"There is a nexus between local air pollution and global climate change," Mylvakanam Iyngararasan, senior programme specialist for the United Nations Environment Programme, told the annual "Better Air Quality" conference at a meeting in the home of the Taj Mahal.

"Research suggests that there will be a large drying-out effect from the air pollution we see now. Harmful chemicals, aerosols and other pollutants impact cloud formation. India has experienced severe droughts in the last few years.

"Pollution from China can be blown in days to India or in a matter of weeks travel to Europe so pollution really is a trans-border problem," he added.

Jitendra Shah, senior environment engineer with the World Bank in Washington, said Asian countries needed "to do their bit to keep the neighbourhood clean."

"No country can build a giant air filter on its borders so all countries have a responsibility to clean their own house in order to keep the neighbourhood clean," said Shah.

Experts also noted there were ample studies which showed there was a blanket of chemicals and dust from cars, aerosols and industrial smokestacks in South Asia.

In 1998, Indian-born US scientist Veerabhadran Ramanathan used planes, ships, satellites and a team of 250 scientists from 15 countries to track a cloud of pollution dubbed the "Asian Brown Cloud" that hung over the Indian Ocean.

The cloud has injected intense rancour between the United States and developing countries over the cause of global warming.

The discovery provoked denials from Indian officials who felt the country was being singled out as a culprit in global warming and was seen as vindicating the Bush administration when it pulled out of the global Kyoto climate treaty.

Ramanathan has maintained that Los Angeles, New Delhi, Bombay, Beijing and Cairo contribute the most to a worldwide circle of pollution.

"Pollution is by no means restricted to the Asian region," countered Indian scientist A.K Singhal. "There is a haze over Los Angeles and a thick plume of pollution over most big North American cities," he added.

"There is no way we can contain air between city boundaries so we have to be concerned about the long-range transport of air pollutants in Asia which have serious climate change implications," said Elisea Gozum, former secretary of the Philippines environment department.

About 500 delegates are attending the Agra meeting hosted by India's environment ministry, the Clean Air Initiative for Asian Cities -- a grouping of government agencies, NGOs and others -- and the Society of Indian Automobile Manufacturers.

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