Children are having to breathe in so much air pollution in some major cities in the developing world that they are comparable with heavy smokers, scientists heard on Sunday.

Professor Devra Lee Davis from the Washington-based World Resources Institute said the environmental studies undertaken by her organisation were alarming.

The institute has listed the 10 cities in the world with the worst air pollution and finds nine out of 10 of them in China. The fifth-worst city is in India.

Rapid growth combined with outdated technology has produced environments that pose a major threat to the health of city dwellers, she told the American Association for the Advancement of Science annual expo in California - particularly children.

Two packets a day

"Just by breathing, most children who live today in rapidly expanding urban areas in the developing world inhale the equivalent of two packets of cigarettes each day," she said.

The worst city is Lanzhou, in Gansu Province in northwestern China. The region has a large petrochemical industry and oil refineries.

As a consequence of the emissions from these industries, "the city rarely experiences a clear day."

The institute's work, funded by the World Health Organisation (WHO), the US Environmental Protection Agency and other groups, looked at three measurements of air pollution - total suspended particulates (TSPs), sulphur dioxide and nitrogen dioxide.

Health limits

These are taken to be good indicators of pollution caused by the burning of fossil fuels. WHO guidelines say the maximum permissible amount of TSPs is 90 micrograms per cubic litre of air.

According to the report, Lanzhou has more than 700 micrograms. "The reason why these children are at risk is because the technologies that are in place now to fuel their economies are technologies that are 30 to 40 years old.

"Cars in Beijing meet 1970 US standards," she said, with many vehicles still running on leaded fuel.

But she said the Chinese government had recognised the problem and was moving to upgrade buses, cars and trucks to cleaner standards. "Improving energy efficiency will have a major effect," she said.

The 10 cities listed in the report, in descending order of TSP levels, are Lanzhou, Jilin, Taiyuan, Jiaozuo, Rajkot in India, Wanxian, Urumqi, Yichang, Hanzhong and Anyang.