BEIJING — The International Olympic Committee's chief medical official expressed confidence today that air pollution will not pose a "major" risk to athletes and visitors at the Beijing Games.

Arne Ljungqvist, chairman of the IOC medical commission, said the committee is evaluating the city's air quality based on standards set by the World Health Organization.

"Those standards are fairly tough to meet, but in many respects the Beijing area does so," Ljungqvist said on the opening day of the IOC's three-day session. "I'm sure, I'm confident the air quality will not prove to pose major problems to the athletes and to the visitors in Beijing."

Beijing's polluted air has been one of the biggest worries for Olympic organizers and prompted drastic measures earlier this month that included pulling half the city's 3.3 million vehicles off the road, halting most construction and closing some factories in the capital and surrounding provinces.

The IOC will receive data every hour to monitor the situation throughout the Aug. 8-24 games.

"We will evaluate those and, should problems arise, we may have to take some action," Ljungqvist said.

The IOC has said outdoor endurance events, such as the marathon and road cycling race, could be postponed and rescheduled should smog levels be too high.

Today, Beijing was shrouded in a light gray haze.

Ljungqvist said he met with the WHO's local representative in Beijing three days ago who expressed concern over the "exaggeration of the problem that has been seen in the media."

Ljungqvist said the WHO standard was meant only as a guideline for protecting the long-term health of local residents, not for temporary visitors such as Olympic athletes and visitors.

"That is a totally different matter," he said. "To come to a city even though the air quality (might be) inferior, the long-term effects should no longer be feared by temporary visitors."

Ljungqvist said the WHO has three standards for measuring air quality, and Beijing comes under the interim target for developing cities and countries.

He said athletes in Beijing will face the same conditions of high heat and humidity that were prevalent in Atlanta in 1996 and Athens in 2004.

"The mist in the air that we see in those places, including here, is not a feature of pollution primarily but a feature of evaporation and humidity," Ljungqvist said. "We do have a communication problem here. Once the misconception has become sort of established in the minds of people, it's not that easy to get the right message through."