Monitoring data showed the Air Quality Index in most parts of the capital reached 500, the maximum pollution level, on Sunday, the third consecutive day of severe smog.

监测数字显示，周日，首都北京大部分地区的空气质量指数均达到500，即污染程度的最高上限，北京的雾霾天气已持续三天。

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When determining air demand for tunnel ventilation, the air demand is taken from the bigger one between calculation of CO concentration index and smog concentration index.

隧道通风需风量的确定是取CO浓度指标和烟雾指标计算出来的较大者作为需风量。

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At the end of May the smog index rose high enough to trigger extra restrictions on cars.

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The heavy smog and haze that enveloped Beijing this weekend pushed the pollution index to a record high.

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