Due to the sparseness of routine concentration profile measurements, the evaluation of photochemical model concentrations in layers aloft has been rather limited. In-situ observations obtained by instrumented aircraft flights during intensive field studies have been valuable and are relied upon in efforts to investigate a model's ability to simulate species concentrations in the daytime planetary boundary layer (PBL). In this study, observed concentrations collected aloft by research aircraft during the Second Texas Air Quality Study (TexAQS II) are used to investigate the ability of the Community Multiscale Air Quality (CMAQv4.71) model to reproduce the distribution of ozone and other pollutant species within and above the afternoon PBL. Model simulations with CMAQ using meteorological fields generated by the Weather Research and Forecasting (WRF) model using four-dimensional data assimilation (FDDA) were performed on a domain encompassing the greater Houston, TX region with a 4-km grid cell size and 34 vertical layers. The modeling period spanned the entire experimental study period of August 1 through October 15, 2006.

Emphasis in this model evaluation is on the high resolution (in the horizontal and vertical) ozone measurements obtained by a downward-looking lidar system on-board the NOAA Twin Otter aircraft during flights conducted on selected afternoons in the Houston metropolitan area. Comparisons of modeled ozone concentrations will be made to assess how well the horizontal distribution and vertical structure of modeled ozone compare to the observed ozone patterns across the urban plume at various distances downwind. In addition, CMAQ model results using refined meteorological fields generated from WRF simulations that incorporated supplemental wind profiler measurements into the FDDA procedure will also be evaluated against the observed vertical ozone cross-sections to determine if these modeled ozone patterns more accurately reflect the spatial ozone pattern than the base case results. Selected species profile measurements obtained during flights of the NOAA WP-3 research aircraft in the Houston area from different case study days will also be compared against the modeled concentration profiles from CMAQ simulations driven by the different meteorological data sets to discern the impact of the refined wind fields on modeled concentrations.