Shanghai started publishing air quality reports on television screens in around 32,000 subway trains, buses, ferries and office buildings yesterday.

The information, which accompanies the hourly weather report, uses colors to illustrate the five-tier scale - blue indicates excellent air quality, green is good, yellow for slightly polluted, orange moderately polluted and red for serious pollution.

"We will issue warnings through rolling subtitles on the screens when the air is seriously polluted or such a situation is forecast," said Wei Huajun, director of Shanghai Environmental Protection Bureau's pollution control department. "Suggestions to the elderly, children and people with respiratory diseases to avoid going outdoors and to take precautionary measures will be offered along with the warning."

Similar reports have also been launched on China Mobile's 12580 daily cellphone newspaper, the Shanghai Environmental Protection Bureau's weibo, or microblog, and the bureau's website.

Wei said the bureau was considering a bilingual service in the future, considering the large number of expat residents and tourists in the city.

"Instant information will also be available through the bureau's weibo and a short message platform between the bureau and the media to better inform residents about possible bad air quality," Wei said. "A collaboration with education authorities will also be in place soon to suggest schools suspend outdoor physical course in seriously polluted days."

On May 5, the local environmental watchdog began trials of splitting air quality reports and forecast into three periods - from 6pm to 6am, 6am to noon and noon to 6pm.

Previously a day's air quality was measured from noon to noon. However, such reports and forecasts couldn't accurately reflect changes in air quality or allow the public to be warned in time of a sudden deterioration.

The problem was highlighted during the recent four-day spell of pollution blamed on sandstorms in north China.

Shanghai suffered two seriously polluted days on May 2 and 3 but local residents were informed about the bad air quality at night, too late to take necessary precautions.

The air quality on May 2 and 3 was so bad that Shanghai was ranked the most polluted in the nation at that time.