Even as Muscovites choked under a blanket of thick smoke in the first week of August 2010, concentrations of a colorless, odorless gas spiked to dangerous levels.

2010年8月的第一周，当莫斯科市民在一片厚厚的烟尘之下咳嗽不止时，一种无色无味的气体的大气浓度已经到达了危险的水平。

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Sydney's summer sun has disappeared under a blanket of smoke so thick at times that iconic structures such as the Sydney Opera House and the harbour bridge could not be seen from the city centre, and flights have had to be diverted to other places.

ECONOMIST: Arson suspected