BEIJING — The Beijing government put in place emergency measures Wednesday to try to combat thick smog that has encased the city in brown and gray soot. The measures include temporarily shutting more than 100 factories and ordering a third of government vehicle off the streets, official news reports said.

The effort came on the second straight day of air that is rated ‘‘hazardous’’ by the standards of the US Environmental Protection Agency. That rating, in which the air quality index surpasses 300, means people should not venture outdoors.