One example was a tax for not purchasing emission control equipment for a car.

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But that could quickly change, thanks to improvements in emission control and America's recent switch to low-sulphur diesel.

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Rhodium, platinum and palladium are part of the platinum group metals (PGMs), primarily used to manufacture automobile emission control devices.

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"With limited data, human health risks are uncertain, states may design incorrect or ineffective emission control strategies, and EPA's decisions about regulating industry may be misinformed, " Elkins said.

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History suggests that such a perception is an invitation to aggression, making war more likely and adding further, albeit utterly unquantifiable costs to the potential bill associated with greenhouse gas emission control regimes.

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Tang Dagang, director of the Vehicle Emission Control Center, a policy research group also affiliated with the ministry, said pressure increased last year to tighten diesel fuel standards after the State Council, or cabinet, announced stricter air-quality rules.

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Corning's close relationship with Detroit, growing from its business of making automobile headlamps, has led to sales of ceramics for auto-emission-control devices.

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That change, called the Maximum Achievable Control Technology, or MACT, rule requires that coal- and oil-fired power plants reduce pollutant emission rates significantly.

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