EPA designated the urban portion of the Fairbanks North Star Borough (FNSB) a nonattainment area for carbon monoxide (CO) in 1991. The FNSB has not violated the National Ambient Air Quality Standard (NAAQS) for carbon monoxide since 1999. EPA approved the FNSB's CO attainment plan and the FNSB officially became a Carbon Monoxide Maintenance Area on September 27, 2004.