Guidance - Air Quality
Guidance - Air Quality
Contents
Guidance
ADOT's Current Air Quality Guidance is provided below and will be updated as new information becomes available. For information related to Metropolitan Planning Organizations (MPOs) requirements refer to "The ADOT, MPO, and COG Guidelines and Procedures Manual", which is, intended to be a resource document to assist in outlining the guidelines and procedures to conduct regional transportation planning functions including regional transportation conformity.
Current Guidance in use for Congestion Mitigation Air Quality can be found on the "Congestion Mitigation Air Quality / Transportation Control Measures" webpage.
Project-Level Conformity
Project-Level conformity determinations for Environmental Assessments (EA) or Environmental Impact Statements (EIS) will be posted to Projects and/or be available from ADOT NEPA staff. Project-Level conformity determinations for Categorical Exclusion (CE) classified projects will be posted to "Transportation Conformity" for projects approved after January 3, 2018.
Note: These processes are currently under revision as CO conformity is no longer applicable in Arizona.
For Project-Level Conformity Hot-Spot Analysis: Any non-Exempt Federal Projects in PM10, PM2.5 maintenance and/or nonattainment areas may require a PM hot-spot analysis using the latest emissions models. Any modeling and planning assumptions used for transportation conformity project level hot-spots require interagency consultation, ADOT utilizes the document noted below for consultation, please contact ADOT Air Quality Staff for further information.
Motor Vehicle Emissions Modeling
Transportation conformity requires transportation plans, programs and projects in any nonattainment area for carbon monoxide, nitrogen dioxide, particulate matter, or ozone to evaluate air quality impacts before receiving Federal approval. The Arizona Department of Environmental Quality (ADEQ) submits air quality plans to the Environmental Protection Agency (EPA) that contains an emissions inventory of all sources that emit pollutants into the air. These air quality State Implementation Plans (SIPs) contain a cap on vehicle emissions, this limit on emissions is referred to as a Motor Vehicle Emissions Budget (MVEB). The EPA determines whether any MVEB established in an SIP is adequate for transportation conformity purposes; a list of approved budgets can be found on EPA's website.
The EPA also approves the type of emissions models that can be used to estimate transportation related emissions for a "regional conformity analysis" and project level "hot spot" analysis. ADOT Air Quality staff uses these models for regional and project level conformity analysis when necessary and also provides local agencies with specific motor vehicle registration data required to run these models, for more information contact [email protected].
Recent EPA Guidance on emissions models used for transportation:
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For tailpipe emissions: Motor Vehicle Emission Simulator model (currently MOVES5) is required for regional emissions analyses for transportation conformity determinations “regional conformity analyses” and for Project level “hot spot” analysis.
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Federal Register Notice of Availability: Official Release of MOVES5 Motor Vehicle Emissions Model for Emissions Inventories for SIPs and Transportation Conformity (pdf) This announcement starts a two year transportation conformity grace period that ends on December 11, 2026. After this date, MOVES5 will need to be used as the latest EPA emissions model for new transportation conformity analyses outside of California in both regional emissions analyses and in hotspot analysis.
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Federal Register Notice of Availability: Official Release of MOVES4 Motor Vehicle Emissions Model for Emissions Inventories in SIPs and Transportation Conformity (pdf)
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For re-entrained road dust: The EPA uses "AP-42: Compilation of Air Pollutant Emission Factors" to estimate road dust from paved and unpaved roadways. AP-42 Methods for Estimating Re-Entrained Road Dust from Paved roads 13.2.1 was updated on January 2011 and required for any conformity analysis Feb. 4, 2013. The current AP-42 Methods for Unpaved Roads can be found in section 13.2.2 last updated November 2006.
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For air quality dispersion models: The current EPA approved models for project level emissions analysis include either AERMOD & AERMET Version 23132 updated October 22, 2023, or CAL3QHCR Version 13196 updated July 15, 2013 only for CO modeling applications. The Arizona Department of Environmental Quality (ADEQ) provides Guidance for Air Quality Dispersion Modeling and pre-processed Meteorological Data on the ADEQ website.
Any modeling and planning assumptions used for transportation conformity project level hot-spots require interagency consultation, ADOT utilizes the document noted below for consultation, please contact [email protected]. for further information.
Transportation Control Measures
Under the Transportation Conformity Rule, Transportation Control Measures(TCMs) are strategies that are specifically identified and committed to in State Implementation Plans(SIPs), and are either listed in Section 108 of the Clean Air Act (CAA) or will reduce transportation-related emissions by reducing vehicle use or improving traffic flow.
Congestion Mitigation Air Quality
The Congestion Mitigation Air Quality (CMAQ) program is one source of funds for Transportation Control Measures (TCMs) employed for the purposes of reducing congestion and improving air quality.
More information on the CMAQ Improvement Program can be found at the Federal Highway Administration. The FHWA also provides a video summary of the CMAQ Program on their YouTube page. Annual Reports for all 50 States can be found in the FHWA CMAQ Public Access System (PAS) database
ADOT CMAQ Documents and Tools
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2024 CMAQ Program Interim Guidance (FHWA External Link)
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Contact [email protected] for more information