The Clean Air Act regulates ozone as a criteria pollutant. The U.S. Environmental Protection Agency (EPA) sets National Ambient Air Quality Standards for ozone (O3). These standards include both primary standards to protect public health and secondary standards to protect the environment. EPA reviews pollutant standards every five years. Sometimes, a review results in a tightened standard. The first ozone standard was published in 1979 and based on one-hour average concentrations. In 1997, EPA revised the ozone standard based on eight-hour average concentrations. In 2008, and again in 2015, EPA revised the ozone standard. Both revisions lowered the standard level, but were still based on eight-hour average concentrations.
The ozone standards below include the state implementation plan elements developed for each of the standards and the relevant documents associated with the boundary designations. If you are looking for a document that is not available on our website, please submit a Open Records/ Sunshine Law Request.
- 2015 Standard
8-hr Ozone Standard = 70 parts per billion (ppb)
2015 Standard Boundary Recommendations Actions| MoDNR Submittal Date | MoDNR Action/Document | EPA Date | EPA Action/Document |
|---|
| Feb. 16, 2018 | Revision to Area Boundary Designation Recommendation for the 2015 Ozone Standard | June 14, 2021 | Revised Air Quality Designations for the 2015 Ozone National Ambient Air Quality Standards (Jefferson County) [86 FR 31438] |
| June 4, 2018 | Additional Air Quality Designations for the 2015 Ozone National Ambient Air Quality Standards (remaining area) [83 FR 25776]
Effective: Aug. 3, 2018 |
| Sept. 22, 2017 | MoDNR Letter to EPA Requesting No Action on 2015 Ozone Recommendations | April 30, 2018 | EPA Letter to Governor Regarding Area Designations for the 2015 Ground-level Ozone National Ambient Air Quality Standards - Completes area designations for the 2015 ozone standard |
| Dec. 20, 2017 | EPA Response to Recommendations on Designations for the Revised 2015 National Ambient Air Quality Standards for Ozone - 120-day letter for the second round designations under the 2015 ozone standard |
| Sept. 30, 2016 | 2015 Ozone Standard Area Boundary Designation Recommendation | Nov. 16, 2017 | Air Quality Designations for the 2015 Ozone National Ambient Air Quality Standards (NAAQS) (most areas) [82 FR 54232]
Effective: Jan. 16, 2018 |
| Nov. 6, 2017 | EPA Letter to Governor Regarding 2015 Ground-level Ozone Standards Met - Initial round designations for the 2015 ozone standard |
2015 Standard Infrastructure SIP Actions| MoDNR Submittal Date | MoDNR Action/Document | EPA Date | EPA Action/Document |
|---|
| Oct. 18, 2024 | MoDNR Comment Letter on EPA Proposed Rule: Air Plan Partial Disapproval; Missouri Interstate Transport of Air Pollution for the 2015 8-Hour Ozone National Ambient Air Quality Standards | Aug. 6, 2024 | Air Plan Disapproval; Missouri; Interstate Transport of Air Pollution for the 2015 8-Hour Ozone National Ambient Air Quality Standards [89 FR 63830] |
| Nov. 1, 2022 | Supplement to the Interstate Transport Provisions for the 2015 Ozone Standard | Pending | Pending |
| June 17, 2022 | MoDNR Comment Letter on EPA Proposed Rule: Federal Implementation Plan Addressing Regional Ozone Transport for the 2015 Ozone National Ambient Air Quality Standard | April 6, 2022 | Federal Implementation Plan Addressing Regional Ozone Transport for the 2015 Ozone National Ambient Air Quality Standard [87 FR 20036] |
| April 22, 2022 | MoDNR Comment Letter on EPA Proposed Rule: Air Plan Disapproval; Missouri Interstate Transport of Air Pollution for the 2015 8-Hour Ozone National Ambient Air Quality Standards | Feb. 2, 2022 | Air Plan Disapproval; Missouri Interstate Transport of Air Pollution for the 2015 8-Hour Ozone National Ambient Air Quality Standards [87 FR 9533] |
| Nov. 8, 2021 | MoDNR Comment Letter on Federal Register Action: Proposed Consent Decree, Clean Air Action Citizen Suit | Oct. 15, 2021 | Proposed Consent Decree, Clean Air Act Citizen Suit [86 FR 57423] |
| June 10, 2019 | Interstate Transport Provisions for the 2015 Ozone Standard | Feb. 13, 2022 | Air Plan Disapprovals; Interstate Transport of Air Pollution for the 2015 8-Hour Ozone National Ambient Air Quality Standards [88 FR 9336] |
| April 11, 2019 | Infrastructure Elements for the 2015 Ozone Standard | Sept. 30, 2019 | Air Plan Approval; Missouri; Infrastructure State Implementation Plan Requirements for the 2015 Ozone National Ambient Air Quality Standard [84 FR 51413] |
