London's air pollution history has lessons for Beijing(2)

"You have to control both, but emphasis has to be place on controlling air pollution all of the time rather than responding to air pollution episodes," said Dr Fuller.

Like Beijing and other big cities, said Dr Fuller, London's size means that by the time air reaches the center it has already passed over suburban areas where it picks up pollution.

In addition, a recent period of poor air quality in London had been caused by pollution which may had originated mainly in Poland, but was brought to the city on easterly winds.

This had lessons for China. "Solving a big mega-city's air pollution problems is not simple. It involves action at a local level to look at abating traffic, and it requires action in the region around us which is the source, if you like, of long range air pollution," said Dr Fuller.

Diesel engines are a real problem, and a source of increased pollution in recent years.

Dr Fuller explained, "We have seen a huge change in the cars in London. If you go back 10 or 12 years fewer than 20 percent of new cars would have been diesels and now we are approaching 50 percent. Diesel engines produce a lot more nitrogen oxide and PM10 and PM2.5 particles; many of the benefits that we are getting from newer and supposedly cleaner vehicles on the road is offset by the increase in diesel vehicles," he said.

Qureshi agreed, "It is something which one can certainly learn from London. Our experience has been that when the emphasis has been to reduce carbon, exempting diesel cars from those targets adversely adds to the local pollution problem."

Dr Fuller said there was debate about policy, "Many people say electric vehicles are the future but implementing electric vehicles is very difficult; you need charging, infrastructure, technology changes in terms of batteries and so forth to take them from their prototype and early production stages into the mainstream."