Continuous Measurements of Ozone and Nitrogen Dioxide at Two Heights in Houston, TX

The Houston-Galveston-Brazoria area (HGB) is in non-attainment for O3 with approximately 47 days above the current 8-hour standard of 75 ppbv in 2011. Based on data collected from 2008-current, we find that O3 at the roof of the Moody Tower on the University of Houston (UH) main campus is typically ~10% higher than all surrounding ground level sites when comparing the 1pm data. During the fall of 2011 and summer of 2012 the TCEQ sponsored UH to collect measurements of O3, CO, NO, and NO2 at a ground-level site (6m AGL, first layer in regional photochemical models) within ½ mile of the existing Moody Tower roof-top site (70m AGL, second layer in regional photochemical models) to investigate the reasons for the higher values aloft. Additional measurements of NO and NO2 were added to the existing O3 and CO measurements at the Moody Tower as well. All measurements were cross-calibrated to ensure comparability. The results presented will examine the relative importance of several factors that contribute to the observed differences, and will highlight the need to measure both NO2 and O3 to get a more complete picture, and the benefits of measuring O3 and NO2 at elevated sites in order to constrain the regional photochemical models in at least 2 layers.