The concentrated supply of heating, the relatively heavy humidity in the air and unfavorable conditions for air circulation have combined to worsen the smog that has suffocated a vast swathe of China's northern and northeastern regions over the past week.

Data released by the Beijing Environment Monitoring Center on Sunday morning indicate that the PM2.5 density in Beijing's urban area reached 245 micrograms per cubic meter, while the PM2.5 density in Shenyang, capital of Liaoning province, was a shocking 1,400 micrograms per cubic meter a few days ago.

Even though the serious air pollution Beijing, Tianjin and some cities in Hebei province are suffering from has become a regular occurrence on the arrival of winter and is now expected by residents, the continuous and widespread smog over such a large part of the country for so many days has fueled public grievances and provoked serious concerns about its effect on people's health.