Ground-level ozone, best known as smog, is an air pollutant seen primarily in the summer and fall which can inhibit breathing and damage respiratory systems at higher concentrations. Breathing ozone is akin to giving your lungs a sunburn: the pollutant damages healthy cells and prolonged exposure can lead to serious health impacts.
Ozone levels in Yolo-Solano are in the healthy range on most days. However, ozone and its precursors don’t respect political boundaries, and emissions created within Yolo and Solano counties may affect neighboring communities, especially in the greater Sacramento region. As such, the Yolo-Solano AQMD is included in the Sacramento Federal Non-attainment Area (SFNA) by the U.S. Environmental Protection Agency (EPA).
The U.S. EPA periodically reviews its National Ambient Air Quality Standards (NAAQS) for regulated pollutants. The EPA may also revise its standards when health studies indicate that a revision is necessary to protect the most sensitive segments of the population.
2015 NAAQS; 8-hour standard of 0.070 ppm (70 ppb)
| Document | Date | Description |
| Proposed Contingency Measures and Reasoned Justification | October 9, 2024 | Each of the SFNA air districts will adopt the contingency measure analysis (for the 2008 and 2015 standards) and submit the SIP update to ARB for submittal to EPA. The Yolo-Solano Board adopted the analysis on October 9, 2024. |
| Sacramento Regional 2015 NAAQS 8-Hour Ozone Attainment & Reasonable Further Progress Plan | November 17, 2023 | Each of the SFNA air districts adopted the plan in the fall of 2023 and submitted the Plan to the California Air Resources Board (ARB) who submitted it to the US EPA on November 17, 2023 for approval. |
| Base year emissions inventory | September 29, 2022 | EPA approved California’s Non-attainment Areas base year emissions inventory (87 FR 59015) |
| Non-attainment New Source Review (NNSR) certification | June 9, 2021 | Our Governing Board certified that our existing New Source Review rule 3.4 meets the requirements for the 2015 standard on June 9, 2021, and it has been submitted to ARB who submitted it to US EPA. |
| Reasonably Available Control Technology (RACT) SIP Analysis | September 9, 2020 | The Federal Clean Air Act (CAA), Part D, Section 182(b)(2) requires ozone non-attainment areas to implement RACT for certain categories of sources. |
| Emissions Statement Certification | September 9, 2020 | Yolo-Solano’s Governing Board certified that our existing Emissions Statement Rule 3.18 in the SIP (renumbered locally to Rule number 3.7) meets the CAA section 182(a)(3)(B) requirements for the 2015 ozone standard. EPA published approval on July 29, 2022 (87 FR 45657). |
| Severe Bump Up | July 26, 2022 | The districts in the SFNA sent a request to ARB to voluntarily reclassify from serious to severe, with an attainment date of August 3, 2033. |
| Serious Bump Up | May 26, 2020 | The districts in the SFNA sent a request to ARB to voluntarily reclassify from moderate to serious. On August 3, 2020 ARB submitted this request to EPA. On October 28, 2021 EPA published a final rule in the Federal Register (86 FR 59648) approving the reclassification. |
| Moderate Designation | June 4, 2018 | In 2016, the California Air Resources Board (ARB) recommended in their report that the SFNA be designated non-attainment (based on 2014-2016 monitoring data). The EPA published a final rule on June 4, 2018 (83 FR 25776) designating the Sacramento Metro area as moderate non-attainment. |
| Standard promulgated | October 1, 2015 | EPA revised the 8-hour ozone standard, lowering it from 0.075 ppm to 0.070 ppm (80 FR 65292) |
2008 NAAQS; 8-hour standard of 0.075 ppm (75 ppb)
| Document | Date | Description |
| Proposed Contingency Measures and Reasoned Justification | October 9, 2024 | Each of the SFNA air districts will adopt the contingency measure analysis (for the 2008 and 2015 standards) and submit the SIP update to ARB for submittal to EPA. The Yolo-Solano Board adopted the analysis on October 9, 2024. |
| Disapproval of Plan; Contingency Measures | June 15, 2023 | EPA published a disapproval of the SFNA contingency measures (88 FR 39179). This disapproval started a sanctions clock, which will trigger increased offset ratios (January 17, 2025) and potential highway sanctions (July 17, 2025). |
| Finding of Failure to Submit | January 17, 2023 | EPA published a Finding of Failure to Submit (88 FR 2541) related to Section 185 Penalty Fee rule. The District adopted Section 185 rule on May 8, 2024 and it was submitted by ARB to EPA on July 1, 2024. On August 8, 2024 the EPA determined the submittal to be complete and stopped the sanctions clock. |
| California 2020 Milestone Compliance Demonstration (MCD) | March 30, 2021 | The ARB developed this report which showed how 9 areas in the state (including the SFNA) met the 2020 milestone requirements. |
| California Update to Plan | October 25, 2018 | In response to some court decisions the ARB Board adopted “2018 Updates to the California SIP” on October 25, 2018. The EPA approved all elements of the Plan, except for contingency measures, on October 21, 2021 (86 FR 58581). |
