![A man cleans his car covered by dusts in Beijing at 11 p.m. on March 30, 2012. [Beijing News/ Han Meng and Wang Jianing]](U371P886T1D11710F12DT20120331134826.jpg "A man cleans his car covered by dusts in Beijing at 11 p.m. on March 30, 2012. [Beijing News/ Han Meng and Wang Jianing]")
A man cleans his car covered by dusts in Beijing at 11 p.m. on March 30, 2012. [Beijing News/ Han Meng and Wang Jianing]
The density of particulate matter smaller than 10 Microns (PM 10) increased sharply in a few hours in Beijing on Friday as an unexpected floating dust hit the city, according to the statistics of Environment Monitoring Center.
The PM 10 index reached 1,000 micrograms per cubic meter in Haidian, making it the worst polluted district in Beijing yesterday.
When the PM 10 index of a certain region exceeds 500 micrograms per cubic meter in 24 hours, this area is considered to be heavily polluted according to the stipulation of the monitoring center.
The sharp increase of PM 10 index was due to the floating dust which was blown to Beijing by the northwest wind from other places. Neither the meteorological offices nor the environmental authorities have warned of a sandstorm.
The city's meteorological office later explained that the difference between sandstorm and blowing-sand is the visibility. What hit Beijing was just a blowing-sand and the meteorological office had made forecast for it before it happened.
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