The Beijing Municipal Environmental Monitoring Center said on its website that the density of PM2.5, or airborne particulates measuring less than 2.5 micrometers in diameter, had surpassed 700 micrograms per cubic meter in many parts of the city, some areas even reaches 1000 and "beyond index", which means the air pollution has surpassed the upper limit their newly erected instruments can measure.
"These figures represent extremely bad pollution. Pollutants have gradually accumulated over the course of recent windless days, making the air quality even worse," said Zhu Tong, a professor from the college of environmental sciences and engineering at Peking University.
Beijing began to measure PM2.5 only late last year, before only PM10 was measured. PM2.5 is more reliable for evaluating the air quality according to World Health Organization, which considers a safe daily level to be 25 micrograms per cubic meter.
On the same day PM2.5 index in Washington stands at 54.
The municipal meteorological station issued the city's first orange fog warning Sunday morning due to decreased visibility caused by the heavy smog.
And residents of Beijing are recommended to stay indoors. While some people followed the warning, Beijing’s streets were still fairly busy Sunday, and there was the familiar sight of heavy traffic on main thoroughfares.
The heavy smog shrouding Beijing is expected to last until Wednesday, when wind will arrive to blow the smog away, according to a weather report from the meteorological station.
The air quality in other parts of China is not better.
China's meteorological authority issued a yellow alert for the heavy smog that continues to shroud the country's northern, central and eastern regions on Sunday. The air quality of 33 large cities of China is classified as heavy polluted and health risky.
Beijing, Tianjin, Shijiazhuang, Baoding, Handan, Jinan, Zhengzhou, Wuhan are some of the cities with heaviest air pollution. PM2.5 readings in these city all surpass 500 on Sunday.