这是因为在这两个城市的白天时段，平均下来周日的二氧化氮浓度要低大约20%。

That is because, during daytime hours, the concentration of NO2 in those cities was, on average, about 20% lower on Sundays.

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根据这一年的数据记录，伦敦白天的二氧化氮浓度平均要超出世界卫生组织限值的41%。

In London, during daytime, the concentration of NO2 exceeded the WHO's limit by 41%, on average, over the 12 months examined.

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这些问题引起了全球关注。由于北京空气中的一氧化碳和二氧化氮浓度很高，会给运动员的呼吸系统带来伤害。

Such issues are drawing international concern, because Beijing's high levels of carbon monoxide and nitrogen dioxide could cause breathing problems for Olympic athletes.

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