## 4 Simulation Results and Discussion
### Comparisons with Other Models
The results for the NO\({}_{\rm x}\)-O\({}_{3}\)-RH system are the same as previously discussed, but are presented here from a different perspective. The striking feature is that the trajectories for the CKM have distinctly different shapes and tendencies from those of the TKM in all layers. This is yet another way of portraying the segregation effects on the NO-O\({}_{3}\) reaction pair. They act to separate the ranges of variability of NO concentrations and to produce slightly overlapping ranges of O\({}_{3}\) concentrations. By contrast with those for the NO\({}_{\rm x}\)-O\({}_{3}\)-RH system, the TKM and CKM trajectories for the NO\({}_{\rm x}\)-O\({}_{3}\) system, while showing early differences, are quite similar in all layers for later times. In the top layer they become parallel, separated by about 0.2 ppb NO at any time after about 20 min. The tendencies for parallel behavior are evident in the bottom and middle layers, but they approach it at later times. From the foregoing and Figure 7, it is evident that in the TKM the effect of RH sources when added to the NO sources is to restrict the range of variability of NO and O\({}_{3}\) concentrations. Finally, we compare the TKM with the LES simulation [25] of the same chemical mechanism. The fundamental differences in the two approaches lie in their dimensionality (three vs. one), atmospheric dynamics, sub-grid scale parameterization, and initial times and conditions for simulation. These differences impede detailed comparisons. However, the relatively uniform vertical distributions of species and segregation coefficients and the time evolution of intensity of segregation for R\({}_{3}\) have significant similarities. The LES results for uniform source distribution provide generally significantly lower segregation intensities than the TKM. The TKM produced similarly low values in the sensitivity analysis when the molecular time scale was increased. Since the Damkohler number is the appropriate scaling parameter for comparing intensities of segregation, decreasing the turbulent time scale (\(\tau_{t}\)) in the TKM would also produce similarity. However, the value of \(\tau_{t}\) of 11 min was chosen in the TKM to be the same as in the LES. It is difficult to point to any single quantity that may account for the differences, but it seems quite probable it lies in the parameterizations that exist in both models rather than in a fundamental difference in the physical and chemical processes represented in them. There remains the difficult task of performing adequately time-resolved concentration measurements of reacting species in the turbulent convective boundary layer to determine if and to what extent turbulent segregation occurs. The sensitivity analysis reveals the following:  
* The concentrations of OH and HO2 varied the most (relative to the reference case concentrations) of any other species modeled in the TKM. This is because the mechanism for the oxidation of RH and cycling of NOx involves chain reactions with the HOx radicals as the principal intermediates at very low concentrations between the much more abundant emitted species and their end products. * The concentrations of NOx, HOx and RH modeled in the TKM were most sensitive to changes in the emission rates of NO and RH. * Because the initial concentrations of O3 are much larger than for the other species, they varied on an absolute basis more than any species except RH. However, because the reaction scheme is cyclical for O3, it varied little relative to the reference case. * The segregation effects of turbulence on R5 and R6 were promoted by increased emission rates of RH and NO, respectively. Decreased emission rates of those species diminished the effects of turbulence.