When the California Air Resources Board (ARB) initially established emissions criteria for replacement schoolbuses in 2008, the target for 2010 and newer model year school bus engines was 0.20 gram per brake horsepower-hour (g/bhp-hr) NOx and 0.01 g/bhp-hr particulate matter (PM) standards. However, due to the limited number of model year 2010 school buses that were manufactured and certified at or below the 0.20 g/bhp-hr NNOxOx emission levels, the NOx criterion for replacement school buses was changed to 0.50 g/bhp-hr.
Now ARB staff has determined that new school buses that meet a 0.20 g/bhp-hr NOx emission standard are readily available to purchase from the three school bus vendors in California.
Therefore, ARB is adjusting the NOx emission criterion. The maximum emission criteria for contracts executed through calendar year 2015 are 0.20 g/bhp-hr NOx and 0.01 g/bhp-hr PM, as originally intended.