Tests by the EPA in 2004 of a E320 prototype indicated that the aftertreatment system came in at just beneath 0.06 g/mi of NOx; the Tier 2 Bin 5 target is 0.05 NOx g/mi. (See graph below)

The EPA has yet to sign off on urea-SCR systems for light-duty vehicles, partly due to concerns on enforcement. It is clear, however, that urea-SCR is going to be necessary to support a full 50-state rollout of most clean diesel vehicles. The EPA said at the recent DEER 2006 conference that it would soon provide guidance to manufacturers on urea-SCR systems for light-duty vehicles.