背景阅读：

　　经中国环境监测总站会同京津冀及周边省级环境监测中心预报，受不利气象条件影响，京津冀及周边地区将发生一次大范围重污染天气，此次重污染过程从16日下午开始，将一直持续至21日，持续时间长达6日，其间超过20个城市空气质量可能连续4天达到重度及以上污染，且可能出现2天以上的严重污染。本次重污染过程影响范围广、持续时间长、污染程度重。号称今冬最重雾霾!

　　While Beijing smothered Monday under a cloud of smog and a reputation for horrible air, other cities in the world quietly vie for the tarnished crown of world's most polluted city.

　　tarnished

　　v.(通常指金属) (使)失去光泽，(使)变灰暗( tarnish的过去式和过去分词 ); 玷污，败坏;

　　例句：

　　His image was tarnished by the savings and loan scandal.

　　他的形象因为那桩储蓄信贷丑闻而受损。

　　其他：

　　原型： tarnish

　　And this year's winner is: Zabol, Iran.

　　Beijing and much of northeastern China are currently shrouded in a smog red alert, causing some factories to shut down, highways to close and airlines to cancel flights. But the World Health Organization ranks the world's cities based on air pollution, and the worst Chinese city, Xingtai, only ranks ninth in the 2016 list.

　　WHO's ranking, released in May, is based on the amount of PM 2.5 – particle matter smaller than 2.5 microns in diameter common to dust, soot and smoke. PM 2.5 is nasty because it can get stuck in the lungs and cause or aggravate asthma and other long-term health problems.

　　diameter

　　n.直径，直径长; 放大率;

　　例句：

　　This hole was a scant. 23 inches in diameter.

　　这个洞眼的直径只有0.23英寸。

　　其他：

　　复数：diameters

　　WHO guidelines call for no more than 10 micrograms of PM 2.5 per cubic meter of air. Dusty Zabol averages a whopping 217. Other cities cracking the dubious list's top five include Gwalior, India, at 176, Allahabad, India at 170, Riyadh, Saudi Arabia at 156 and Al Jubail, Saudi Arabia at 152.

　　China chokes on smog so bad that planes can't land

　　Beijing suffered Monday with levels hovering above 200; other Chinese cities have pushed close to 1,000 in recent days.

　　The tide can be turned with effort. The 2015 most-polluted city, New Delhi, slid to 11 in 2016 thanks a crackdown that included bans on the most polluting cars and trucks and fines for for burning trash.

　　crackdown

　　n.压迫，镇压; 打击，制裁; 强制取缔;

　　例句：

　　The EU also staged a crackdown on harmful tax practices, including unequal treatment of residents and non-residents.

　　欧盟还对有害税收行为进行了打击，其中包括对居民和非居民的不公平对待。

　　其他：

　　复数：crackdowns

　　Breathe easier, America. The worst U.S. city didn't crack WHO's top 1,000. Visalia, Calif., checked in at 1,080.