The Clean Air Act regulates ozone as a criteria pollutant. The U.S. EPA sets National Ambient Air Quality Standards for ozone, including both primary standards to protect public health and secondary standards to protect the environment. The first ozone standard was published in 1979. The standard was 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. The revisions to the standard in 2008 and 2015 each lowered the level of the standard, but they were still based on eight-hour average concentrations.

The accordions for the ozone standards below include the relevant documents associated with the boundary designations and the state implementation plan elements developed for each of the standards.

2015 Standard

8-hr Ozone Standard: 70 parts per billion, or ppb

Boundary Recommendations

2015 Standard Boundary Recommendations Actions Table

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 4, 2018

Final Boundary Designations for the 2015 Ozone NAAQS (remaining area):

[83 FR 25776]
Effective Date 08/03/18

Sept. 22, 2017 Letter to EPA on 2015 Ozone Recommendations April 30, 2018 EPA Designation Letter to Governor - Completed Designations for the 2015 8-hour ozone standard
Dec. 20, 2017 EPA 120-day Letter - for the Second Round Designations under the 2015 8-hour ozone standard
Sept. 30, 2016

2015 Ozone Standard Area Boundary Designation Recommendation

Nov. 16, 2017

Final Boundary Designations for the 2015 Ozone NAAQS (most areas):

[82 FR 54232]
Effective Date 01/16/18

Nov. 6, 2017 EPA Designation Letter to Governor - Initial Round Designations for the 2015 8-hour ozone standard

Infrastructure SIP

2015 Standard Infrastructure SIP Actions Table

MoDNR Submittal Date MoDNR Action/Document EPA Date EPA Action/Document
June 17, 2022 Air Program Comment Letter on EPA Proposed Federal Good Neighbor Plan for the 2015 Ozone Standard April 6, 2022 EPA Proposed Consent Decree [87 FR 20036]
April 22, 2022 Air Program Comment Letter on Federal Proposed Disapproval of Missouri's Good Neighbor Plan for the 2015 Ozone Standard, April 22, 2022 Feb. 2, 2022 Proposed Disapproval of Missouri's Good Neighbor Plan [87 FR 9533]
Nov. 8, 2021 Air Program Comment Letter on Proposed Consent Decree Oct. 15, 2021 EPA Proposed Consent Decree [86 FR 57423]
June 10, 2019

Interstate Transport Provisions for the 2015 Ozone Standard

Pending

Pending

April 11, 2019 Infrastructure Elements for the 2015 Ozone Standard Sept. 30, 2019

Approval [84 FR 51413]

St. Louis Area

2015 Standard St. Louis Area Actions Table

MoDNR Submittal Date MoDNR Action/Document EPA Date EPA Action/Document
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 - St. Louis 2015 Ozone Standard

Implementation Impact Report

Pending Pending

2008 Standard

8-hr Ozone Standard: 75 parts per billion, or ppb

Boundary Recommendations

2008 Standard Boundary Recommendations Actions Table

MoDNR Submittal Date MoDNR Action/Document EPA Date EPA Action/Document
Dec. 8, 2011

Revised 2008 8-hr Ozone Boundary Recommendation

May 21, 2012

Final Boundary Designations for 2008 Ozone NAAQS

[77 FR 20088]

Effective Date 07/20/12

March 11, 2019 Original 2008 Ozone Boundary Recommendation Letter Dec. 8, 2011

EPA 120-day letter for the 2008 Ozone Standard

Attachment to EPA 120-day Letter

Support Document - Original 2008 Ozone Boundary Recommendations

Infrastructure SIP

2008 Standard Infrastructure SIP Actions Table

MoDNR Submittal Date MoDNR Action/Document EPA Date EPA Action/Document
July 1, 2013

Section 110 Infrastructure SIP for the 2008 Ozone NAAQS

Sept. 24, 2017

Approval of Element 110(a)(2)(D)(i) prong 4

[83 FR 48242]

March 22, 2018

Approval of all elements except 110(a)(2)(D)(i) prong 1, 2 and 3

[83 FR 12496]

Oct. 26, 2016 Federal Plan for elements 110(a)(2)(D)(i) prong 1 and 2 (CSAPR Update)

[81 FR 74504]

St. Louis Area

2008 Standard St. Louis Area Actions Table

MoDNR Submittal Date MoDNR Action/Document EPA Date EPA Action/Document
Nov. 12, 2019 Maintenance Plan Revisions for the St. Louis (Missouri) Maintenance Area Under the 1979, 1997 and 2008 Ozone Standard Sept. 30, 2021

Sept. 30, 2021

Approval - Maintenance Plan Revision

[86 FR 54098]
Effective Date 11/01/21

Feb. 16, 2018 Technical Correction to the Redesignation Request and Maintenance Plan for the St. Louis 2008 Ozone Standard Sept. 20, 2018

Approval - Maintenance Plan and Redesignation

[83 FR 47572]
Effective Date 09/20/18

July 27, 2017

Supplement - Redesignation Request and Maintenance Plan-Discussion of Emissions

Sept. 20, 2018

Approval - Maintenance Plan and Redesignation

[83 FR 47572]
Effective Date 09/20/18

Nov. 21, 2016 Clarification Letter - on Redesignation and Maintenance Plan Sept. 20, 2018

Approval - Maintenance Plan and Redesignation

[83 FR 47572]
Effective Date 09/20/18

Sept. 12, 2016

Original - St. Louis 2008 Ozone Maintenance Plan

Sept. 20, 2018

Approval - Maintenance Plan and Redesignation

[83 FR 47572]
Effective Date 09/20/18

Sept. 4, 2014

Marginal Nonattainment Area Plan - St. Louis 2008 Ozone Standard

Feb. 25, 2016

Approval - Marginal Area Plan

[81 FR 9346]

Aug. 16, 2013 Early Progress Plan - St. Louis 2008 Ozone Standard Nonattainment Area Jan. 14, 2016

Approval - Early Progress Plan

[81 FR 1887

Related Links

Weekly Summary of Monitored Ozone Values

If you are looking for a document that is not available on our website, please submit a Sunshine Law Request.