Chai Fahe, deputy head of the China Research Academy of Environmental Sciences, said the areas not only suffer from worse air pollution than their neighbours, but also have longer lasting smog, the People's Daily reported.
The hot spots are located in the Beijing-Tianjin-Hebei cluster's northern and central areas, which have consistently been among the worst of China's 74 major domestic cities for smog since 2013.
Chai said the hot spots needed "extra strict" regulations to reduce pollutant emissions and help alleviate regional smog issues.
Since November, the Beijing-Tianjin-Hebei cluster has been hit by three bad spells of smog.
In December, the average concentration of PM2.5-particulate matter with a diametre less than 2.5 microns that is hazardous to health-climbed to 143 micrograms per cubic metre, the highest monthly reading since February 2014, according to the China National Environmental Monitoring Centre.
A pilot project to adopt unified standards for issuing alerts that was begun by the six core cities will end on March 15, the end of the municipal heating season.
However, more cities in the region are expected to follow suit in adopting unified standards next season.