HC+NOx emission standard: The numerical values of the applicable emission standards ere described in detail below and in section 91.207 of the regulatory text. As proposed in the SNPRM, EPA is finalizing an HC+NOx average emission standard which retains the 75 percent reduction in HC emissions and the 6.0 g/kw-hr NOx level in 2006 and later years proposed in the NPRM. This standard will take the form of an HC+NOx function that becomes more stringent each year for a nine year phase-in period. This function results from reducing baseline HC emissions to at most 25 percent of the uncontrolled level while allowing an increase of NOx from 2.0 to 6.0 g/kw-hr incrementally over nine years. Some NOx increase is technologically inevitable if HC reductions of 75 percent or more are to be achieved. The expected increase in total NOx emissions from these engines is small compared to the large HC inventory reductions.
The following formulas and tables summarize the HC+NOx emission standard for each rated power of the engine family as finalized for OB/PWC:
