People refused to venture outdoors and buildings disappeared into Beijing's murky skyline on Sunday as the air quality in China's notoriously polluted capital went off the index. The Beijing Municipal Environmental Monitoring Center said on its website that the density of PM2.5 particulates had surpassed 700 micrograms per cubic meter in many parts of the city. The World Health Organization considers a safe daily level to be 25 micrograms per cubic meter. PM2.5 are tiny particulate matter less than 2.5 micrometers in size, or about 1/30th the average width of a human hair. They can penetrate deep into the lungs, so measuring them is considered a more accurate reflection of air quality than other methods.
keyboard shortcuts: V vote up article J next comment K previous comment