Tropospheric ozone is a secondary pollutant formed by a reaction of volatile organic compounds (VOC's) and nitrogen oxides (NOx) in the presence of sunlight. Inhalation of tropospheric ozone can trigger a variety of health ailments, including chest pain, throat irritation and congestion, along with creating an increased risk of bronchitis, emphysema and asthma. In 2001, the EPA implemented the Nitrogen Oxides State Implementation Plan Call (NOx SIP Call) in an effort to mitigate the formation of tropospheric ozone concentrations by reducing NOx emissions which contribute to ozone formation. However, tropospheric ozone formation is also effected by variations in meteorological factors and biogenic emissions. The main goal of this project was to use hourly data to develop an autoregressive linear model to account for the meteorological and seasonal impact on ozone. The data analyzed included hourly ozone and meteorological data from the Clean Air Status and Trends Network (CASTNET) for May through September from 1997 to 2006. The four sites analyzed included Beaufort, Candor, Coweeta and Cranberry, North Carolina.

Another goal of this project was to examine local sources of tropospheric ozone and its precursors using several different exploratory methods. Such methods used in this study included Finger plots, Bull's Eye plots, and localized back trajectories. Finger plots focus specifically on the determination of local sources of ozone concentration, while the Bull's Eye plots focus on the temporal variation of ozone concentration at a given site. Finger plots and Bull's Eye plots were created for all of the 4 CASTNET sites above and also for two pairs of collocated North Carolina Environment and Climate Observing Network (NC ECONET) and North Carolina Division of Air Quality (NCDAQ) stations in western North Carolina. Localized back trajectories focus on tracing air parcels back through time and space over only a few hours, where other back trajectory approaches such as the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) Model go back 12 hours or more. Results of both parts of this project will be presented.