Despite a staff recommendation to relax the more stringent NOx emission standards for urban buses to match federal limits for the period from 2007 to 2010 (earlier post), the California Air Resources Board voted unanimously Thursday to maintain the standard at its current level.
Under current regulations, urban buses must meet a 0.2 g/bhp-hr standard for NOx emissions starting in 2007. The California standard for truck engines, and the federal standard, are both 1.2 g/bhp-hr in 2007. In 2010, trucks and buses, in California and under EPA regulations, all must meet the more stringent 0.2g/bhp-hr standard.
Because ARB believes that diesel manufacturers will not be able to meet the more stringent standard in 2007, it faced the situation of having transit agencies which had opted for diesel platforms not being able to purchase any new buses for those three model years.
The board considered three options: leave the standard unmodified, adjust the standard to the 1.2 gram number, or mandate all agencies to purchase alternative fuel buses (which will meet the 0.2g standard in 2007. ARB staff recommended the second option.
The Board, however, decided that relaxing the standard would send the wrong message, and chose the first option, with a modification.
Transit agencies will be able to purchase diesel buses that exceed the standard, but only if they offset the additional emissions by retrofitting older diesel with NOx control devices.
UPDATE: ARB has scheduled a continuation to October 27 on the matter to provide ARB staff with the opportunity to review and to report to the Board the impact of the Board’s decision to retain the urban bus standard of 0.2 g/bhp-hr NOx on transit agency’s Carl Moyer funding. At the October 27 meeting, the Board may reconsider its decision to retain the heavy-duty urban bus engine NOx standard in light of the staff’s report.