"Knowing clearly the types and sources of pollutants can also help the government to come up with more efficient measures to control air pollution in general," she said.

The World Health Organization said in a 2005 report that it was possible to derive a quantitative relationship between pollution levels and specific health complaints.

But previously, China had no nationwide surveillance network for that, Xu said.

The rising government recognition of the challenge and openness about air quality monitoring now made the work possible, she said.

Last month, Beijing started to issue its PM 2.5 readings.

Compared with the PM 2.5 standards set by the World Health Organization and by the US environmental authorities, "the air pollution in our city is serious", Xu said.

No one group or sector of society reacts in the same way to air pollution for various reasons, including age and health, Xu said.

Pollutants can cause a range of health problems but primarily they are responsible for decreased lung capacity, shortness of breath, coughing and eye and nose irritation.

Monitoring and legislation can be of immense benefit in the fight to ensure air quality.

In the 1940s the US city of Los Angeles was hit by severe smog that led to hundreds of deaths from respiratory illness, Xu said. But legislation to ensure cleaner air was introduced and this led to a measurable improvement in air quality in the following decades.

Wang Qiuxia, a researcher with the Green Beagle, a non-governmental organization based in Beijing, said even with intervention it takes a long time to tackle air pollution.

Zhao Yue, a senior engineer at the Beijing Municipal Environmental Monitoring Center, urged the government to give more financial and technical support to monitoring PM 2.5.