It is frustrating now because we are stagnating at a terrible air quality level.

现在的情况很令人沮丧，因为我们停滞在一个很糟糕的空气质量中。

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Urban air quality level is token by air quality index (API), whose spatiotemporal change can reflect the change of urban air quality.

城市空气质量水平是以空气质量指数(API)来表征的，API的时空变化可以反映城市空气质量的变化过程。

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Analyze the main index, which include API, primary pollutant, air quality level, in 86 cities of china from Urban Ambient Air Quality Daily Report of 2006.

收集了2006年《重点城市空气质量日报》中中国86个重点城市空气质量主要分析指标——空气污染指数（A PI）、首要污染物、空气质量级别，并对数据进行统计分析。

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If you were outdoors in air quality of that level, you'd be told to go indoors and not do any physical activity.

BBC: Stub out car smoke, says charity