The Shanghai environmental authority announced on Thursday that it has adjusted its air pollution standards to reduce the number of alerts, adding that they will still be frequent in winter.

Experts say the move was a reluctant tacit acknowledgment of the city's poor air quality.

The municipality's Environmental Protection Bureau will now lift air pollution alerts when the concentration of PM2.5 - particulate matter smaller than 2.5 microns in diameter that can penetrate deep into human lungs - falls below 115 micrograms per cubic meter.