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
2013-11-25
15
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.
In what way can natural pollutants play an important role in controlling air pollution?
选项
A、They function as part of a purification process.
B、They are dwarfed by the pollutants produced by human activities.
C、They are less harmful to living beings than are other pollutants.
D、They have existed since the Earth developed.
答案
A
解析
第二段第二、三句提到:“随着地球的变化发展,这些污染物的浓度经过各种各样的化学反应发生变化,它们成为生物地球化学循环的组成部分。这些循环作为一种空气净化方案,可以使那些混合物从空气中转移到水或者土壤中。”可见,大自然排放出的这些混合物是地球自我净化循环的一部分,答案为A。
转载请注明原文地址:https://kaotiyun.com/show/HrS7777K
0
大学英语四级
相关试题推荐
Wegenerallyviewthefamilyasbeingoneofourmoststableinstitutions;yet,ourfamilysystemhas【B1】______anumberofchang
A、Toobservepeople’sattitudetowardsstrangers.B、Toseehowpeoplegetalongwiththeirfriends.C、Totestpeople’sbehavior
StudentsRunninganOnlineShop1.现在不少大学生在网上开店2.对此有人支持,有人反对3.你的看法
SocialmediapresentschallengetouniversitiesUniversitieshaveanewweaponinthebattletoprotecttheirreputations:thef
SocialmediapresentschallengetouniversitiesUniversitieshaveanewweaponinthebattletoprotecttheirreputations:thef
Evenintelligentlifeonearthcouldn’tsendradiowaveshalfacenturyago.Soitwouldbeimpossibleforanyintelligentbeing
Evenintelligentlifeonearthcouldn’tsendradiowaveshalfacenturyago.Soitwouldbeimpossibleforanyintelligentbeing
Inthepast,Americanfamiliestendedtohequitelarge.Parentsraisingfiveormorechildrenwerecommon.Overtheyears,the
Inthepast,Americanfamiliestendedtohequitelarge.Parentsraisingfiveormorechildrenwerecommon.Overtheyears,the
Humansaresocialanimals,andmostofustreasureourrelationshipswithfamilyandfriends.An【B1】_____lineofresearchsugges
随机试题
腹白线
同其他品牌相比,我们的电脑质量上乘,价格富有竞争力。
不属于丙酮酸酵解终产物的是
日常上楼的MET为
患者。女,30岁。食少难消,脘腹痞闷。大便溏薄,倦怠乏力,苔腻微黄,脉象虚弱者,治宜选用
根据《建设工程质量管理条例》规定,下列有关建设工程质量保修的说法中,正确的是()。
二级抗震设防钢筋混凝土墙,关于其厚度的说法,正确的有()。
对股权投资基金管理人进行登记、备案的作用是()。Ⅰ.加强机构自身合规运作和信息披露的意识Ⅱ.投资者可以通过中国基金业协会获悉管理人及基金的基本信息Ⅲ.中国基金业协会可以对以私募为名进行的公募、内幕交易、非法集资等非法活动加强自律管
某县摩托车厂为增值税一般纳税人,2017年11月份的业务情况如下:(1)销售给特约经销商A型号摩托车50辆,出厂不含税价每辆15000元,另收取包装费和售后服务费每辆1000元。该经销商当月只付清了其中30辆的购车款及价外费用,其余20辆承诺为厂家代销
简述相邻关系的概念及其法律特征。
最新回复
(
0
)