passage, the numerical value of the concentration level of a substance is only useful if
选项
A、the other substances in the area are known
B、it is a localized area
C、it can be calculated quickly
D、the naturally occurring level is also known
答案
D
解析
原文提到:“事实上,数值能告诉我们的信息很少,除非我们知道这意味着比该区域自然产生的浓度增加了多少。”这与D项的表述吻合。
转载请注明原文地址:https://tihaiku.com/zcyy/2817423.html
相关试题推荐
Ausefuldefinitionofanairpollutantisacompoundaddeddirectlyorindi
Ausefuldefinitionofanairpollutantisacompoundaddeddirectlyorindi
Howusefularetheviewsofpublicschoolstudentsabouttheirteachers?
Howusefularetheviewsofpublicschoolstudentsabouttheirteachers?
Howusefularetheviewsofpublicschoolstudentsabouttheirteachers?
Howusefularetheviewsofpublicschoolstudentsabouttheirteachers?
[originaltext]Fearanditscompanionpainaretwoofthemostusefulthings
DefinitionsofObesityA)Howdoesonedefinewhenapers
DefinitionsofObesityA)Howdoesonedefinewhenapers
DefinitionsofObesityA)Howdoesonedefinewhenapers
随机试题
Areyoulivingyourlifetothefullest?Areyouhappywithwho,what,orwh
经济风险分析应采用定性与定量相结合的方法,分析风险因素发生的可能性及给项目带来经
依据标准GB/T11457-2006《信息技术软件工程术语》,()是忽
对某土体进行室内压缩试验,当法向应力p1=100kPa时,测得孔隙比e1=0.6
A.Ⅰ期临床试验 B.Ⅱ期临床试验 C.Ⅲ期临床试验 D.Ⅳ期临床试验
已知函数f(x,y)在点(0,0)的某个邻域内连续,且 A.点(0,0)不是f
意识可以被看成是( )状态下的觉知A.觉醒 B.朦胧 C.睡眠 D.激奋
男性,60岁。腹痛,为阵发性绞痛,频繁呕吐.停止排便、排气8小时。两年前因十二指
()的收购方式又被称为换股。A:用现金购买股票 B:用股票购买资产 C:用股
变异系数又称离散系数,是用标准差除以( )得到的相对数,它表示数据的相对离散波动
最新回复
(
0
)