4-13 都市杀手（在线收听）

Big City Killer

If the cigarettes don't get¹ you the traffic pollution will. Up to a fifth of all lung cancer deaths in cities are caused by tiny particles of pollution, most of them from vehicle exhausts.

That's the conclusion of the biggest study into city pollution to date, which tracked² half a million Americans for 16 years. It suggests the impact is far greater than feared.

The study is important because it followed individuals, says British expert Roy Harrison of the University of Birmingham, allowing the researchers to separate the effects of smoking and pollution. “In the past, we have often just compared urban areas and rural areas. But more people smoke in cities, and it is difficult to compensate³ for that.”

The research focused on particles less than 2.5 micrometres in diameter, known as PM2.5s. These fine particles are thought to kill by lodging⁴ deep in the lungs. The researchers found that the long-term death rate from lung cancer rose by 8 per cent for every 10-microgram increase in the average concentration⁵ of PM2.5s per cubic metre. The increased risk is comparable with the risks to long? term passive smokers.

Typical PM2.5 levels in the US are 20 micrograms in Los Angeles and 16 micrograms in New York--the limit set in 1997 by the Environmental Protection Agency is 15 micrograms. British levels are similar, though one PM2.5 monitor at Marylebone Road in London records an average of 32 micrograms. “I'd say London has a special problem because of the high proportion of diesel⁶ fumes⁷,” says George Thurston of New York University, co-leader of the study.

The implications⁸ are bleakest⁹ for developing countries. In heavily polluted cities such as Delhi, particle levels average over 300 micrograms and most of this is probably PM2.5s.

注释：

1.get [get] vt.〈口〉击中；杀死；毁坏

2.track [trAk] vt. 追踪，跟踪

3.compensate [5kCmpEnseit] vi. 抵消；弥补

4.lodge [lCdV] vi. 埋入，嵌入；留存

5.concentration [7kCnsen5treiFEn] n. 浓度；浓缩

6.diesel [5di:zEl] a. 柴油机的  　

7.fume [fju:m] n. [常作～s]（有害、难闻、浓烈的）烟、气、汽

8.implication [7impli5keiFEn] n. 含意；密切关系

9.bleak [bli:k] a. 冷酷的；严峻的

都市杀手

如果香烟没有置你于死地的话，那么交通污染将成为你的杀手。城市里1/5的肺癌死亡病例都是由细微污染颗粒物所致，而颗粒物的主要来源就是机动车排放的废气。

　　这是迄今为止一项规模最大的关于城市污染的研究所得出的结论。这项研究长达16年，对50万美国人进行了跟踪调查。研究表明，交通污染影响的严重性远远超过人们的担忧。

　　伯明翰大学的英国专家罗伊•哈里森说，此项研究非常重要，因为它是个人追踪，使研究者得以将吸烟的影响与污染的影响区分开来。他说：“过去，我们经常只是对比城市与乡村。但是由于城市的吸烟者比例大于乡村，所以研究很难对污染做出准确的判断。”

　　本项研究的重点是所谓的PM2.5，即直径小于2.5微米的微粒。研究人员认为，这些微粒通过积存在人体肺部而导致人的死亡。他们发现，每立方米PM2.5的平均浓度每增加10微克，在长期的作用之下，肺癌导致的死亡率就会增加8％。微粒污染所增加的危险与长期被动吸烟的危险是不相上下的。

　　在美国，PM2.5值在洛杉矶一般为20微克，在纽约为16微克——而1997年美国环境保护署规定的限制为15微克。英国的PM2.5值与美国类似，虽然在伦敦玛丽莱蓬大街的一台PM2.5监视仪记录的平均值为32微克。本项研究的领导人之一、纽约大学的乔治•瑟斯顿说：“我认为伦敦有一个特殊的问题，因为那里柴油排气的比例较高。”

　　对于发展中国家来讲，研究的结果令人不寒而栗。在那些污染严重的城市，如德里，微粒含量平均值超过了300微克，其中大多数可能都是PM2.5。