## 4 Simulation Results and Discussion
### Reactant Segregation  
When the chemical reaction timescale is of similar magnitude to or smaller than the turbulence timescale (\(\tau_{ch}\leq\tau_{t}\)), segregation of reactants becomes significant (\(I_{s}>0\) or \(I_{s}<0\)); thus, the reaction rate enhances or retards. Since the coefficient of segregation, \(I_{s}\), of a reaction is exactly the dimensionless (relative) covariance of the concentrations of the reactants, its value is positive when both reactants have collocated sources and is negative when the reactants originate from sources affected mainly by opposed motions.  
Figure 5a shows, via the coefficient of segregation, the effects of turbulence on the reaction rates as simulated in the TKM for the reactions detailed in Table 1 (e.g., the segregation between NO and O\({}_{3}\), between NO and HO\({}_{2}\), and between RH and OH, etc.). Even though the chemical reaction chains tend to cause a balance between the production and the destruction of several species, large segregation appears for reactions involving the emitted species NO and RH. These effects permit the NO and RH concentrations to increase continuously after the early periods of decrease as discussed above. In the following discussion, the important reaction pairs have negative segregation coefficients. We will refer to their absolute values in percent, so that a minimum value in \(I_{s}\) is referred to as a maximum segregation. The vertical profiles (Figure 5a) of \(I_{s}\) for the most segregated reactions show consistency through most of the CBL. Segregations are generally larger near the top and bottom boundaries than in the bulk of the CBL. Figure 5b delineates the variation of \(I_{s}\) with time in the top, bottom and middle layers. For the NO + O\({}_{3}\) reaction, the values of \(I_{s}\) in all layers reach minima (largest negative values) at 20 min and then, except for the top layers, increase to about 15 %. In the top layer, segregation larger than 45 % remains at 200 min. This segregation accounts for the NO concentration in the top layer being larger than in the bottom layer. It is evident that the emission rate of NO is sufficient to keep the photochemical chain reactions from reducing the segregation of NO and O\({}_{3}\) to the point where average chemical kinetics prevails (\(I_{s}=0\)). In the case of the RH + OH reaction, the source strength of RH is sufficient to keep segregations greater than 50% throughout the CBL after the first 20 min because HO\({}_{2}\) is produced by this reaction. The segregation of NO and HO\({}_{2}\) shows a similar pattern.  
Figure 5: Segregation coefficients between reactive species at three layers (surface layer, SL; middle layer, ML; top layer, TL) with times of 10, 20, 30, 60, 120, and 200 min: (**a**) Vertical distribution and (**b**) Temporal behavior  
All other reaction pairs shown in Figure 6 have very small segregations (some positive and some negative) throughout the CBL with the exception of NO\({}_{2}\) and OH in the top layer where they increase (negatively) with time and reach about \(-0.55\) at 200 min. The rates of those reactions with small \(I_{s}\) values are thus nearly what would be given by the conventional kinetic expression.