In the absence of an approved State Implementation Plan (SIP), a plan prepared by the US EPA that provides measures that nonattainment areas must take to meet the requirements of the Federal Clean Air Act
California Air Resources Board ARB (California Environmental Protection Agency), glossary of air pollution terms, Sacramento, CA, USA 2013. http://www.arb.ca.gov/html/gloss.htm, (Air Pollut - Amer) {594}