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Recently there have been discussions about the DFW SIP Model performance. In order to correct the errors in the model some suggested that new modeling episodes would have to be developed, which takes a considerable amount of time, and would likely prohibit TCEQ from meeting the SIP deadlines. After some review TCEQ has indicated that they believe they can make improvements to the model and will be able to submit the SIP without changing the model episode.
There are also challenges to the Houston/Galveston/Brazoria area air quality model. Although the model meets the EPA's quality assurance criteria, some research suggests that significant changes must be made to improve the model accuracy and identify the proper control strategies. There are no plans to change the model episode, however new data is continually being incorporated into the model to improve performance.
Both the Houston/Galveston and Dallas/Fort Worth areas have been designated by the EPA as "moderate" in terms of their 8 hour ozone violation standard, which means they must be in compliance with the 8-hour ozone standard by June 2010. Both areas have the option to request EPA for a reclassification to a designation of "severe", which would delay the required compliance date until June 2013. As of this writing neither area has requested a reclassification.
Introduction
According to the Clean Air Act (CAA), the EPA requires all states to submit a State Implementation Plan (SIP) to address all areas that do not comply with the National Ambient Air Quality Standards (NAAQS). A SIP contains the set of actions or control measures that the state plans to implement to meet the NAAQS. In order to demonstrate that the control measures will bring about attainment a model must be generated. The model is given the information available from the area in question such as the emissions inventory, the meteorology, etc. The model results must match the pollutant levels experienced during the test episode within quality assurance standards set by the EPA. If the model demonstrates that it can accurately describe the past, then the emissions inventories are reduced until the model demonstrates that the area will meet the NAAQS requirements by the specified date.
More information about SIP's in Texas can be found at the following websites:
State Implementation Plan (SIP) Timelines
There are many steps involved in developing a SIP and submitting it to the EPA. For the 8-hour ozone SIP the deadline for submission is exactly 3 years after the EPA designations were published, or June 15, 2007. Below is an example of a typical SIP timeline that may apply to both the Houston/Galveston/Brazoria area and the Dallas/Fort Worth area; however the dates prior to the June 15, 2007 are set by the state and can change significantly. Also, the state may decide to apply for an extension of the SIP compliance date from 2010 to 2013, which will change all of the dates below.
| Control Strategy Catalog Completed | August 2005 |
| Final Base case Development of 2000 Episode | September 2005 |
| Future Case Modeling 2000 Episode | October 2005 |
| Control Strategy Modeling | December 2005 - February 2006 |
| Rule Proposals | August 2006 |
| Public Comment | October - November 2006 |
| TCEQ Review/Response/Revisions | January 2007 |
| SIP Adoption by TCEQ commissioners | March 2007 |
| Submit to EPA | June 15, 2007 |
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| Page Updated/Reviewed: 02/15/2007 10:32 AM |
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© 2005 - 2008 Texas Environmental Research Consortium
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