Tropospheric Ozone: Health Effects, Control Strategies, Process Analysis and Source Apportionment

Ozone (O3) is a reactive oxidant gas, produced naturally in trace amounts in the atmosphere. A large amount of O3 is found in the stratosphere where it plays a critical role in absorbing UV radiation emitted by the sun. While stratospheric O3 shields us from UV, ozone at ground level can cause adverse effects to both human health and the environment. The need to protect health and the environment led to the national air quality standards for ozone. Since the 15th of June 2005, the 8-hour average National Ambient Air Quality Standard (NAAQS) for ozone is 0.08 ppm. To keep the concentration of O3 below the standard, control strategies for the reduction of O3 precursors are required. The design of these strategies relies on regional photochemical models to predict the possible success before implementation. It is also useful to quantify the percentage that each O3 precursor, NOx and VOC, has contributed to these concentrations. This report concentrates on simulations of the Houston area, for the period 08.22-09.06.2000. The model used for the study is CAMx. The pyPA tool (Process Analysis in python) was used for the post-process analyses of the model outputs to quantify the chemical and physical processes that led to ozone formation. For this period, runs were conducted with several different emission inventories, all showing lower concentrations than measured. Evaluation of model performance led to the hypothesis that a lack of OH radical sources could be a reason for poor predictions. Several sensitivity simulations were examined to measure the impact of higher levels of OH on ozone. These scenarios included increases of direct sources of OH radicals, internal sources of OH radicals, and an increase of carbon monoxide. The increase of direct sources of OH radicals led to the highest O3 concentrations.Master of Science in Public Healt