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[BEIJING] Residents of the world's largest cities are ideally positioned to achieve the twin goals of clean air and lower carbon emissions, according to scientists in China and the US.

The sheer density of populations in the world's 19 megacities — cities containing 10 million people or more — means the financial resources are available to tackle the combined problem of air pollution and climate change, say environment scientist Zhu Tong from Peking University and David Parrish from the National Oceanic and Atmospheric Administration in the US in an article published in Science last month (30 October).

Making public transport and buildings more energy efficient is key to cleaning the air and lowering overall energy consumption, argue the article's authors.

"If proper measures are taken, we can not only reclaim clean air in megacities, but also reduce carbon dioxide emissions," Zhu told SciDev.Net.

He added: "More advanced technologies and a better chance of generating wealth and managing energy enable megacities to reduce air pollution and control climate change in a more efficient way."

Residents of megacities are exposed to airborne particles and ozone that are known to cause severe health problems, including respiratory and cardiovascular diseases.

All of today's megacities fall below the WHO standard for particulate matter, and the problem of pollution mushrooms as cities grow.

Half of humanity now lives in cities and the number of megacities is expected to reach 27 by 2025.

The two goals have often conflicted rather than coincided, the scientists observed.

Traditionally,  catalytic converters have been used to reduce vehicle exhaust fumes, but these do not lower carbon dioxide emissions, says Zhu. Driving clean-energy vehicles, on the other hand, tackles both problems.

Zhu cites Beijing as an example of a megacity that has successfully linked air pollution with climate change in its environmental policies.

During the 2008 Olympics, the city implemented harsh emissions controls on vehicles and also restricted heavy truck traffic at night, resulting in cleaner air.  

"Reducing air pollutants and controlling climate change generate co-benefits," agreed Wu Changhua, Greater China Director of The Climate Group.

The US and China are two countries that have incorporated carbon dioxide control as part of their strategy for reducing air pollution, said Wu.

Link to full paper in Science


Science 326, 674 (2009)