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:

  • For tailpipe emissions: Motor Vehicle Emission Simulator model (currently MOVES2014a) is required for regional emissions analyses for transportation conformity determinations “regional conformity analyses” as of March 2, 2013 and for Project level “hot spot” analysis as of Dec. 20, 2012. The EPA released MOVES2014a in November, 2016. On August 28, 2018 the EPA released MOVES2014b, this is the latest version of MOVES that is required for regulatory transportation emissions analysis.
    • Official Release of the MOVES3 Motor Vehicle Emissions Model for State Implementation Plans and Transportation Conformity, effective January 7, 2021. This announcement starts a two-year transportation conformity grace period that ends on January 9, 2023.
  • 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.
  • For air quality dispersion models: The current EPA approved models for project level emissions analysis include either AERMOD Version 18081 updated April 24, 2018, or CAL3QHCR Version 13196 updated July 15, 2013.  The Arizona Department of Environmental Quality (ADEQ) provides Guidance for Air Quality Dispersion Modeling and pre-processed Meteorological Data on the ADEQ website.