With a single day to go before the Olympics, both government and independent readings suggest that Beijing's air is getting worse.
And if the winds don't change, this could wind up being one of the most polluted Olympics in modern history, with more particulate matter in the air than Atlanta in 1996 or possibly even notoriously smoggy Los Angeles in 1984.
Despite the government's anti-smog efforts, the entire Beijing region's pollution has been locked in by a stubborn summer weather pattern that brings air pollution up from the south, said Kenneth Rahn, a Rhode Island professor who has been studying Chinese air quality for almost a decade.
Olympic organizers could get lucky, though, if the weather pattern breaks before the actual competitions begin later this week. But the bad weather is likely to return some time during the games, demonstrating how difficult it is to control the air quality of a city.
"This cyclic pattern will continue because it always has. That's the nature of Beijing," Rahn said.
Like many other cities, Beijing's pollution problems result from a combination of massive amounts of human activities and less-than-ideal geography. And the city's mix -- despite traffic bans, factory shutdowns and construction halts -- could turn out to be the worst of any Olympic games.
Direct comparisons between host sites are difficult because air quality measurements vary. China uses the "air pollution index" which combines measurements of particulate matter, nitrogen dioxide, and sulfur dioxide. On that scale, a day with 350 micrograms of particulates per cubic meter of air -- seven times the World Health Organization's recommended levels -- could still receive an air quality rating of "slightly polluted."
Among recent Olympics, Beijing looks to be the most polluted city. For comparison, take Atlanta, as measured by Georgia's air-monitoring authorities. During the 1996 Olympics, the daily concentration of PM10, the dominant pollutant in Beijing, was 31 micrograms per cubic meter of air. Beijing, even with the most optimistic spin on the data, is averaging 111 micrograms per cubic meter of air since July 20th, or more than three times Atlanta's level of pollution, according to the Chinese government. Independent sensors deployed by the BBC and AP have detected local levels reaching into the 300s.
The Seoul Olympics of 1988 most closely mirror the Beijing Olympics, although, again, directly comparable data does not exist. Annual Korean data (.pdf) suggests PM10 levels of close to 150 micrograms per cubic meter of air, although air quality information was not accessible for the period of the Olympics.
Perhaps the most telling comparison would be between Beijing in 2008 and the notoriously smoggy Los Angeles in 1984. Unfortunately, data on PM10 is not available for Los Angeles for that time period. One analysis found that Los Angeles probably had PM10 levels of somewhere around 70.
If the weather patterns shift, the Chinese Olympic organizers could escape notice as having held the most polluted Olympics in memory. But their fate is, literally, in the wind. If they continue pushing southern pollution into the city, the opening ceremony will be smoggy, Rahn said. If they change direction, the opening ceremony air could be relatively clear.
"It seems to me that the authorities are not in a very nice spot right now," Rahn said. "They are having, at last, to come to terms with the fact that all their best laid plans might not work out. They might work, but they might not."