(a) Districts with a population of one million residents or greater, in consultation with the state board, shall ensure that not less than 50 percent of the funds appropriated for purposes of the programs specified in paragraphs (1) to (3), inclusive, are expended in a manner that directly reduces air contaminants or reduces the public health risks associated with air contaminants in those districts, including, but not limited to, airborne toxics and particulate matter, in communities with the most significant exposure to air contaminants or localized air contaminants, or both, including, but not limited to, communities of minority populations or low-income populations, or both:

1. (1) The Carl Moyer Air Quality Standards Attainment Program (Chapter 9 (commencing with Section 44275) of Part 5 of Division 26 of the Health and Safety Code).
2. (2) Programs for the purchase of reduced-emissions schoolbuses.
3. (3) Diesel mitigation programs.