Masters Theses

Nianjun Zhou

Date of Award

5-1992

Degree Type

Thesis

Degree Name

Master of Science

Major

Environmental Engineering

Major Professor

Wayne T. Davis

Committee Members

Terry Miller

Abstract

This thesis discusses the methods for simulation of ozone formation in the middle Tennessee area for the summer time of the base year of 1988. Two photochemical models developed by Systems Applications Incorporated were used for the modeling purposes. They were the OZIPM-4 model and the Urban AIRSHED model. As a photochemical trajectory model, the OZIPM-4 model was used first to find the ozone profiles at Hendersonville, TN where a monitoring station is located. The inputs of the model included the hourly emissions (kg/sq-km) of volatile organic compounds and nitrogen oxides by chemical species, the meteorological conditions, the aloft ozone concentration and initial air quality conditions. The meteorological conditions used in the simulations (wind velocity, temperature and relative humidity) were determined by analyzing the ten highest days of ozone concentrations in the middle Tennessee area for 1986, 1987, and 1988. The trajectories of air parcels passing over the Hendersonville air monitoring site were determined based on the chosen wind field for the ozone formation. Obviously, different air parcels arrived at Hendersonville at different times. The simulations of ozone formation of those air parcels allowed the development of the ozone concentration profile verse time for the Hendersonville site. The air parcel was initiated at 6:00 AM with the chosen initial conditions and picked up the hourly emissions of pollutants as it moved toward the Hendersonville site. The approach was basically one of finding a solution in an Eulerian Coordinate System by solving it in a Lagrangian Coordinate System. The research indicated that ozone formation was sensitive to wind field, mixing height, initial conditions, anthropogenic emissions, biogenic emissions and aloft ozone concentration. The results showed that the largest single contribution to ozone formation was from mobile sources. Finally the Urban AIRSHED model, a numerical grid model, was used to simulate the physical and chemical processes of ozone formation using a 20 x 20 x 3 grid system with 5 km x 5 km horizontal resolution. Vertically, the region was divided into three layers, two layers below the mixing height and one layer above it. The model showed that the ozone peak formed in the later afternoon near Hendersonville if wind direction was from southwest to northeast. It was interesting that an ozone hole was found from the output results, which was located at a large nitrogen oxides source. The discovered ozone hole illustrated the scavenging effects of nitrogen oxides. The results obtained from the two models were compared. A discussion of the advantages and disadvantages of the two models was included after detailed analyses of the simulation processes and the outputs of the two models.

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