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Vehicle pollution
　　
　　Cleaner than what?
　　
　　Why an electric car may be much dirtier than apetrol one.
　　
　　DRIVING an electric car confers a badge of greenery,or so the marketing departments of their makers would have you believe. Yet areport which analyses the life cycle of car emissions (ie, all the way fromthose created by the mining of materials for batteries, via the ones from theproduction of fuel and the generation of electricity, to the muck that actuallycomes out of the exhaust) presents a rather different picture. Abattery-powered car recharged with electricity generated by coal-fired power stations,it found, is likely to cause more than three times as many deaths frompollution as a conventional petrol-driven vehicle. Even a battery car runninn the average mix of electrical power generated in America is much morehazardous than the conventional alternative.
　　
　　相比于传统的汽车，驾驶一辆电动汽车被认为是清洁环保的，或者说电动汽车的制造商会以这样说辞来销售。然而，有一家报告分析了汽车排放物的整个周期，结果却不是人们所想的那样（整个过程包括从制造电池产生的污染，经过生产燃料、电能产生的污染到汽车尾气排出的废气）。电动汽车的充电需要火电厂发电提供电能，这种充电方式造成的污染致死人数是传统燃油汽车的三倍还多。在美国，即使电动汽车的电能不光是只有火电厂的混合供应,这也比传统燃油汽车的更加致命。
　　
　　Christopher Tessum, Jason Hill and Julian Marshallof the University of Minnesota have just published this study in theProceedings of the National Academy of Sciences. They estimate how levels offine particulate matter and ground-level ozone—two important constituents of air pollution, which kills more than100,000 people a year in America—would change if eachof 11 ways of powering a car were to be responsible for 10% of thevehicle-miles expected to be driven in America in 2020.
　　
　　来自明尼苏达大学的克里斯托弗特塞姆、杰森希尔和朱利安马绍尔将他们的研究发表在《美国国家科学院院刊》。以到2020年为限，如果分别让十一种方式为美国汽车10%的公里数供能的话，他们对颗粒水平及地面臭氧所产生的变化作出了预测——细颗粒物和地表臭氧是造成空气污染的两种主要成分，在美国每年有10万人死于空气污染。
　　
　　It was no surprise that electric cars whosebatteries were topped up from wind, solar or hydroelectric sources came outcleanest, causing 231 putative deaths over the course of a year, compared with878 for petrol cars. Electric cars recharged with power from natural-gas-firedstations were also a lot less lethal than petrol-driven ones, with 439 deaths.But if those same electric cars were recharged ultimately by coal, they wouldbe responsible, according to the model, for just over 3,000 deaths.
　　
　　电动汽车的电池由风能、太阳能、水力发电充电是最清洁的，这一点并不令人感到惊讶，假定这种情况造成的污染会导致每年有231人死亡，而燃油汽车的数字是878。如果电动汽车充电使用的是天然气发电站的话，造成污染致死人数为439人，这同样远远少于燃油汽车的。但如果那些电动汽车采用得是火电场供电的话，预测死亡人数将会超过3000.
　　
　　Biofuels also caused more health problems thanpetrol. But diesel, which is generating concern about pollution in parts ofEurope, where it is a more popular fuel than in America, was marginally cleanerthan petrol. This is because the Minnesota model assumes for all cars thatpresent and future emission-control technologies will be more widely used in2020, especially particulate filters which have a marked effect on cleaningdiesel exhausts. Diesel cars also have better fuel economy than petrol-drivenones.
　　
　　相比于使用燃油汽车，采用生物燃料充电的话会造成更多环境污染。但是在欧洲的某些地区，柴油引起了关于污染的担忧，因为柴油在欧洲要比在美国使用得更广泛，柴油在过去要稍稍好于汽油。这是因为克里斯托弗特塞姆、杰森希尔和朱利安马绍尔的研究假定对所有汽车来说，现在的或是未来的排放控制技术在2020年会被广泛的使用，尤其是颗粒过滤技术在降低柴油尾气污染方面有着显著的作用。柴油汽车也比汽油汽车拥有更好的燃料燃烧效率。
　　
　　Overall, the research shows that electric cars arecleaner than those that rely on internal-combustion engines only if the powerused to charge them is also clean. That is hardly a surprise, but the magnitudeof the difference is. How green electric cars really are, then, will dependmainly on where they are driven. In France, which obtains more than half itspower from nuclear stations, they look like a od bet. In China—which is keen on electric cars, but produces some 80%of its electricity from coal—rather less so.
　　
　　总之，研究显示只有在给电动汽车充电的能源也是清洁的情况下电动汽车要比那些依靠内燃机的汽车更加清洁。这点不足为奇，但各中差异之大令人瞠目结舌。电动汽车会有多么环保，每个国家的情况都不一样。在法国，一半的电能来自于核能，这看起来是一个不错的方法。中国正在大力推进电动汽车，但是80%的电动汽车的电能来自于火电厂发电，还不如不用电动汽车呢。

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