Tourists take photos amid heavy fog in Shanghai, east China, Jan. 14, 2013. [Xinhua]

Shanghai will experience dense fog and haze over the next two to three days, city forecasters said yesterday.

Air quality should improve with the arrival of a cold front from the north, but that could be temporary, Man Liping, chief service officer of the Shanghai Meteorological Bureau, said.

"The wind can blow off the pollutants accumulated in the air, while the air quality may get bad afterward since the cold front also can bring sand and dirt," she said.

The city's air quality worsened again yesterday after Sunday's rain and wind from the sea ceased, causing the PM2.5 index to rebound from 20 micrograms per cubic meter at 3pm on Sunday to 150 micrograms at 10am yesterday. The readings at midnight were 97.9 micrograms per cubic meter.

The city's 24-hour average of PM2.5 was 127.6 micrograms per cubic meter at 12am, compared with the nation's safe limit of 75 micrograms.

PM2.5 particles, airborne particles smaller than 2.5 micrometers in diameter, are the main cause of urban smog and haze and harmful to health.

The lack of wind led to lingering fog in Chongming County and Fengxian District and light haze in other parts of the city yesterday.

More than 100 flights were canceled and another 100 delayed because of fog at the city's two airports.