|January 14, 2013
People refused to venture outdoors and buildings disappeared into Beijing’s murky skyline on Sunday as the capital’s air quality 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.
The Beijing center recommended that children and the elderly should stay indoors, and others should avoid outdoor activities.
The US Embassy also publishes data for PM2.5 on Twitter, and interprets the data according to more stringent standards.
In the 24-hour period up to 10 a.m. Sunday, it said 18 of the hourly readings were “beyond index.” The highest number was 755.
The U.S.’s Environmental Protection Agency’s air quality index only goes up to 500 and it advises anything greater than 300 would trigger a health warning of “emergency conditions” with the entire population likely affected.