Ozone International Transport Demonstrations
Federal Clean Air Act (FCAA), §179B(b) allows states to develop and submit to the U.S. Environmental Protection Agency (EPA) a demonstration that a nonattainment area would have attained a National Ambient Air Quality Standard (NAAQS) “but for” emissions emanating from outside the U.S. This page provides details and documents related to the §179B(b) demonstrations that TCEQ submitted to EPA for the 2008 and 2015 eight-hour ozone NAAQS.
TCEQ created demonstrations showing that nonattainment areas in Texas would have attained the 2008 and 2015 eight-hour ozone NAAQS “but for” emissions emanating from outside the U.S. The demonstrations use modeling analysis, atypical day analysis, previously submitted exceptional event demonstrations, and other weight of evidence, as needed, to show that monitors in Texas’ ozone nonattainment areas would have attained the 2008 and 2015 ozone standards “but for” emissions emanating from outside the U.S.
The demonstrations were sent to EPA for approval on July 2, 2026, and are accessible below:
- Demonstration Summary (English)
- Demonstration Summary (Spanish)
- 179B(b) demonstration for Dallas-Fort Worth (DFW) 2008 eight-hour ozone nonattainment area (English only)
- 179B(b) demonstration for Houston-Galveston-Brazoria (HGB) 2008 eight-hour ozone nonattainment area (English only)
- 179B(b) demonstration for Bexar County 2015 eight-hour ozone nonattainment area (English only)
- 179B(b) demonstration for DFW 2015 eight-hour ozone nonattainment area (English only)
- 179B(b) demonstration for HGB 2015 eight-hour ozone nonattainment area (English only)
Associated Appendices and Attachments:
- Appendix A – Modeling Technical Support Document (English only)
- Appendix B - Atypical Events Technical Support Document (English only)
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- Attachment 1: Weather and Satellite Maps
- Attachment 2: Backward Trajectories by Monitor for each Atypical Event Day
- Attachment 3: TCEQ Forecast Discussions
- Attachment 4: Fire/Smoke Maps and Satellite Aerosol Products Combined with Backward Trajectories for Days Prior to Atypical Event Days
- Attachment 5: Emission Events Reported Around Atypical Event Days
Modeling Files
- Details and access to modeling files related to the above demonstrations.
Related Topics
- TCEQ Index of Air Topics lists a wide range of programs and how the agency is working to improve air quality in Texas.
- TCEQ Exceptional Event Demonstrations for Ozone events.