In April 2025, revisions to Regulation 3 were published to the Colorado Register establishing new regulatory requirements for annual toxic air contaminant (TAC) reporting. These requirements will be fully implemented beginning with the 2026 TAC emissions report, due June 30, 2027, and represent significant changes to the TAC reporting program as it is currently established. However, recent guidance published by the Division indicates that facilities may use certain streamlining opportunities (i.e., exemptions and reporting thresholds) from the Regulation 3 changes for their 2025 calendar year TAC emissions report.
Facilities subject to TAC reporting should familiarize themselves with these updates to ensure that equipment operation and emissions are tracked in accordance with the revised requirements. Although these reports are not due until June 30, 2027, it is important for facilities to ensure that data being collected during 2026 will allow for accurate reporting submitted in 2027.
The Division has also indicated that inspectors are on the lookout for facilities that did not submit required reporting for RY2023 or RY2024, and notes that facilities that missed submitting either or both of these reports should submit them as soon as possible.
Who is Subject
The new Regulation 3 requirements expand the list of facilities that are subject to annual TAC reporting. Currently, only synthetic minor and Title V major source facilities are required to submit an annual TAC report. Minor source facilities that meet the following criteria will be required to submit an annual TAC report starting in reporting year (RY) 2026:
- Facilities reporting any stack/fugitive air releases to the EPA Toxic Release Inventory (TRI), if releases of a TRI pollutant that is also a TAC are above de minimis thresholds in Appendix C of Regulation 3, Part A;
- Facilities reporting under Regulation Number 7, Part B, Section V;
- Facilities that use or emit ethylene oxide above the de minimis threshold in Appendix C of Regulation 3, Part A (3.20E-02 lb/year);
- Facilities that use and emit cadmium, nickel, or hexavalent chromium above the de minimis thresholds in Appendix C of Regulation 3, Part A (8.80E-02, 0.16, and 1.30E-02 lb/year, respectively) and whose activities include: electroplating, plating, polishing, anodizing, and coloring, or other industrial processes, including, but not limited to, thermal spraying, welding, plasma cutting, and metal heat treating or other metal fabrication, except for fuel combustion.
The revised Regulation 3 clarifies that unless otherwise arranged, in situations where there is a change of ownership or control of the facility, the owner or operator as of the reporting deadline (June 30) is responsible for submitting the annual emissions report.
For more details: Colorado Regulation Number 3, Part A, Section IX.A.1
Reporting Requirements and Thresholds
The RY2026 TAC report will look different from previous years’ reports. Facilities will no longer be allowed to report one facility-wide emission total for each TAC and instead will be required to report emissions on the individual emission point level. However, reports can group similar equipment under a single emission point or by equipment/activity type (fugitive, boilers, engines, etc.). Other key changes to the report will include:
TAC Pollutant List: The TAC pollutant list adopted into Regulation 3, Part A, Appendix C includes only 344 pollutants, a decrease from the 477 pollutants in previous years. Two new pollutants were added to Appendix C (black carbon and ultra-fine particles); however, these are exempt from reporting.
De Minimis Limits: Annual emission reports must include all TAC emissions at or above the de minimis reporting threshold limits in Regulation 3, Part A, Appendix C. The reporting threshold is based on the facility-wide annual actual TAC emissions for each individual TAC, inclusive of emission controls. The facility-wide total should only include equipment/activities owned or operated by the same reporting customer number. Any emissions from exempt activities in Regulation 3, Part A, Section IX.A.2 or Regulation 7, Part B, Section V.B.1.h.(iii) do not need to be included.
Criteria Pollutant Reporting: Actual emissions of criteria pollutants or precursors must be reported in the annual emissions report if uncontrolled emissions from an individual emissions point are above the APEN thresholds. Additionally, VOC or PM10/PM2.5 emissions must be reported if they are used in the calculations for reporting VOC- or PM10/PM2.5-affiliated TACs.
