Two smog hot spots in the already badly polluted Beijing-Tianjin-Hebei cluster have been identified by a national environmental think tank.

Chai Fahe, deputy head of the China Research Academy of Environmental Sciences, said the areas not only suffer from worse air pollution than their neighbors, but also have longer lasting smog.

The hot spots are located in the cluster's northern and central areas, covering some parts of Beijing as well as Baoding, Shijiazhuang, Hengshui, Langfang and Cangzhou in Hebei province, which have consistently been among the worst of China's 74 major domestic cities for smog since 2013.