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Air Quality

Air Quality Conformity

As the region's planning agency for transportation, SANDAG is required to demonstrate that transportation projects that receive state and federal funding will not adversely affect the region's air quality standards.

The Clean Air Act, which was last amended in 1990, requires the U.S. Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for pollutants considered harmful to public health and the environment. The Clean Air Act defines a 'nonattainment area' as a region where air pollution levels persistently exceed the NAAQS. The EPA requires that each state containing nonattainment areas develop plans for reaching attainment. These plans are called State Implementation Plans (SIP).

The Clean Air Act requires federally supported transportation activities to be consistent with the SIP. This requirement is referred to as transportation conformity. Conformity is to ensure that new transportation projects do not jeopardize air quality in nonattainment areas.

Conformity also is a way to ensure that federal funding and approval are given to those transportation activities that are consistent with air quality goals. Projects cannot be approved, funded, advanced through the planning process, or implemented unless those projects meet air quality standards.

SANDAG must demonstrate that the Regional Plan, which serves as the Regional Transportation Plan (RTP) for the San Diego region and the Regional Transportation Improvement Program (RTIP) are in conformity with the SIP for meeting air quality standards.

On April 15, 2004, the U.S. EPA designated the San Diego air basin as nonattainment for the 1997 Eight-Hour Ozone Standard. This designation took effect on June 15, 2004. In cooperation with SANDAG, the San Diego Air Pollution Control District (APCD) developed an Eight-Hour Ozone Attainment Plan for the 1997 standard, which was submitted to the U.S. EPA on June 14, 2007. The budgets in the Eight-Hour Ozone Attainment Plan for San Diego County were found adequate for transportation conformity purposes by the U.S. EPA, effective June 9, 2008.

However, on April 27, 2012, in response to a court decision, the U.S. EPA ruled that the San Diego basic nonattainment area be reclassified as a Subpart 2 moderate non-attainment area, with an attainment deadline of June 15, 2010. This reclassification became effective on June 13, 2012. Air quality data for 2009, 2010, and 2011 demonstrated that the San Diego air basin attained the 1997 ozone standard: APCD prepared a Maintenance Plan, with a request for redesignation to attainment/maintenance. On December 6, 2012, the California Air Resources Board (CARB) approved the Redesignation Request and Maintenance Plan for 1997 National Ozone Standard for San Diego County for submittal to U.S. EPA as a SIP revision. Effective July 5, 2013, U.S. EPA approved California’s request to redesignate the San Diego County ozone nonattainment area to attainment for the 1997 Eight-Hour Ozone National Ambient Air Quality Standard and their plan for continuing to attain the 1997 ozone standard for ten years beyond redesignation.

On May 21, 2012, the U.S. EPA designated the San Diego air basin as a non-attainment area for the 2008 Eight-Hour Ozone Standard and classified it as a marginal area with an attainment date of December 31, 2015. This designation became effective on July 20, 2012. SANDAG determined conformity to the new standard on May 24, 2013, using the model approved by U.S. EPA to forecast regional emissions (EMFAC2011). The U.S. DOT, in consultation with the U.S. EPA, made its conformity finding on June 28, 2013.  

Effective June 3, 2016, the U.S. EPA determined that 11 areas, including the San Diego air basin, failed to attain the 2008 ozone NAAQS by the applicable attainment date of July 20, 2015, and thus are reclassified by operation of law as “Moderate” for the 2008 ozone NAAQS. States containing any portion of these new Moderate areas must submit SIP revisions that meet the statutory and regulatory requirements that apply to 2008 ozone nonattainment areas classified as Moderate by January 1, 2017. The San Diego Air Pollution Control District submitted a SIP revision addressing Moderate area requirements to CARB on December 27, 2016. CARB submitted the SIP revision document to the U.S. EPA on April 12, 2017. Effective December 4, 2017, the U.S. EPA found the motor vehicle emissions budgets for the Reasonable Further Progress milestone year of 2017 from the 2008 Eight-Hour Ozone Attainment Plan for San Diego County adequate for transportation conformity purposes for the 2008 ozone NAAQS.

The San Diego region had been designated by the U.S. EPA as a federal maintenance area for the Carbon Monoxide (CO) standard. On November 8, 2004, CARB submitted the 2004 revision to the California SIP for CO to the U.S. EPA, which extended the maintenance plan demonstration to 2018. Effective January 30, 2006, the U.S. EPA approved this maintenance plan as a SIP revision. On March 21, 2018, the U.S. EPA documented in a letter that transportation conformity requirements for CO ceased to apply after June 1, 2018.

On October 9, 2015, the SANDAG Board adopted San Diego Forward: The Regional Plan (Appendix B)  and its air quality conformity. The U.S. DOT issued its conformity finding on December 2, 2015.

On September 28, 2018, the SANDAG Board of Directors adopted the final 2018 RTIP (see Chapter 5 and Appendices E and F) and its conformity determination and redetermination of conformity for San Diego Forward: The Regional Plan. The U.S. DOT, in consultation with U.S. EPA made its conformity determination on December 17, 2018.

Project Manager

Rachel Kennedy, Senior Regional Planner
Phone: (619) 699-1929, Email:

For media inquiries, please contact the SANDAG Public Information Office at (619) 699-1950 or