这结果至少超过了美国国家空气质量标准的4倍。
That's at least four times greater than exposure standards set by U.
这结果至少超过了美国国家空气质量标准的4倍。
That's at least four times greater than exposure standards set by U.S. national air quality standards.
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。
In 2004, 210 cities exceeded the Class 2 limit values of the National Ambient Air Quality Standard (NAAQS) within the total 342 monitored cities.
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