Shanghai will shut schools and order cars off the road in cases of severe smog as the city yesterday rolled out emergency measures to tackle air pollution.

They include a new air pollution alarm system, with blue, yellow, orange and red alarms indicating different levels of air quality.

China's commercial hub Shanghai is blanketed by dense smog on Dec. 2, 2013. [Photo/CNS]

When the red alarm is raised, apart from closure of primary and middle schools and kindergartens, 50 percent of official vehicles will be taken off the roads, large-scale outdoor activities will be canceled, and construction will be halted.

Shanghai previously had a two-level warning system for air pollution, issued last March. A warning of "heavy pollution" was issued when the air quality index reached 200 for 12 hours, and a warning for "severe pollution" when it reached 300 for six hours.

However, in practice the system proved unsatisfactory. In November, it took 27 hours to issue a heavy pollution warning, which led to a delay in schools being notified.

The Shanghai Environmental Protection Bureau said there were 241 days of good or excellent air quality last year, with the index below 100. Two days were severely polluted with the AQI over 300; 21 days heavily polluted (201-300); 29 moderately polluted (151-200), and 72 slightly polluted (101-150).

PM2.5, referring to tiny particles hazardous to health, was the main pollutant for 70 percent of the 124 polluted days. According to a target set by the Ministry of Environmental Protection, Shanghai is to reduce PM2.5 by 20 percent within five years.

The air quality index even surpassed 500, the top reading in the chart, in early December last year.

The air quality in January, November and December last year was reported to be the worst for the past five years.

In the new warning regime, a red alarm is triggered when the AQI is forecast to be over 450 for the next 24 hours, and will be made public via TV and text messages, and on official sites of government departments and public service platforms.

When a red alarm is issued before 6am on any day, schools and kindergartens will automatically suspend classes, no matter how much the air improves throughout the day.