Daily average concentration of various pollutants also has a close correlation with ground wind velocity.

各种污染物日平均浓度值与地面风速相关也非常好。

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The average concentration of ozone, one of the most common pollutants, is about half its level in the early 1990s, when the air was at its dirtiest (see chart).

20世纪90年代，空气污染时最严重时（如图所示），臭氧这种最常见的污染物的平均浓度大约是安全浓度的一半。

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The average concentration of particulates in city air during 2008, for example, was six times the ideal standard recommended by the World Health Organization.

以2008年全年的数据为例，北京市市区空气单位体积微小聚合颗粒数是世界卫生组织标准的6倍。

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For the first time, scientists measured an average concentration of atmospheric carbon dioxide of 400 parts per million in Mauna Loa, Hawaii, where the National Oceanic and Atmospheric Administration observatory is located, on Thursday.

CNN: CO2 levels hit new peak at key observatory

Before the 19th-century Industrial Revolution, the average carbon dioxide concentration worldwide was about 280 parts per million.

CNN: CO2 levels hit new peak at key observatory

The share of professional services jobs in the local economy is two and a half times the national average, the highest concentration in the country.

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