Investigating the Impacts of Meteorology and Long-Range Transport on near Surface and Free Tropospheric Ozone over Texas

Ozone produced photochemically in the atmosphere is important from a regulatory and health standpoint. Efficient control technologies and strategies for ozone precursors over the past 20 years have had a noticeable effect on ozone concentrations in many cities across Texas. Although ozone exceedances over the National Ambient Air Quality (NAAQS) standard for ozone have decreased over time, they still exhibit year-to-year variability, likely due in part to changes in meteorological patterns. This dissertation will study the impact of meteorological patterns and sources of ozone precursors on ozone variability at the surface and in the upper levels of the atmosphere. Through the use of multiple ozonesonde and model-simulated profiles, a case study of a significant enhancement of free tropospheric ozone is analyzed. The source of the enhancement was determined to be direct production of ozone from corona discharges; calculated enhancement values agreed with previous studies. The second topic of my thesis focused on understanding long-term trends in ozone and meteorological patterns over Dallas Fort Worth metropolitan area. In order to do this, I utilized surface ozone observations from the Texas Commission for Environment Quality (TCEQ)’s CAMS and the United States Environmental Protection Agency (USEPA)’s AQS networks, gridded meteorological data from the North American Regional Reanalysis (NARR) dataset, and model simulations using the USEPA’s Community Multiscale Air Quality (CMAQ) model to characterize wind patterns associated with different ozone regimes. The model results indicated downwind pollution impacts from Houston on DFW ozone underscoring the impact of specific wind patterns on air quality in DFW. In my third and final chapter, I quantified the impact of biomass burning on ozone photochemistry was quantified. Through comparison of model sensitivity simulations, it was concluded that biomass-burning products transported to Texas made the boundary layer and free troposphere more NOx sensitive hence influencing photochemistry during the time period of interest. The findings of this study result in a better understanding of sources and variability of near-surface and free tropospheric ozone.