Citizens do morning exercise in Shanghai, China, Jan. 14. [File photo]

The dense haze that has shrouded Shanghai for the past few days is set to continue today as smog lingers in large parts of east and central China.

But the sky should clear tomorrow with the arrival of a cold front from the north and the air quality will be between "good" and "lightly polluted," the Shanghai Environmental Monitoring Center said yesterday.

The center issued an air pollution alert at 7:39am yesterday when the city's hourly PM2.5 index reached 96.1 micrograms per cubic meter. It urged people with cardiovascular and respiratory diseases to avoid outdoor activities.

The downtown density of PM2.5 pollutants, particles smaller than 2.5 micrometers in diameter, began to climb at 6am and reached 118 at 10am.

The average reading over the previous 24 hours was 116.2 at 10am, compared with the nation's safe standard of 75.

After 10am, the density began to drop and was 77.5 at 5pm.

While Shanghai was still experiencing poor quality air, Beijing was able to breathe more easily yesterday.