Shanghai residents enjoyed a record 92.1 percent of days last year when the air quality was excellent or good, the top two levels of a five-level scale, but more than 60 percent of polluted days fell in November and December, the worst for the past five years.

The figures have raised concerns about air quality after the World Expo.

Strict measures to control dust from construction sites and hay burning are under discussion in a bid to maintain the blue skies that the city enjoyed during the Expo period, officials from the Shanghai Environmental Protection Bureau said yesterday.

Shanghai had 29 polluted days last year, including two seriously polluted days on March 21 and November 13. Eighteen of the polluted days were recorded in November and December, six days more than in 2009.

Major pollutant

Excessive inhalable particulate matter is the major pollutant leading to local poor air quality.

The density of particulate matter in the past two months grew by 32 percent and the amount of nitrogen dioxide in the air grew by 12.3 percent over the same period of last year.

This is believed to be due, in part, to local construction sites and hay burning restarting after the World Expo ended on October 31 and less frequent road cleaning and washing after the event had closed its doors.

Dust brought by sandstorms in northern areas, pollutants coming in with the recent cold front and local pollution are the major causes tarnishing the air.

On eight polluted days when there was little wind, Shanghai also suffered a high level of nitrogen oxides, which are mainly from industrial production and vehicle exhausts.

Climate change

"Sandstorms polluted 13 days last year, much more serious than previous years," Wu Qizhou, the environment bureau's vice director, said. "A wide scale of climate change, like more frequent sandstorms and drier weather in winter, will make them a major polluter for Shanghai in the following years."

The bureau said that tougher environmental protection policies will be worked out for the next five years.

During the first quarter, the bureau is to issue warnings on television and radio programs when poor air quality is expected. The service will also be broadcast on buses and Metro trains and on messages to mobile phones.

Currently the service is available on the Shanghai Environmental Monitoring Center's website.

"The elderly, parents of children, those with respiratory diseases and special facilities like hospitals and schools can be alerted by the warnings," said Wu.