Fan Yuansheng, of the Ministry of Environmental Protection (MEP), said the two pollutants had caused great concern and the MEP was making technical preparations to monitor them.

"We should be able to start regular monitoring of ozone and PM2.5 (particle matter) next year, which would lead to measures to deal with them," Fan told a press conference.

He was speaking in response to reports that China's environmental authorities had failed to include fine particles and ozone into their pollution measurements, causing ignorance of health damage caused by the pollutants.

Fine particles, known as PM2.5, are tiny solid particles of 2.5 micrometers in diameter and smaller. Health experts believe they are unhealthy to breathe and have been associated with fatal illnesses and other serious health problems.

Colorless ozone is also believed to cause respiratory problems and to affect lung functions.

There have been worries that the air in Beijing, the Chinese capital that will host the summer Olympic Games in five days, may be unhealthy for some athletes competing outdoors to breathe.

China has taken drastic anti-pollution steps, such as closing factories surrounding Beijing and ordering half of 3.3 million cars in Beijing off the roads, to try to clean the sky during the Olympics.

"These measures have been effective so far," said Fan, Director General of the MEP's Department of Pollution Control.

Beijing basked under blue sky this weekend after being blanketed in a humid haze for a week. The Beijing Meteorological Bureau said on Sunday favorable weather conditions and a series of anti-pollution measures had combined to clear the normal smog above the city.

Fan Yuansheng refuted allegations that China's air pollution standards were more lenient than World Health Organization (WHO) guidelines.

Standards that China was using to control four major air pollutants - sulphur dioxide, nitrogen dioxide, carbon monoxide and particles - followed the WHO's "phase one" guideline issued in 2005, he said.

The WHO allows developing countries like China to begin from this guideline to eventually reach its stricter final goals, he said.

Fan said measures adopted to reduce pollution in Beijing for its hosting of the summer Olympics would stay in force after the event.

"Most of these measures are long-term ones and will remain after the Games. Not all the temporary measures will be retained after the Games, but they may provide clues for our future work," he said.

The Chinese government recently warned that more factories could be temporarily shut down and more cars could be restricted from the roads in Beijing if "extremely unfavorable weather condition" occur to deteriorate the air during the Games.

But many Beijing residents are more worried that air pollution could turn bad after the Olympics, with factories reopened, construction resumed and car no longer restricted.

Fan argued that the Olympics would leave environmental legacies to Beijing and China, which has spent billions to clean the environment polluted by rapid industrialization.

For example, the State Council, China's cabinet, has ordered all government cars to keep off the road for one day each week according the last figure of their plate number. This is a continuation of the temporary measures during the Olympic Games, Fan said.

The MEP has launched a research on how to further improve air quality in the entire northern China where Beijing is, since air pollution is not a problem of Beijing alone, he said.

Nearly 90 percent of coal-burning power plants in provinces neighboring Beijing have taken measures to reduce the emission of sulphur dioxide, and many vehicles have been upgraded to meet stricter emission requirements.

Lu Xinyuan, Director General of the MEP's Bureau of Environmental Supervision, said about 200 environmental inspectors have been sent to Beijing and five neighboring provinces to check enterprises on their anti-pollution work.

Meanwhile, 16 environmental groups based in Beijing on Sunday called on local motorists not to drive on Aug. 8, in order to help reduce pollution and road congestions when the Olympics open.

They further encouraged private car owners to use public transport as much as possible during the Olympics and the following Paralympics to "contribute a blue sky to Beijing."

The groups with over 200,000 members hoped the usage of private cars would be reduced by one million times if the campaign are well responded in the next two months, according to Yu Xinbin, member of the Global Village of Beijing, a non-governmental organization.