Buildings are obscured by a thick haze in Xi'an, capital of Shaanxi Province, on Oct. 10. The dense haze continued in Beijing and neighboring areas for a third day on Friday. PM2.5 concentration levels reached more than 500 micrograms per cubic meter in parts of Hebei Province on Oct. 10. In the capital city of Beijing, PM2.5 levels have stayed above 300 micrograms per cubic meter since Wednesday and authorities has issued an orange alert for the hazardous smog. [Photo/CNS]