If Beijing's "sauna weather" returns during the Olympics, officials will need to pull more cars from the roads to ensure good air quality, experts said on Wednesday.

Professor Zhu Tong, of Peking University, as an air quality adviser to the Beijing Olympics, said curbs on cars and factories were having the desired effect in improving the air quality for the Olympics.

However, high humidity and a lack of wind could trap emissions and particulate matter in the air, causing pollution levels to rise, said Zhu.

Officials would then have to consider further measures, including banning from the roads pre-Euro 3 emissions standard vehicles, he told the media in a group interview.

A more radical measure would be to allow only vehicles on which had the last number of the license plate matched the last number of the day of the month, effectively banning 90 percent of privately owned cars.

"But I cannot ensure whether the government will take these measures. Even if the measures are strengthened, the enforcement will last only three or four days," he said.

"Statistics showed that the nitride in the air has dropped by 48 percent since July 20 when a series of curbs were implemented to improve air quality ahead of the games," said Liu Zongchao, a researcher of World Economics and Politics Institute of Chinese Academy of Social Sciences.

The curbs included relocating Beijing Shougang Group, one of China's leading steel makers and the city's major polluter, taking half the city's 3.3 million vehicles off the roads, halting most construction, building more waste treatment facilities and relying more on geothermal resources.

Neighboring Tianjin and the nearby provinces of Hebei, Shanxi and Shandong, plus Inner Mongolia Autonomous Region, are helping the capital attain its anti-pollution goals. These efforts include closing major polluters, removing obsolete taxis from the roads and restoring grassland vegetation.

Beijing's air pollution index for particulate matter dropped to 44 on Wednesday from 90 on Tuesday.

A reading below 50 is considered good air quality and between 51 to 100 is moderate, according to the Beijing Municipal Environment Protection Bureau.

(Xinhua News Agency July 31, 2008)