Its report grades cities using, in part, the EPA's color-coded Air Quality Index, as well as its own weighting system that ranks the severity of pollution on a daily basis.

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The city would give incentives to developers to clean up the kind of sites that fell in the light to mid-range of the pollution spectrum and thus languished in state and federal clean-up programs for their lack of severity: if developers complied with environmental guidelines and submitted to oversight, they would be spared the specter of future liability.

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In a sign of the growing severity of the problem, the new regulations published on Saturday describe "emergency measures" for days when pollution becomes a "danger to human health", including mandatory factory closures and restrictions on vehicles.

CNN: Beijing tries to clean up its act