Forecasters clear up toxic fog panic (4)

"The best way to prevent being affected by the polluted fog is to stay inside. Masks are useless to protect the health," Zhang noted.

Zhou Rong, a climate and energy campaigner for Greenpeace, agreed with Zhang, saying that fog is not harmful if it is not combined with pollution.

Yet Zhou noted that the fog will contain many more pollutants in winter when the general heating system requires coal burning.

"Meanwhile, other polluted air produced by the heating systems in Tianjin and Hebei [Province] can affect Beijing, contributing more pollution to the city," she said.

"Given the presumption that fog is more likely to form PM 2.5 particles, then it would be easier to gather heavy metals in the air and then this contains more toxicity than regular fog," she noted.

The visibility was below 500 meters as the result of the fog that lasted for around 10 hours on Friday, People's Daily online reported Friday.