BEIJING — Pollution in Beijing was so bad Friday that the U.S. Embassy, which has been independently monitoring air quality, ran out of conventional adjectives to describe it, at one point saying it was "crazy bad."

The embassy, which issues hourly pollution reports via Twitter, later deleted the phrase from a  post, replacing it with "beyond index," and saying it was an "incorrect" description. The embassy said it would also revise the language to use when the air quality index goes above 500, its highest point and a level considered hazardous for all people by U.S. standards.

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The hazardous haze has forced schools to stop outdoor exercises, and health experts asked residents, especially those with respiratory problems, the elderly and children, to stay indoors.

"We've canceled 10 days worth of games since August," said David Niven, chief operating officer of China ClubFootball, which runs extensive youth and adult football leagues in Beijing.

"If the air is above 240, some of the schools will ask us to move football games indoors or cancel them altogether," he added. "Because of the bad air this year, we've had to cancel more games than ever before."

Health experts say breathing polluted air can affect respiratory functions and worsen problems for those with asthma or allergies.

China's official air quality rating was 312 on Friday.

Environmental groups and city residents have complained the government's measurement system consistently underreports the severity of the problem.

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Beijing's official air monitors only measure relatively coarse particulate matter, whereas the U.S. system monitors smaller, deadlier dust particles.

Experts say Beijing's frequently bad air has been even dirtier recently because a growing number of factories and villages on the outskirts of the city are burning coal for the winter, and more than 1,200 new cars hit the roads each day.

The capital underwent a massive cleanup in 2008 for the Olympic Games and also planted thousands of acres of trees in and around the city to attempt to reduce the problem, but has since allowed some factories to reopen and lifted some traffic restrictions, bringing pollution levels back up.

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"If the city's planning was better, people from the outskirts wouldn't have to commute for hours each day," said Ma Jun, director of the Institute of Public and Environmental Affairs in Beijing.

"Beijing needs to place more of a priority on the environment. The health of Beijing residents is no less important than the health of those athletes who were here for a few weeks," Ma added. "We can't just expect wind, snow or rain to wipe out the pollution when it gets bad. The city must take pollution more seriously and implement preventive measures."

One Beijing resident said he was suffering breathing difficulties.

"I feel like I'm having some problems with breathing and distress in my chest," said a high school teacher who only gave his surname, Qiao.

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