BEIJING (AP) The wall of gray haze around the National Stadium and across the city cut visibility down to a mile. On the eve of opening ceremonies, Beijing's polluted air took center stage Thursday as the most visibly pressing problem for Olympic organizers who had promised to clean up the Chinese capital.
Despite China's enormous attempts to improve the air quality in the run-up to the Summer Games, the stubbornly thick haze that covered the city illustrated how difficult and elusive a target clear skies can be. In the end, it will come down to the wild card of weather: rain and wind.
"I hoped that the measures could have more effect than they had in the last week," said Zhu Tong, an associate professor at Peking University's College of Environmental Science and Engineering who has been advising the government on pollution issues.
"Unfortunately, we had meteorological conditions that weren't good for clearing up the sky. So the stagnant air in Beijing has helped pollutants accumulate. I really hope in the next couple weeks, we'll have conditions that will help us clear up the sky."
The forecast for Friday, the official opening ceremony for the games, was overcast skies with a slight chance of showers in the afternoon, China's meteorological agency said. But relief may come by the weekend, with a prediction of moderate rain that could help wash out pollutants.
On Thursday, Beijing's air pollution index was recorded at 96, which came close to exceeding the national level for acceptable air. Levels between 51-100 are considered moderate pollution, and anything over 100 is harmful to sensitive groups, including children and the elderly.
The Associated Press has been compiling its own pollution data since mid-July, recording snapshot readings of Beijing's worst pollutant - tiny dust particles known as particulate matter 10.
The independent spot checks collected from the Olympic Green, the main sports thoroughfare, showed that, even though there are dramatic ups and downs, PM 10 concentrations were often much higher than what the World Health Organization considers healthy. On Friday, AP readings showed a PM 10 concentration of 373 micrograms per cubic meter - far above the WHO guidelines for healthy air of 50 micrograms per cubic meter.
The notoriously dirty air in this megacity of 17 million has been a leading concern since Beijing won the bid for the Olympics in 2001. China has poured 140 billion yuan - $20 billion - into "greening" the city, including doubling the number of subway lines, retrofitting factories with cleaner technology and building urban parks. But environmental efforts have often been outpaced by constant construction and increased traffic.
To help ensure clean air for the Olympics, Beijing officials imposed drastic measures in mid-July, including pulling half the city's 3.3 million vehicles off the roads, halting most construction and closing dozens of factories.
Environmental officials say the measures are having an impact, noting a 20 percent drop in major pollutants in July, compared with the same time last year. However, it's clear the sweeping measures have failed to guarantee the crystalline skies China hoped to showcase. Instead, the past three weeks have been marked by extremes - going from pea soup haze to swirling blue skies, often after strong winds or a downpour.
Athletes participating in the Aug. 8-24 games have raised concerns from the start about the impact of the city's pollution on their health and their performance, with many choosing to train outside of Beijing.
Those concerns were again highlighted when four members of the U.S. cycling team wore face masks as they walked off the airplane when they arrived this week. They later apologized.
International Olympic Committee president Jacques Rogge praised China on Thursday for doing everything "feasible and humanly possible" to combat air pollution, and said conditions will be safe for athletes to compete.
Rogge reiterated that outdoor endurance events, such as the marathon, could be postponed or rescheduled if smog levels are too high. The IOC will monitor the air quality on an hourly basis at 21 reporting stations and receive 72-hour weather forecasts. Heat and humidity could also be a factor during the games.
Despite the concerns by athletes, there is little evidence that they or other short-term visitors would suffer long-term health damage because of pollution levels in Beijing, said Hans Troedsson, the head of the World Health Organization in China.
Instead, the group facing the biggest risks from pollution are the city's residents, he said. Long-term exposure to air pollution means increased chances of developing asthma, respiratory disease and heart disease, he said.
"We have to remember that it's not short-term exposure that's of concern, it's the long-term," he said. "For us, it's important to see how these (environmental) efforts are sustained."
If China remains committed to continuing these measures in the long-run, the result could be "a public health legacy after the Olympics," he said.