6.3
The effect of vertical diffusivity on photochemical model estimates of tropospheric ozone
Robert E. Imhoff, Tennessee Valley Authority, Muscle Shoals, AL; and E. M. Bailey and S. F. Mueller
Vertical diffusivity (Kv) is used to parameterize the subgrid scale vertical mixing in three-dimensional photochemical models. These models are commonly used for regional-scale analyses of ozone formation, transport and fate. Kv is not directly output by the meteorological models used to generate input to the photochemical models, but must be diagnosed by differing methods. The issue of the effect of Kv on photochemical models has not been extensively investigated. This paper discusses the effect of alternative Kvs on photochemical model performance and the practical implications for interpretation of modeling results from regional and local ozone modeling studies.
The UAM-V version 1.24 model was applied to the urban areas of Nashville and Memphis, Tennessee, and to a large NOx point source in middle Tennessee. High and low values of Kv were used in 4 km grid resolution model runs. The model output for Nashville is compared for two days where in situ airborne measurements were available from a helicopter that was flying in a grid-like pattern to characterize the concentration fields. Additional comparisons were made for the point source plume between model and measurements by the helicopter.
Variation of Kv was found to significantly affect the NOy and O3 concentration fields, sometimes in unexpected fashion. For example, the point source plume as actually modeled to mature faster with lower vertical diffusivity.
Session 6, Photochemical air quality models
Tuesday, 11 January 2000, 8:30 AM-10:00 AM
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