2015 Standard St. Louis Area Actions| MoDNR Submittal Date | MoDNR Action/Document | EPA Date | EPA Action/Document |
|---|
| Sept. 6, 2023 | MoDNR Submittal of St. Louis Moderate Nonattainment Area Plan for the 2015 Ozone Standard | Pending | Pending |
| April 21, 2023 | MoDNR Comment Letter on Federal Register Action: Draft Guidance on the Preparation of State Implementation Plan Provisions | March 23, 2023 | Draft Guidance on the Preparation of State Implementation Plan Provisions that Address the Nonattainment Area Contingency Measure Requirements for Ozone and Particulate Matter [88 FR 15571] |
| | | Oct. 7, 2022 | Determinations of Attainment by the Attainment Date, Extensions of the Attainment Date, and Reclassification of Areas Classified as Marginal for the 2015 Ozone National Ambient Air Quality Standards [87 FR 60897] |
| April 8, 2022 | Maintenance Plan for the St. Louis Nonattainment Area for the 2015 Ozone Standard | Pending | Pending |
| April 8, 2022 | Redesignation Request for the St. Louis Nonattainment Area for the 2015 Ozone Standard | Pending | Pending |
| Sept. 8, 2021 | Marginal Nonattainment Area Plan for the Missouri Portion of the St. Louis Nonattainment Area Under the 2015 Ozone Standard Implementation Impact Report: Marginal Nonattainment Area Plan for the Missouri Portion of the St. Louis Nonattainment Area for the 2015 Ozone Standard | Feb. 7, 2023 | Air Plan Approval; MO; Marginal Nonattainment Plan for the St. Louis Area for the 2015 8-Hour Ozone Standard [88 FR 7885] |
- 2008 Standard
8-hr Ozone Standard = 75 parts per billion (ppb)
2008 Standard Infrastructure SIP Actions| MoDNR Submittal Date | MoDNR Action/Document | EPA Date | EPA Action/Document |
|---|
| July 1, 2013 | Section 110 Infrastructure Requirements for the 2008 Ozone National Ambient Air Quality Standard (NAAQS) | Sept. 24, 2017 | Air Plan Approval; Missouri; Regional Haze Plan and Prong 4 (Visibility) for the 2012 PM2.5, 2010 NO2, 2010 SO2, and 2008 Ozone NAAQS [83 FR 48242] |
| March 22, 2018 | Approval of Implementation Plans; State of Missouri; Elements of the Infrastructure State Implementation Plan Requirements for the 2008 Ozone, 2010 Nitrogen Dioxide, 2010 Sulfur Dioxide, and 2012 Fine Particulate Matter National Ambient Air Quality Standards (NAAQS) [83 FR 12496] |
| Oct. 26, 2016 | Cross-State Air Pollution Rule Update for the 2008 Ozone NAAQS [81 FR 74504] |
2008 Standard St. Louis Area Actions| MoDNR Submittal Date | MoDNR Action/Document | EPA Date | EPA Action/Document |
|---|
| Nov. 12, 2019 | Maintenance Plan Revision for the St. Louis (Missouri) Maintenance Area under the 1979, 1997, and 2008 Ozone Standards | Sept. 30, 2021 | Air Plan Approval; Approval of Missouri Air Quality Implementation Plans; Revisions to St. Louis 2008 8-Hour Ozone Maintenance Plan [86 FR 54098]
Effective: Nov. 1, 2021 |
| Feb. 16, 2018 | Technical Correction to the Redesignation Request and Maintenance Plan for the St. Louis (Missouri) 2008 Ozone Standard Nonattainment Area | Sept. 20, 2018 | Approval of Missouri Air Quality Implementation Plans; Redesignation of the Missouri Portion of the St. Louis-St. Charles-Farmington, MO-IL 2008 Ozone Area to Attainment [83 FR 47572] |
| July 27, 2017 | 2008 Ozone Redesignation Request Maintenance Plan Discussion of Emissions |
| Nov. 21, 2016 | MoDNR Clarification Letter Regarding Redesignation Request and Maintenance Plan for the St. Louis (Missouri) 2008 Ozone Standard Nonattainment Area |
| Sept. 12, 2016 | Redesignation Request and Maintenance Plan for the St. Louis (Missouri) 2008 Ozone Standard Nonattainment Area |
| Sept. 4, 2014 | Marginal Area Plan for the Missouri Portion St. Louis Nonattainment Area for the 2008 8-hour Ground-Level Ozone National Ambient Air Quality Standard | Feb. 25, 2016 | Approval and Promulgation of Air Quality Implementation Plans; State of Missouri; Emissions Inventory and Emissions Statement for the Missouri Portion of the St. Louis MO-IL Ozone Nonattainment Area [81 FR 9346] |
| Aug. 16, 2013 | Early Progress Plan for the Missouri Portion of the St. Louis Nonattainment Area for the 2008 Ozone National Ambient Air Quality Standard | Jan. 14, 2016 | Approval of Missouri’s Air Quality Implementation Plans; Early Progress Plan of the St. Louis Nonattainment Area for the 2008 Ozone National Ambient Air Quality Standard [81 FR 1887] |
