THE Shanghai Environmental Protection Bureau issued a yellow air pollution alert at 11am today.

　　A yellow alert is triggered when the Air Quality Index is forecast to be between 201 and 300, or heavily polluted.

　　The AQI went above 200 at 8am, and stayed at 220 by 12pm, according to the Shanghai Environmental Monitoring Center.

　　The density of PM2.5 particles, the major pollutant, was around 170 micrograms per cubic meter at noon, about seven times the WHO recommended standard of 25 micrograms.

　　The bureau suggested that local citizens should reduce outdoor activities.

　　Power plants have been told to switch to green energy for power generation, while industries have been asked to reduce production and pollution.

　　Construction sites have been told to stop work to lessen dust and outdoor straw burning is prohibited.