BEIJING - Four days after the massive fireworks displays that marked Lunar New Year's Eve, Beijing's municipal weather bureau has maintained a warning against exercising outdoors due to the city's air pollution.

Readings for PM2.5, or hazardous particles measuring 2.5 microns in diameter or less, hovered between 200 to 250 micrograms per cubic meter Wednesday morning and are still increasing, the Beijing Environmental Protection Monitoring Center said Wednesday.

The municipal observatory said a lack of wind has allowed the smog to linger, as well as reiterated its call to lessen the use of fireworks.

The local government has sent text messages to mobile phone users asking them to use fewer fireworks in order to tame the city's heavy air pollution.

Sales of fireworks in Beijing dropped 37 percent year on year, with260,000 cartons sold from January to the first day of the Lunar New Year.

Beijing, which only permits fireworks to be set off during the Spring Festival holiday, has also shortened the amount of time that fireworks are allowed to be set off this year.

An official circular stated that fireworks will be allowed from February 9 to 24.