The South Coast Air Quality Management District (District) is charged with regulating nonvehicular air pollution emissions in a large area that encompasses much of Los Angeles and other parts of Southern California, regions that have some of the worst air pollution in the country. This case concerns the District‟s 2002 amendments to its Rule 1113, which limits certain pollution-causing substances in paints and coatings. The American Coatings Association (Association) challenged the amendments on the ground that they exceeded the District‟s regulatory authority under statutes requiring the use of “best available retrofit control technology.” According to the Association, the District failed to show that technology necessary to meet the emissions limits set by the 2002 amendments was “available” within the meaning of the relevant statutes. Plaintiffs challenged the rule, which set strict limits for VOC s for several categories of paints and coatings to be phased in over time. They argued that the limits were not achievable for many products and applications within a given category. The issue was whether the “best available retrofit control technology” provision in section 40440 of the California Health and Safety Code limits airdistrict authority to the adoption of rules requiring existing technology. In 2009, an appellate court held that SC AQMD had failed to show that the technology necessary to meet the emissions limit set by 2002 amendments to Rule 1113 was “available” within the meaning of relevant statutes. Rejecting that decision, the state supreme court held that SC AQMD has “the authority to promulgate pollution standards based on technologies that do not currently exist but are reasonably anticipated to exist by the compliance deadline.”