The goal of this work was to improve the quality and confidence level of the Baylor University Twin Otter data set that was submitted as part of the TexAQS 2000 air quality study and to prepare a self-consistent data set for the flights conducted during TexAQS 2000 for subsequent data analysis. The work focused on the data collected for NO, NO₂, NO_y, NO_y* (NO_y – HNO₃), ozone, CO, and SO₂. Data quality was improved by identifying an appropriate averaging interval for the data. The confidence level of the data was established through creation of an uncertainty budget for the measurements. Also presented are the results of measurement intercomparisons conducted with other aircraft and surface platforms, and a ground-based standards comparison