## 4 Simulation Results and Discussion
### Reactive-Species Concentrations  
Figure 3 shows the computed vertical concentration profiles of the reactive species in the TKM from 10 through 200 min. Rapid convective transport in the model gives rise to nearly uniform vertical concentration profiles while continued surface emissions of RH ensure that its concentrations increase steadily with time. The temporal variations of NO concentrations are more complex, as will be discussed below. The large gradients for most species near the upper and lower boundaries are due to the physical processes of emission and entrainment fluxes, surface removal, and the rapid upward convection. Figure 4 shows the temporal behavior of the six reactive species and the two end-product species H\({}_{2}\)O\({}_{2}\) and HNO\({}_{3}\) for each of the surface, middle and top layers of the model. Here the complex early-time behavior of most of the species is clearly evident. The concentrations of the end products, H\({}_{2}\)O\({}_{2}\) and HNO\({}_{3}\), increase monotonically out to 200 min because, in this simulation, they are created but not lost from the CBL. Their concentrations at a given time can thus be used as indications of the cumulative amounts of chemical processing. Figure 3: Vertical distribution of concentrations for reactive species at 10, 20, 30, 60, 120, and 200 min. Simulation designed with emission fluxes for reactive species and no emission fluxes for other reactive species: (**a**) NO, (**b**) O\({}_{3}\), (**c**) NO\({}_{2}\), (**d**) RH, (**e**) HO\({}_{2}\), and (**f**) OH at the surface layer and with flux exchanges between CBL and FA for all reactive species. Figure 2: Vertical distribution of concentrations for inert species at 10, 20, 30, 60, 120, and 200 min. Simulation designed with emission fluxes for inert species NO and RH and no emission fluxes for inert species O\({}_{3}\) and NO\({}_{2}\) at the surface layer and with flux exchanges between CBL and FA for all inert species. During the first 20 min of model time, the chemical development proceeds as the emitted NO quickly starts to fill the CBL; its concentrations rise in all layers while photolysis of NO\({}_{2}\) serves to increase both NO and O\({}_{3}\) concentrations. The increase in O\({}_{3}\) concentrations leads to an increase in OH concentrations. This and the increasing RH concentrations lead to increasing HO\({}_{2}\) concentrations except in the top layer. There, the increasing NO concentrations and decreasing RH concentrations result in initially decreasing HO\({}_{2}\) concentrations via R\({}_{5}\) and R\({}_{6}\). At about 10 min, the HO\({}_{2}\) concentrations begin to increase slightly and to reach a local maximum at about 15 min. Since the HO\({}_{2}\) concentration is computed from the PSSAc, the behavior of HO\({}_{2}\) in all layers can be rationalized by examining the temporal variations of the four non-radical reactive species in Figure 4 and referring to Table 1. The same is true for the OH behavior in time. Entrainment of air from the free troposphere causes the decreasing O\({}_{3}\) and RH concentrations in the top layer. Note that the concentration differences in the middle layer over the interval of 0-20 min are about equal but opposite for NO and NO\({}_{2}\). After 20 min, the NO concentrations decrease in all layers because of reaction with O\({}_{3}\); thus resulting in increases in NO\({}_{2}\) concentrations after the latter reach minima at 20 min. Concurrently, O\({}_{3}\) concentrations start to decrease at similar rates in all layers. The NO concentrations reach minima in all layers at times varying from about 40 min for the top layer to about 70 min for the surface layer. A comparison of NO and NO\({}_{2}\) concentration differences over appropriate intervals reveals that the stoichiometric changes for NO\({}_{2}\) are a little larger than for NO. For example, in the middle layer, the NO concentration decreases by about 0.05 ppb in the interval of 20-70 min, while the NO\({}_{2}\) concentration increases by about 0.07 ppb.