The spell of thick smog that blanketed Tian'anmen Square for 18 days in June will not be a thing of the past, according to weather experts.

Yan Peng, an atmospheric chemistry researcher of the Meteorological Observation Center of the China Meteorological Administration, and other researchers said the smog this summer may become a common occurrence if the high humidity remains steady.

"High humidity may cause low visibility, worsening smog," Yan said.