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The US states with the most stringent emissions requirements β€” California, Maine, Massachusetts, New York and Vermont β€” say Mercedes's E320 Bluetec is not clean enough for prime time. That's a kick in the tailpipe to Merc, which in a recent press release called the E320 CDI the "cleanest diesel vehicle in the world." The problem is, diesel generates more nitrogen oxide gases than gas engines, and although Mercedes's Bluetec system uses a combination of scrubbers in the car's exhaust system β€” an oxidizing catalytic converter, a particulate filter and a denox storage converter that absorbs nitrogen oxides temporarily β€” it's just not quite enough. The company also has a separate system, called AdBlue, that injects urea (yeah, that one) into the exhaust, splitting nitrogen oxides into hydrogen and H20, but that system isn't commercially available. What does the blow mean for Mercedes, which needs to sell the E-Class diesel in those states to make a viable business case? No word yet, but a spokesperson reportedly said, "piss off."

Snafu: New Mercedes Diesels Ruled Illegal in Five Key States [Edmunds]

Mercedes-Benz E320 BLUETEC Debuts in New York; More Diesels for US Lineup [Green Car Congress]

Mercedes Reveals 2007 E-Class [internal]