首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
A useful definition of an air pollutant is a compound added directly or indirectly by humans to the atmosphere in such quantitie
A useful definition of an air pollutant is a compound added directly or indirectly by humans to the atmosphere in such quantitie
admin
2014-12-26
49
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. 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 vapour might be considered an air pollutant under certain conditions.
Many of the more important air pollutants, such as sulphur oxides, carbon monoxide, and nitrogen oxides, are found in nature. As the earth developed, the concentrations of these pollutants were altered by various chemical reactions; they became components in biogeochemical cycles. These reactions 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 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, sulphur 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 passage mainly discusses______.
选项
A、how gas chemicals become air pollutants
B、how much damage air pollutants can cause
C、the definition of an air pollutant
D、the quantity of compounds added to the atmosphere
答案
A
解析
主旨题。本文首段给出了空气污染物的定义,第二段介绍了许多有害的化学物质.它们造成的污染大都是因人类活动产生,第三段解释化学物质如何成为空气污染物。相较其他选项,选项A概括性强。所以答案选A。
转载请注明原文地址:https://kaotiyun.com/show/oOm7777K
0
大学英语六级
相关试题推荐
A、Theytendtobemoreintroverted.B、Theyaremorelikelytopursueperfection.C、Theyaremoreopentonewexperiences.D、They
RainforestCityA)Apatchoftropicalrainforesthastwicethenumberofmammalspecies,fivetimesthebatsandbirdsandtent
RainforestCityA)Apatchoftropicalrainforesthastwicethenumberofmammalspecies,fivetimesthebatsandbirdsandtent
A、Thekidscouldn’thidethingsperfectly.B、Thehider’sbodylanguagetellsthelocationunconsciously.C、Thepressureforcedt
A、Wealwaysusebodylanguagetoexpressourfeelings.B、Bodylanguagecanbecontrolledbyemotions.C、Emotionswillbeexpress
A、Theshoppingcenterisfloodedwithpeople.B、Theywillcometothemallsomeotherday.C、Parkinginthiscityisahorrible
A、Hecandoeverythingwell.B、Heonlyknowssomethingwithoutmastering.C、Helikesdoinghousework.D、Heispopularinthenei
A、Piracyisaneasythingtocommit.B、Inventionusuallyneedsheavycost.C、Patentisusefulbutnotpractical.D、Inventionsar
A、Halfofthemethaneintheatmosphereisfromanimals.B、Methanehasbecomethechiefsourceofgreenhousegas.C、Consumerbeh
Inasense,thenewprotectionismisnotprotectionismatall,atleastnotinthe【C1】______senseoftheterm.Theoldprotectio
随机试题
安全没有保障,随时可能发生垮坝事故的尾矿库称为()。
A.过氧化物酶强阳性B.中性粒细胞碱性磷酸酶偏低C.非特异酯酶染色阳性,可被氟化钠抑制D.细胞内铁染色强阳性E.糖原染色阳性,呈块状或颗粒状以上细胞化学染色有助于诊断下列疾病的是
【2004年第147题】土的含水量ω的定义,下列何种说法是正确的?
医疗废物集中处置单位的贮存、处置设施,应当( )。
建设单位于2011年6月14日竣工验收合格,则建设单位应当在()前,将建设工程竣工验收报告和规划、公安消防、环保等部¨出具的认可文件或者准许使用文件,报建设行政主管部门或者其他有关部门备案。
用友报表系统中,()定义了报表数据之间的运算关系,可以实现报表系统从其他子系统取数的功能,所以必须定义它。
在对外货物贸易统计中所使用的价格是:()。
已经采用公允价值模式计量的投资性房地产,不得从公允价值计量模式转为成本计量模式。()
下列程序执行后的输出结果是______。 main() { char arr[2][4]; strcpy(arr,"she");strcpy(arr[1],"he"); arr[0][3]=’&’; printf("%s\n",arr); }
Theprimeministerinsistedthat____________(成立委员会)tolookintothematter.
最新回复
(
0
)