Exempted Sources: New exemptions to certain equipment and activities will apply to the RY2026 report (Regulation 3, Part A, Section IX.A.2.b), and guidance indicates that these exemptions can be applied to the RY2025 report. Facilities should verify that they are tracking emissions for all of equipment that will be subject to TAC reporting.
To simplify the exemption list, the Division has created a webpage to categorize these exemptions by source type. These exemptions only apply to sources that do not report through Oil and Natural Gas Annual Emission Inventory Reporting (ONGAEIR). For ONGAEIR sources, exempted equipment and activities are consistent with other exemptions in Regulation 7, Part B, Section V.C, though note that non-road engines are required for ONGAEIR criteria pollutant emission reporting, but not for TAC, consistent with the exemptions published in Regulation 3.
Revising a Report for Substantive Errors: The revised regulation contains provisions for revising a submitted report if the owner/operator or Division discovers that an annual report submitted within the previous two years contained one or more substantive errors. The deadline for submitting the revised report is either August 31 (if the substantive error is discovered between January 1 and June 30) or February 28 (if the substantive error is discovered between July 1 and December 31).
A refinement or improvement to an emissions estimate technique or emission factor is not considered a substantive error but should be noted in the report submitted following the refinement or improvement. Note this requirement is in line with the Regulation 7 requirement for revised ONGAEIR submittals.
RY2025 TAC Reporting Guidance
In February 2026, the Division released updated reporting guidance for the RY2025 TAC emissions report (due June 30, 2026). These updates were made to incorporate some of the reporting requirements adopted in Regulations 3 and 7 to help streamline the reporting process prior to these requirements becoming effective.
No new facilities will be subject to TAC reporting for RY2025; the TAC reporting requirement will continue to apply to Title V major and synthetic minor source facilities only. The RY2025 TAC report will incorporate the Regulation 3, Appendix C TAC pollutant list and the associated de minimis thresholds. The report should only include TAC pollutants with facility-wide emissions over the de minimis thresholds. The report will also incorporate the data source hierarchy. Exemptions in Regulation 3, Part A, Section IX.A.2 and Regulation 7, Part B, Section V can be applied for the RY2025 TAC reports.
An online information session is scheduled for February 18 at 11:00 AM to go over updates to the RY2025 reporting for sources that do not submit through ONGAEIR.
Recent and Upcoming Air Toxics Rulemaking
House Bill 22-1244, signed into law in June 2022, established requirements to develop an air toxics program with 5 key components. In addition to the TAC reporting program updates described above, the Division has undertaken and will continue to carry out the following actions pursuant to HB22-1244:
Air toxic monitoring program: In July 2025, the four new Phase 2 air toxics monitoring sites began operation in Pueblo, Colorado Springs, Canon City, and Wheat Ridge. The monitoring data from 2024 for the three Phase 1 sites in Commerce City, La Salle, and Grand Junction are now available to view.
Air toxic permitting needs assessment: The Division released the Colorado Priority Toxic Air Contaminant (PTAC) Permitting Program Needs Assessment in September 2025 which proposed a potential air toxics permitting program framework. If approved by the General Assembly, this report could be used to inform the development of an air toxics permitting program for priority TACs. The final report was submitted to the Colorado General Assembly December 31, 2025.
Health-based standards for PTAC: In October 2025, The Air Quality Control Commission (AQCC) adopted revisions to Regulation 30 to establish health-protective benchmarks for priority toxic air contaminants (PTAC). These benchmarks represent levels of pollutant concentrations below which adverse health effects are not expected to occur and include benchmarks for both cancer and non-cancer risk.
Emission control regulations for PTAC: In April 2026, The AQCC will hold a rulemaking hearing to consider proposed updates to Regulations 24, 26, & 30 to incorporate emission control regulations for new and existing sources of PTAC.
For support with your upcoming reporting requirements or questions on regulatory changes in Colorado, reach out to Kendall Maffet with the Trinity’s Colorado office.
