California Code, Health and Safety Code - HSC § 44062.2

(a) The state board shall adopt, by regulation, procedures to establish an emissions credit exchange program whereby persons may contribute to the Vehicle Inspection, Repair, and Retrofit Fund, and receive equitable emission reduction credits for those contributions.

(b) Districts may establish procedures to generate marketable emission reduction credits from contributions toward the repair subsidy and vehicle retrofit subsidy program specified in Section 44062.1. Emission reduction credits generated pursuant to this subdivision may be used to meet or offset transportation control measure requirements, average vehicle ridership reductions, or other mobile source emission requirements, as determined by the district.

(c) In federal nonattainment areas, the credits established pursuant to subdivision (a) or (b) shall be allowed only for emission reductions that are in excess of the reasonable further progress goals established by Section 182 of the amendments enacted in 1990 to the Clean Air Act (P.L. 101-549)  1, or in excess of alternative progress goals established in a state implementation plan pursuant to Section 182 of the Clean Air Act.

(d) This section shall become inoperative five years from the date determined pursuant to Section 32 of the act adding this subdivision, and on the January 1 following that date is repealed.