Class 2 control regions means areas that meet air quality standards, with the exception of Class 1 control regions.

二级防制区，指一级防制区外，符合空气品质标准区域。

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In 2004, 210 cities exceeded the Class 2 limit values of the National Ambient Air Quality Standard (NAAQS) within the total 342 monitored cities.

2004年，受监测的342个城市中有210个城市的空气质量超过了国家环境空气质量标准的二级标准。

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Air here is fresh with first-class air quality throughout the year. It is called "the Natural Oxygen Bar" consequently.

这里空气清新，一年四季空气质量都在一级，素有“天然氧吧”之称。

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Yes, China faces a world-class air quality problem.

FORBES: Magazine Article

In China, basic things such as uncontaminated baby formula, clean air, top-quality schools and private hospitals are luxuries, out of reach of many members of the middle class.

WSJ: An Unhappy Middle in the Middle Kingdom