California Code, Health and Safety Code - HSC § 40447.6

(a) Notwithstanding any other provision of law, the south coast district board may, subject to the approval of the state board, adopt regulations that specify the composition of diesel fuel manufactured for sale in the south coast district. These regulations shall impose requirements at least as stringent as those of the state board. No regulation shall be adopted pursuant to this section until the south coast district has evaluated the safety of any fuel of a particular composition proposed to be required by the regulations. This section shall become operative January 1, 1989.

(b) In adopting regulations pursuant to this section, the south coast district board shall consider the effect of the regulation on emissions, public health, ambient air quality, and visibility in the south coast air basin; the technological feasibility and economic costs and benefits of the regulation compared to other available measures; and the availability of low emission and alternative fueled vehicles and alternative fuels.