## 4 Simulation Results and Discussion
### Comparisons with Other Models  
Comparing the TKM to three other models further shows the effects of turbulence on the photochemical system in the CBL. The models and their characteristics are listed in Table 3. In order of complexity, these are a chemistry-only box model (BMCh), a box model (BM) and a chemical kinetics model (CKM). The results of the simulations for the middle layer of the CBL are shown in Figure 6. Since the box models have no dimensionality, the results shown in Figure 6 are merely the single sets of concentrations computed in the models. The initial concentrations of species are those of [PERSON] et al. [25], and these were used in each simulation. The BM maintains a balance of physical and chemical processes, considering the whole CBL as a box. The physical processes simulated are emission, deposition and exchange between CBL and free atmosphere. The chemical processes are the full set of reactions given in Table 1. Since there is no turbulence and only one compartment of the CBL, the chemical kinetics terms contain only the mean concentrations. The BMCh represents only photochemistry with no emissions of NO and RH. There are no physical processes, viz. emission, deposition, exchange, transport, and turbulence. As the photochemical reactions proceed, concentrations of NO and NO\({}_{2}\) decrease toward zero. The CKM has all of the features of the TKM except \(I_{s}=0\). Thus, it represents the usual approach to transport and chemistry using only average concentrations of species in the reaction rate expression. Except for O\({}_{3}\), the results of the BM and CKM are very similar to each other for all species over the 200- min time period. For these models, the concentrations of all reacting species remain nearly constant over 200 min, except for O\({}_{3}\). Their slight decrease in time is caused by dry deposition. Figure 6: Temporal behaviors of reactive species concentrations in the middle layer. Data are from the models BMch, BM, CKM, and TKM. The TKM results shown in Figure 6 are the same as those for the middle layer shown in Figure 4. The differences between the CKM and the TKM are attributable to the retarding effects of turbulence on the important reaction rates, because in the CKM, \(I_{s}\) = 0. Thus, the large early segregation between NO and O\({}_{3}\) (see Figure 5b) combined with photolysis causes the NO\({}_{2}\) concentrations to decrease and keep NO concentrations higher than for the CKM. The early photolysis of NO\({}_{2}\) contributes to the increase in O\({}_{3}\) and OH concentrations and thus, retards the rise of \(RH\) concentrations. However, NO-O\({}_{3}\) segregation, combined with the continued emissions of \(RH\) along with 50 % segregation between RH and OH, ultimately chokes off the HO\({}_{\rm x}\) and NO\({}_{\rm x}\) cycling reactions. This prevents the O\({}_{3}\) concentrations from increasing as they would in the CKM. Thus, the choking-off effect leaves the NO and NO\({}_{2}\) concentrations higher than in the CKM while the O\({}_{3}\) concentrations are lower. All of this is reflected also in the lower rates of buildup in the TKM of H\({}_{2}\)O\({}_{2}\) and HNO\({}_{3}\) cumulative concentrations. Another set of model simulations was carried out to compare the TKM with the CKM for the reversible NO\({}_{\rm x}\)-O\({}_{3}\) system [10]. In the analysis below, we also compare the results with those obtained for the NO\({}_{\rm x}\)-O\({}_{3}\)-RH system. All simulation conditions in the models are the same except for the chemical mechanisms. As in the previously discussed TKM and CKM simulations, initial concentrations are 68.8 ppbv of O\({}_{3}\) and 0.138 ppbv of NO. Figure 7 shows the results in the form of NO-O\({}_{3}\) time trajectories for the bottom, middle and top layers of the CBL. Clearly the NO\({}_{\rm x}\)-O\({}_{3}\)-RH chemical mechanism (triangle) shows markedly different behavior from the simple NO\({}_{\rm x}\)-O\({}_{3}\) case (diamond).