The estimation of mixing height and its effects on the urban airshed model's prediction of tropospheric ozone concentration

Ouattara Fatogoma, Purdue University

Abstract

Mixing height strongly influences the Urban Airshed Model's (UAM-IV) prediction of tropospheric ozone concentration. Thus, in this thesis, a mixing height estimation model is developed based on theoretical parameterization equations of surface sensible heat and momentum fluxes in the lower atmosphere. The model uses only available routine meteorological and terrain characteristics data. The evaluation of the performance of the proposed mixing height estimation model against the observed hourly mixing heights obtained from the Lake Michigan Ozone Study field experiment of July 15-19, 1991 shows that the predictions match the observations very well. The average geometric mean of the predicted to observed hourly mixing height ratios is equal to 0.99. The outputs of the proposed hourly mixing height model along with those of the hourly mixing height model incorporated in the UAM-IV package are used in the UAM-IV to simulate hourly average tropospheric ozone concentration in the Indianapolis metropolitan statistical area during the ozone episode of June 25-28, 1990. The modeling domain is 112 Km by 112 Km wide and divided into a horizontal array of 4 Km by 4 Km grid cells and five vertical layers. A comparative study performed to assess the effects of mixing height on the prediction of tropospheric ozone concentration by the UAM-IV shows that the UAM-IV performs better in predicting hourly average ozone concentration when the mixing height fields are from the proposed mixing height estimation model. For example, the episodic mean of the unpaired highest prediction accuracy, the average station absolute peak prediction accuracy, the average normalized bias, the average normalized absolute bias, the correlation coefficient, and the fractional bias of the mean are 10.6%, 8.3%, 1.2%, 18.6%, 0.71, and 0.01, respectively when the mixing height fields are from the proposed hourly mixing height model. They are 20.2%, 9.5%, 6.6%, 20.1%, 0.66, and $-$0.05, respectively when the mixing height fields are from the UAM-IV hourly mixing height model. Moreover, the spatial coverage of the predicted one-hour average ozone concentration daily peaks shows that hourly ozone concentrations are the highest in the northeastern quadrant of the study domain downstream of the source area (Indianapolis).

Degree

Ph.D.

Advisors

Jacko, Purdue University.

Subject Area

Civil engineering|Atmosphere|Environmental science

COinS