ARB Staff Recommends Relaxing California Bus NOx Standards to Match EPA 2007

20 October 2005

Results of the 3 options

The staff of the California Air Resources Board has recommended an adjustment of California’s more stringent NO_x 2007 emissions standards for urban buses to be in alignment with the federal EPA standards.

The recommendation came during a public meeting over the issue that has stirred considerable anxiety among transit agencies and engine manufacturers.

ARB has been struggling with a dilemma. California NO_x emissions requirements for urban buses in 2007 are more stringent than those of the EPA, requiring 0.2 g/bhp-hr as opposed to the 1.2 g/bhp-hr of the EPA. But CARB began to doubt, based on their discussions with diesel engine manufacturers, that achieving this 0.2 g/bhp-hr level of NOx emissions from diesel engines in 2007 is possible.

In 2010, both sets of standards align on the 0.2 figure, so presumably the problem won’t exist then. But without some sort of corrective action, California transit agencies would face a situation where they could be precluded from purchasing new diesel buses for three model years (2007, 2008 and 2009).

Earlier this summer, CARB came up with three possible solutions (earlier post):

1. Keep the current new urban bus emissions standards as they are. Diesel agencies would buy no new diesel for MY 2007–2009, and make up for those deferred purchases in 2010–2012 when diesel engines are again available.

2. Realign the NOx emission standard for 2007 through 2009 model year new urban buses with the federal standard by raising it from 0.2 g/bhp-hr to 1.2 g/bhp-hr.

3. Require all transit agencies to purchase/lease only alternative fuel buses, as alternative fuel buses will meet the 0.2g requirement in 2007. This option would mandate that at least 85% of a transit agency’s annual purchases be alternative-fueled through 2015.

It was the possibility of the final option that sent transit agencies that had been working on upgrading their diesel fleets and diesel engine manufacturers through the roof.

After evaluating the likely outcomes of the different scenarios (graph at top), ARB staff today recommended option 2—relaxing the California standards to match the federal standards which the diesel engine makers will be able to meet. For fleets larger than 30, ARB staff is recommending some extra NO_x mitigation.

The Board will vote on the recommendation Thursday or Friday.

Resources:

• Urban Bus New Engine Emission Standards