Choked 呛人

The most polluted cities of the world's largest economies
世界最大经济体中污染最严重的城市
BEIJING is frequently shrouded in dense, yellowish smog so thick that the other side of the road is obscured. But the deadly smog that enveloped the city over the past weekend was so bad that air-quality readings from a monitor on the roof of the American Embassy said simply: "Beyond Index". The embassy uses the US Environmental Protection Agency's air-quality index (AQI), which measures PM 2.5 (particulate matter of 2.5 microns across or less per cubic metre). Such particles are small enough to be inhaled and can damage lungs. The AQI range ends at 500; at one point a reading of 886 was recorded. A reading above 100 is deemed “unhealthy for sensitive groups” and anything above 400 is rated “hazardous” for all. These independent readings have put pressure on the authorities to release more detailed data of their own. A year ago Beijing's municipal officialsbowed to public pressure and started reporting data on PM 2.5 for the first time. But Beijing is not even the most polluted city in China. Using a different but more widely used measure collated by the World Health Organisation of larger particulate matter called PM 10 (particles of 10 microns or less), which allows cross-country comparisons, that dubious honour is bestowed on Lanzhou in the north-western province of Gansu (and the city of Ludhiana in India is more polluted still). Better data may soon be available. This month China’s Ministry of Environmental Protection announced that 74 cities were to begin monitoring and reporting the levels of multiple pollutants, including PM 2.5, sulphur dioxide, carbon monoxide and ozone. 

北京常常笼罩在黄色大雾之中，以至于连马路对面都看不清楚。不过在过去一周弥漫北京城的致命烟雾糟到极点，以至于美国大使馆屋顶的空气质量监测仪的读数为“超出指数”。美国大使馆使用美国环境保护局的空气质量指数测量PM2.5值（每立方米中直径小于等于2.5微米颗粒数目）。这些颗粒足够小，可以被人吸入，并对伤害肺部。空气质量指数的量程为500，一度还有866的记录可查。读数超过100被视为“会对敏感人群造成不适”，超过400被视为“对所有人群危险”。这些独立数据给当局以压力，迫使他们发布自己更为详细的数据。一年前，北京市政府迫于公众压力首次开始报告PM2.5数据。然而北京甚至不是中国污染最严重的城市。使用一种不同的但是更广泛使用的由世界卫生组织整理的方法，用更大的被称作PM10（直径小于等于10微米）的颗粒，对各国进行比较，“中国污染最严重的城市”这一“荣誉”落在西北甘肃省的兰州头上（印度的卢迪亚纳污染还要严重）。马上就有更好的数据。本月，中环境保护部长宣布74个城市即将监测并报告多种污染物的水平，包括PM2.5，二氧化硫、一氧化碳和臭氧。