世衛組織：伊朗、南亞城市空氣質量最糟

Cities in Iran, India, Pakistan and the capital of Mongolia rank among the worst on the planet for air pollution, while those in the US and Canada are among the best, according to the first global survey, released Monday by the World Health Organization.

The southwest Iranian city of Ahvaz walked away with the unfortunate distinction of having the highest measured level of airborne particles smaller than 10 micrometers.

WHO released the list to highlight the need to reduce outdoor air pollution, which is estimated to cause 1.34 million premature deaths each year. The global body said investments to lower pollution levels quickly pay off due to lower disease rates and, therefore, lower healthcare costs.

The list, which relies on country-reported data over the past several years, measures the levels of airborne particles smaller than 10 micrometers — so-called PM10s — for almost 1,100 cities.

WHO recommends an upper limit of 20 micrograms for PM10s, which can cause serious respiratory problems in humans. They are mostly sulfur dioxide and nitrogen dioxide from power plants, auto exhausts and industry.

Ahvaz's annual average of PM10s was 372 micrograms per cubic meter.

The study found that the Mongolian capital Ulan Bator had an annual average PM10s density of 279 micrograms per cubic meter, followed by another west Iranian city, Sanandaj, with 254 micrograms.

Cities in Pakistan and India, such as Quetta and Kanpur, as well as Botswana's capital Gaborone, also ranked high on the pollution scale.

WHO said the reasons for the high pollution levels varied, but that often rapid industrialization and the use of poor quality fuels for transportation and electricity generation are to blame.

At the other end of the list are cities in Canada and the United States, which benefit from lower population density, favorable climates and stricter air pollution regulation.

Yukon territory's capital Whitehorse had a yearly average of just 3 micrograms of PM10s per cubic meter, while Santa Fe, New Mexico, measured 6 micrograms.

Washington, D.C., had a level of 18 micrograms, Tokyo measured 23 micrograms, and Paris had 38 micrograms of PM10s per cubic meter.世界衛生組織週一發佈的首次全球調查顯示，伊朗、印度、巴基斯坦的城市和蒙古首都是全球空氣污染最嚴重的，而美國和加拿大城市的空氣質量是最好的。

伊朗西南部城市阿瓦士不幸成爲空氣最糟城市，該市空氣中小於10微米的顆粒物含量是最高的。

世界衛生組織發佈這一排名是爲了強調減少室外空氣污染的必要性，據估計室外空氣污染每年造成134萬人過早死亡。該全球機構說，降低污染水平的投資很快能得到回報，因爲污染減少能夠降低疾病發生率，從而減少醫療開支。

該排名是依據各國在過去幾年內報告的數據得出的，測量了近1100個城市空氣中小於10微米的顆粒物（可吸入顆粒物）的含量。

世界衛生組織建議可吸入顆粒物的上限爲20微克，這種體積的顆粒物將導致嚴重的人體呼吸系統疾病。這些顆粒物大多爲發電廠、汽車工業和汽車尾氣排出的二氧化硫和二氧化氮。

阿瓦士年均可吸入顆粒物含量爲每立方米372微克。

研究發現，蒙古首都烏蘭巴托年均可吸入顆粒物濃度爲每立方米279微克，其後是又一個伊朗西部城市，薩南達傑，濃度爲每立方米254微克。

巴基斯坦和印度的城市，如奎達市和坎普爾市，還有博茨瓦那首都哈博羅內，污染水平也排在前列。

世界衛生組織說，導致高污染水平的原因各有不同，不過通常是由迅速工業化及在交通和發電上使用低質量的燃料導致的。

在污染排行中最靠後的是加拿大和美國的城市，受益於較低的人口密度、優越的氣候和較嚴格的空氣污染法規。

加拿大育空特區的首府懷特霍斯年均可吸入顆粒物含量僅爲每立方米3微克，而美國新墨西哥州首府聖非也只有6微克/立方米。

華盛頓哥倫比亞特區的年均可吸入顆粒物含量爲18微克/立方米，東京爲23微克，巴黎爲38微克。