Cal. Health and Safety Code § 40919

(a) Each district with serious air pollution shall, to the extent necessary to meet the requirements of the plan adopted pursuant to Section 40913, include the following measures in its attainment plan: (1) All measures required for moderate nonattainment areas, as specified in Section 40918. (2) A stationary source control program designed to achieve no net increase in emissions of nonattainment pollutants or their precursors from all new or modified stationary sources which emit, or have the potential to emit, 15 tons or more per year. The program shall require the use of best available control technology for any new or modified stationary source which has the potential to emit 10 pounds per day or more of any nonattainment pollutant or its precursors. (3) The use of the best available retrofit control technology, as defined in Section 40406, for all existing permitted stationary sources. (4) Measures to achieve the use of a significant number of low-emission motor vehicles by operators of motor vehicle fleets. (b) Any district with serious air pollution that has not met the criteria for a moderate classification by December 31, 1997, shall comply with Section 40920 if the state board demonstrates that the additional requirements of Section 40920 will substantially expedite the district’s attainment of the state ambient air quality standards. Any actions taken by the state board pursuant to this subdivision are subject to Section 41503.4.