Air Quality

Helping Us All to Breathe Easy


As the number of vehicles on the nation’s roadways increased, air pollution from mobile sources was identified as an important national health concern. Recognizing this connection, the 1990 Clean Air Act Amendments (CAAAs) and the Tennessee and Mississippi Transportation Conformity Rules require that transportation plans, programs (TIP), and projects conform to the Tennessee and Mississippi State Implementation Plans (SIPs). Conformity to a SIP means that planned transportation activities will not produce new air quality violations, worsen existing violations, or delay timely attainment of the National Ambient Air Quality Standards (NAAQS).

The Transportation Equity Act for the 21st Century (TEA-21) and its successor legislations, the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU), the Moving Ahead for Progress in the 21st Century (MAP-21), and the Fixing America’s Surface Transportation (FAST) Act, and most recently Infrastructure Investment and Jobs Act (IIJA) reinforce the need for coordinated transportation and air quality planning through the metropolitan planning process.

Transportation Conformity Determination

Transportation planners and air quality professionals conduct a transportation conformity analysis to estimate the effects of transportation projects and plans on air quality. The transportation conformity process is required of all MPOs within nonattainment areas – regions that the United States Environmental Protection Agency has determined do not meet air quality requirements.

To measure the impact of projects included in the RTP and TIP, an air quality conformity determination is conducted using the Environmental Protection Agency’s (EPA) Motor Vehicle Emissions Simulator, MOVES to demonstrate that the projects included in the current RTP/TIP conform to the appropriate air quality standards. The conformity determination must be made according to 40 CFR §93.105-(a)-(2) and (e) and the requirements of 23 CFR 450 (40 CFR §93.112, Criteria and Procedures).

A critical step involved in the air quality conformity determination is the review of the conformity analysis by the Interagency Consultation Committee (IAC), which serves as the MPO’s Air Quality Committee. The IAC reviews the procedures and results of the emission analysis and provides comments, which are included as part of the final analysis report. Details of the IAC process and the conformity process are provided in the Shelby County and DeSoto County Air Quality Conformity Demonstration Reports associated with the RTP and TIP.

Air Quality in the Greater Memphis Region

Currently, EPA designates Shelby County, Tennessee and DeSoto County, Mississippi as Attainment/Unclassifiable for the 2015 8-Hour Ozone NAAQS effective January 16, 2018 (Federal Register, Volume 82, Number 220 - 82 FR 54232).   There has been no ruling regarding the revocation of the Attainment/Maintenance area designation for Shelby and DeSoto County under the 2008 8-hour Ozone (O3) standard, therefore the Memphis MPO must demonstrate conformity for the 2008 8-hour ozone standard. 

The transportation conformity requirements, under the Clean Air Act (CAA) section 176(c), for the Memphis MPO carbon monoxide (CO) maintenance area, ended on December 26, 2017. 

EPA Transportation Conformity Requirements for Carbon Monoxide (CO) Letter

More Information

Project Related Conformity

For more information about project related conformity please visit the Regional Transportation Plan (RTP) and Transportation Improvement Program (TIP) webpages below;

Moving Together: 2050 RTP

FY 2023-26 TIP

Air Quality Index

To see how clean your outdoor air is, along with the associated health effects, visit EPA's AirNow Website. AirNow provides the Air Quality Index (AQI) and translates air quality data into numbers and colors that help people understand when to take action to protect their health. 

The U.S. Environmental Protection Agency, National Oceanic and Atmospheric Administration, National Park Service, tribal, state, and local agencies developed the AirNow system to provide the public with easy access to national air quality information. State and local agencies report the air quality index (AQI) for cities across the US and parts of Canada and Mexico.

AirNow data are used only to report the AQI and for informational purposes.

MPO Projects

Mid-South Regional Greenprint Plan

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GREENPRINT 2015/2040 is the final plan of the Mid-South Regional Greenprint and Sustainability Plan initiative, a process funded by a...

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In an effort to help shape future development along the I-269 Corridor in Tennessee, the Transportation Policy Board (TPB) of...

Poplar Southern Corridor Study

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The Southern/Poplar Corridor is a major east-west arterial roadway in Shelby County, TN. The corridor plays an important role as...

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A critical component of understanding future travel patterns and travel need throughout the Greater Memphis region is having a model...

Houston Levee Plan

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Houston Levee is an important north-south arterial roadway in the eastern part of Shelby County. It begins South of US-Hwy...

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