From Wiki:
states may choose to follow either the national standard or the stricter California standards. States adopting the California standards include http://en.wikipedia.org/wiki/Arizona (2012 model year),http://en.wikipedia.org/wiki/United_States_emission_standards#cite_note-1 http://en.wikipedia.org/wiki/Connecticut, http://en.wikipedia.org/wiki/Maine, http://en.wikipedia.org/wiki/Maryland, http://en.wikipedia.org/wiki/Massachusetts, http://en.wikipedia.org/wiki/New_Jersey, http://en.wikipedia.org/wiki/New_Mexico (2011 model year), http://en.wikipedia.org/wiki/New_York, http://en.wikipedia.org/wiki/Oregon, http://en.wikipedia.org/wiki/Pennsylvania, http://en.wikipedia.org/wiki/Rhode_Island, http://en.wikipedia.org/wiki/Vermont, and http://en.wikipedia.org/wiki/Washington_%28U.S._state%29, as well as the http://en.wikipedia.org/wiki/Washington,_D.C..http://en.wikipedia.org/wiki/United_States_emission_standards#cite_note-Reuters20090630-2http://en.wikipedia.org/wiki/United_States_emission_standards#cite_note-3 Such states are frequently referred to as "CARB states" in automotive discussions because the regulations are defined by the http://en.wikipedia.org/wiki/California_Air_Resources_Board