Smog thick enough to cancel flights hits Beijing

The outlines of buildings in the capital receded into a white mist as pedestrians donned face masks to guard against the thick, caustic air, which stranded passengers during the first week of the country's peak, six-week period for travel surrounding the Chinese New Year on Feb. 10.

The U.S. Embassy reported a peak level of PM2.5 — one of the worst pollutants — at 526 micrograms per cubic meter, or "beyond index," and more than 20 times higher than World Health Organization safety levels over a 24-hour period.