| NNSR Certification | March 14, 2018 | Our Board certified that our Non-attainment New Source Review (NNSR) program meets the requirements for the implementation of the 2008 ozone NAAQS and submitted it to EPA. EPA published a final rule on December 13, 2018 (83 FR 64026) approving the certification. |
| Sacramento Regional 2008 NAAQS Attainment and RFP Plan | October 11, 2017 | The District’s Board of Directors adopted the Sacramento Regional 2008 NAAQS 8-Hour Ozone Attainment and Reasonable Further Progress Plan (Plan). |
| RACT SIP | September 13, 2017 | The District’s Board of Directors adopted the RACT SIP on September 13, 2017. On July 3, 2018, EPA approved the negative declarations (83 FR 31072). On June 30, 2023 EPA proposed a limited approval/limited disapproval (88 FR 42252) and approved all elements except Non-CTG major sources of NOx On March 14, 2024 EPA approved (89 FR 18546) the major source NOx element, which was the last remaining element of the District’s RACT SIP. |
| Finding of Failure to Submit | February 3, 2017 | EPA published a Finding of Failure to submit (82 FR 9158) certain SIP elements for 15 states, including for our district the following elements: – Non-attainment NSR Rule – Non-CTG VOC RACT for major sources – NOx RACT for major sources – CTG VOC RACT (for all 44 CTGs) |
| Designation | May 21, 2012 | The Sacramento Metro area was designated “Severe” non-attainment for ozone (77 FR 30088) with an attainment date of no later than July 2025. |
1997 NAAQS; 8-hour standard of 0.08 ppm (84 ppb) (revoked)
| Document | Date | Description |
| 8-Hour Ozone Attainment and Reasonable Further Progress Plan | September 26, 2013 | In 2013 the regional air districts developed the Plan to demonstrate how the region would attain the 1997 8-hour standard. This plan was approved by U.S. EPA effective March 2, 2015 (80 FR 4795). |
| Sacramento Regional 8-Hour Ozone Milestone Report | October 25, 2012 | The region demonstrated how existing control strategies have provided the emission reductions needed to meet the federal Clean Air Act requirements for reasonable further progress toward attainment of the 1997 8-hour NAAQS. |
| Bump up | May 5, 2010 | The Sacramento Metro area was approved (75 FR 24409) for a bump up to “Severe” with an attainment date of June 2019. |
| RACT SIP analysis | September 13, 2006 | Adopted by the District’s Governing Board in September, 2006. The analysis was approved by EPA on April 6, 2018 (83 FR 14754). |
| Designation | April 30, 2004 | The Sacramento Metro area was designated “Serious” non-attainment for ozone (69 FR 23858) with an attainment date of no later than 1999. |
1979 NAAQS; 1-hour standard of 0.12 ppm (124 ppb) (revoked)
| Document | Date | Description |
| Re-designation Substitution Request | August 24, 2017 | The EPA determined that areas may demonstrate attainment with a revoked standard by submitting a Re-designation Substitution Request. The Sacramento region submitted the request, but no action taken by EPA (due to United States Court of Appeals Court decision). |
| Determination of Attainment of the 1-Hour Ozone National Ambient Air Quality Standards | October 18, 2012 | The EPA published a final rule that on October 18, 2012 (77 FR 64036) that the Sacramento Metro Area has attained the 1-hour ozone standard, and that excludes certain exceedances as caused by ozone exceptional events. |
| Supplemental report | June 26, 2012 | The districts submitted additional information supporting the April 26, 2010 attainment determination and Section 185 termination determination request. |
| Exceptional Event Demonstration | March 30, 2011 | This report shows how wildfires contributed to high 1 hour ozone concentrations in 2008. |
| Attainment determination | April 26, 2010 | The districts of the region submitted this report to provide supporting documentation to request a formal attainment determination for the 1-hour ozone NAAQS for the SFNA. |
| Bump up | April 25, 1995 | The Sacramento Metro area was approved (60 FR 20237) for a bump up to “Severe” with an attainment date of November 2005. |
| Attainment Plan | November 15, 1994 | The districts of the Sacramento region developed the attainment plan in November 1994, which showed how the region would attain the 1979 1-hour ozone NAAQS. |
| Designation | November 6, 1991 | The Sacramento Metro area was designated “Serious” non-attainment for ozone (56 FR 56694) with an attainment date of no later than 1999. |
State Ozone Plan
| Document | Date | Description |
| Triennial Plan | 2019 | The most recent plan covers the years 2015-2017. The document summarizes emission trends over this time period, forecasts future emissions, and reviews efforts made by the District to improve air quality. |
| Air Quality Attainment Plan | 1991 | The District originally adopted an Air Quality Attainment Plan (AQAP) in 1991 and has completed seven triennial plan updates since then. |
