Climate Change Impacts on Regional and Urban Air Quality in South Texas

Temperature changes are precursors to climate variability in a region. Climate change is emerging as an important ingredient of air quality and the link between the two issues will have a significant impact on air quality in the future. The recent Intergovernmental Panel on Climate Change (IPCC) report predicts significant temperature increases over the century. This modeling study presents results from a preliminary investigation, undertaken for a high ozone episode of September 16 to 19, 1999 that affected the South Texas region. The study determines the impact of such temperature perturbations on tropospheric ozone concentrations in this region. These temperature perturbations represented the worst case consequences of extreme climate change within the study region. Significantly large changes in peak ozone concentrations were predicted. Temperatures also had an appreciable spatial impact on the number and extent of eight-hour ozone exceedances with an average of 34% increase in area exceeding the National Ambient Air Quality standards for ozone in the study region for successive increase in temperature. In addition, transboundary flux from major industrialized urban areas also played a major role in supplementing the high ozone concentrations during the perturbed temperature scenarios. It is well known that nighttime temperatures have increased at almost twice the rate of daytime temperatures in context of climate change due to increased evaporative cooling during the daytime hours. A sensitivity run was conducted which dealt with the relative influence of daytime versus nighttime increases of temperatures on daily peak ozone concentrations. The nighttime perturbations of ambient temperatures resulted in a disproportionate increase of the daily maximum eight-hour averaged ozone concentration.