THE Beijing Meteorological Bureau said Thursday the air in two of Beijing’s districts — Tongzhou and Fangshan — has been rated “hazardous,” as North China was enveloped in fog for the fourth day.

    Beijing currently bases its air quality information on particles of 10 micrometers or larger, known as PM10, and does not take into account the smaller particulates that experts say are most harmful to human health, or PM2.5.

    But authorities came under huge pressure to change the system last year when they ranked the air as only slightly polluted, despite thick smog that forced the cancellation of hundreds of flights and triggered a surge in face mask sales.

    The Beijing Environmental Protection Monitoring Center said on its official microblog Thursday that the PM10 data soared after Wednesday’s evening rush hour.

    Beijing’s environmental protection bureau said earlier this month it would provide hourly updates of PM2.5 measure ahead of the Lunar New Year, or Spring Festival, which starts Monday.

    Public anger was exacerbated by the discrepancy between the official data and that issued online and on Twitter by the U.S. Embassy in Beijing, which conducts its own measures of PM2.5.

    Chinese media has said that if PM2.5 were used as China’s main standard, only 20 percent of Chinese cities would be rated as having satisfactory air quality, against the current 80 percent.(SD-Xinhua)