Yellow warnings trigger measures to cut emissions; wind on Saturday will help

Beijing and Tianjin issued yellow alerts for smog on Thursday afternoon, requiring polluting companies to suspend production to lower emissions. The smog is forecast to linger until around noon on Saturday, the national environmental monitoring authority said.

Shijiazhuang in Hebei province saw pollution rise to the most severe level, and many other cities - including Baoding in Hebei province, Beijing and Tianjin - reached their second-worst pollution mark by 4 pm, according to the China National Environmental Monitoring Center. The air quality index in Beijing, for example, hit 235.