BEIJING -- One Friday more than two years ago, an air-quality monitoring device atop the U.S. Embassy in Beijing recorded data so horrifying that someone in the embassy called the level of pollution "Crazy Bad" in an infamous Twitter post. That day the Air Quality Index, which uses standards set by the Environmental Protection Agency, had crept above 500, which was supposed to be the top of the scale.
So what phrase is appropriate to describe Saturday's jaw-dropping reading of 755 at 8 p.m., when all of Beijing looked like an airport smokers' lounge? Though an embassy spokesman said he did not immediately have comparative data, Beijing residents who follow the Twitter feed said the Saturday numbers appeared to be the highest recorded since the embassy began its monitoring system in 2008.
According to the EPA, levels between 301 and 500 are "Hazardous," meaning people should avoid all outdoor activity. The World Health Organization has standards that judge a score above 500 to be more than 20 times the level of particulate matter in the air deemed safe.
Official measurements of PM2.5, fine airborne particulates that pose the largest health risks, rose as high as 993 micrograms per cubic meter Sunday night, then began to fall. Long-term exposure to fine particulates raises the risk of cardiovascular and respiratory diseases as well as lung cancer, according to WHO.
Beijing ordered government vehicles off the roads as part of an emergency response, while warning the smog will persist until Wednesday.
Hospitals were inundated with patients complaining of heart and respiratory ailments and the website of the capital's environmental monitoring center crashed. Hyundai's venture in Beijing suspended production for a day to help ease the pollution, the official Xinhua News Agency reported.
In online conversations, Beijing residents tried to make sense of the latest readings.
"This is a historic record for Beijing," Zhao Jing, a prominent Internet commentator who uses the pen name Michael Anti, wrote on Twitter. "I've closed the doors and windows; the air purifiers are all running automatically at full power."
Other Beijing residents online described the air as "post-apocalyptic," "terrifying" and "beyond belief."
The deterioration in city's air quality has been exacerbated by growth in heavy industries in areas surrounding Beijing such as steel making, smelting, power generating and petrochemical sectors, said Ma Jun, a Beijing-based environmentalist and founder of the Institute of Public and Environmental Affairs.
Exposure to PM2.5 helped cause a combined 8,572 premature deaths in Beijing, Shanghai, Guangzhou and Xi'an in 2012, and led to economic losses of $1.08 billion, according to estimates given in a study by Greenpeace and Peking University's School of Public Health published Dec. 18.
Bloomberg news contributed to this report.