Cal. Health & Safety Code § 44299.54

On or before January 10, 2001, the executive officer of the state board shall make a determination as to the eligibility of NO x retrofit technologies for use in the program, and may make additional determinations of eligibility of NO x technologies after January 10, 2001. In order to be determined eligible by the executive officer of the state board, each NO x retrofit technology shall have, at a minimum, the ability to reduce onroad heavy-duty diesel emissions of NO x by 10 percent or more and shall be durable and effective in reducing emissions, as determined by the executive officer of the state board.