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Attainment Planning Using Emissions Analyses and Ozone Modeling

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  1. Summary
  2. Forums, reports and tools

Summary

To aid in evaluating the progress of existing emission control programs, assess the benefit of potential additional emissions control strategies, as well as to develop Attainment Demonstrations for RAQC region residents and U.S. EPA in accordance with State Implementation Plan (SIP) requirements, the RAQC engages in emissions analyses and photochemical modeling efforts. Photochemical modeling estimates the effects of emissions on ambient air quality using a grid-based computer model that simulates air pollution episodes impacting the entire RAQC region. The modeling tool is first used to replicate a recent historical year’s ozone monitoring data with modeling results using historic emissions data. It then estimates the air quality changes for a future milestone year by holding meteorology and out-of-area emissions constant while studying reductions of local emissions. It is the most effective tool available and is EPA-required for determining the cause of serious air pollution problems and what local emissions can be reduced to improve regional air quality. Photochemical modeling allows for the assessment of:

  • How sensitive pollutants are to varying parameters such as meteorological conditions and emission rates
  • How sensitive pollutants are to control scenarios
  • Efficacy of proposed control strategies

Photochemical modeling is completed using EPA-approved modeling platforms and methodologies. For attainment planning modeling efforts, a detailed modeling protocol is developed that outlines the technical details of the emissions to be estimated and air quality modeling to be performed. The protocol documents the approach, procedures, participants, and other requirements needed to conduct photochemical grid modeling. This page provides references, tools, and reports that have been developed to support the RAQC’s ongoing emissions analysis and air quality modeling efforts.

For more information on air emissions modeling, please see EPA’s air emissions modeling, emissions inventories, and photochemical air quality modeling pages.

Forums, reports and tools

Forums are dedicated RAQC meetings where methodologies, analyses, and results related to technical modeling and analysis work needed to support the SIP process and attain the ozone standards are discussed in-depth. They cover a wide range of topics, from how the model is selected to how the model demonstrates the effects of local, regional, and international sources on ozone and how attainment is monitored. Below are references to forums previously conducted by the RAQC, with each forum link containing relevant documents and resources.

  1. December 12, 2025 Forum

    This forum will focus on how to use the Source Apportionment and DDM dashboards available in the next dropdown box on this page.

  2. October 30, 2025 Forum

    Topics covered

    • Update on Planning and Control Strategy Development
    • Overview of Modeling Work and 2026 Modeled Design Value Projections
    • 2026 Ozone Source Apportionment Method and Results
    • 2026 Direct Decoupled Method Modeling Analysis Methodology
    • DM/NFR Oil & Gas Emission Inventory Scenarios for Ozone Air Quality Planning

  3. July 25, 2025 Forum

    Postponed, rescheduled for October 30th.

  4. April 30, 2025 Forum

    Topics covered

    • RAQC Control Strategy Development Updates
    • Ozone Air Quality, Emissions, and Modeling Results: Effects on Planning
    • 2026 Oil and Gas Modeling Projections Emissions Inventory Effort
    • Modeling Platform Development Comprehensive Overview

  5. October 22, 2024 Forum

    Topics covered

    • RAQC Planning, Analysis, and Control Strategy Updates
    • Ozone Modeling Schedule and Status Updates
    • 2024 Ozone Season Data Report and Attainment Planning Effects
    • 2022 Emission Inventories

  6. July 18, 2024 Forum

    Topics covered

    • Bump-up of the 2015 Ozone NAAQS Nonattainment Area to the Serious Classification
    • 2024 Ozone Season Data Report and Planning Considerations
    • Timeline and Milestones for Attainment Planning
    • Status of technical work on Emissions and Modeling

  7. April 23, 2024 Forum

    Topics covered

    • Draft Conceptual Model of Ozone Formation in the DM/NFR Non-attainment Area
    • Emissions Inventory Improvements and Controls Presentation
    • SIP Modeling Protocol

  8. October 26, 2023 Forum

    Topics covered

    • Severe 75 ppb and Moderate 70 ppb SIP modeling – Results and Lessons Learned
    • Emissions, Control Strategy, and Modeling Plans for the Serious 70 ppb SIP planning effort during 2024-25

  9. May 12, 2023 Forum

    Topics covered

    • Methodology Outline: Denver Metro/North Front Range Oil and Gas Emission Inventory, May 10, 2023
    • Revised Oil and Gas Emission Inventory Results
      • 2017 Oil and Gas Emission Inventory Spreadsheets, April 28, 2023
      • 2026 Oil and Gas Emission Inventory Spreadsheets, May 10, 2023
    • Severe SIP Modeling Plan

  10. May 18, 2022 Forum

    Topics covered

    • 2016 Modeling Platform Update since April 2021
    • Analysis of 2020 and 2021 Meteorology
    • 2023 and 2026 Design Value Projections
    • Planned and Potential Sensitivity Analyses

  11. April 14, 2021 Forum

    Topics covered

    • 2016 Modeling Platform Update
    • 2023 NOx/VOC Sensitivity Analysis
    • 2023 Local Source Modeling
    • 2023 International and Interstate Transport Analysis

  12. June 4, 2020 Forum

    Topics covered

    • Development of 2016 Base Case Modeling
    • 2020 and 2023 Future Year Modeling Projections

  13. November 2, 2017 Forum

    Topics covered

    • Overview of Modeling Sensitivities
    • 2017 Local Source Apportionment Modeling
    • Contribution of International Emissions on 2011 Base Case
    • 2023 Ozone Projections and NOx/VOC Sensitivity
    • FRAPPE and DISCOVER-AQ 2014 Regional Source Impacts
    • Comparison of Oil and Gas Inventories with Monitored Ambient VOC Precursors

  14. August 9, 2012 Forum

    Topics covered

    • Development of 2008 Base Case Model
    • Ozone Model Evaluation for the Denver 2008 Episode

The RAQC is conducting modeling efforts to aid in planning and SIP development efforts under the 2015 8-hour ozone Standards. Below are currently available reports and tools developed in support of this effort.

Two DDM modeling dashboards to download and explore the data and results (October 2025):

Four source apportionment modeling dashboards to download and explore the data and results (October 2025):

Reports and reference documents:

This is an overview of the Version 1 platform data and information described in more detail below. The 2022v1 Technical Support Document is posted on the EPA 2022v1 web site: 2022v1 Emissions Modeling Platform | US EPA. EPA added a spreadsheet version of the 2022v1 comments to the web page: https://gaftp.epa.gov/Air/emismod/2022/v1/reports/comments_responses/. Version 1 data for 2022 actual emissions and 2026 projections from 2022 provide large amounts of key data needed to complete the Denver Metro / North Front Range Ozone NAAQS Plan Modeling.

The RAQC is conducting modeling efforts to aid in planning and SIP development efforts under the 2008 8-hour ozone Standards. Below are currently available reports and tools developed in support of this effort.

Reports and tools developed in support of prior modeling efforts are detailed below:

Guidance documents from the EPA recommend steps to conduct modeling for ozone nonattainment areas. Generally, the guidance comes in two parts. The first part includes how to set up and apply a photochemical modeling platform, which includes meteorology, emissions, and air quality modeling. The second part describes how to use the modeling platform to project future year concentrations and demonstrate whether attainment of the standard is likely.

The RAQC puts out requests for services from a consulting firm to aid in completing the modeling recommended under EPA guidance.