Azusa levels

Figure 33 shows the reactive hydrocarbon history starting at Azusa at 0730 and ending at El Monte at 1030 on September 29, 1969. Despite the sharp reduction in hydrocarbon fluxes, the calculated curve stays above the Azusa levels until 1000 hours when it begins to slope-off in the observed manner. The model output clearly bears a closer relationship to the Azusa measurements than it does to the El Monte observations. This problem is typical of the difficulties we encountered in attempting to model conditions at the eastern portion of the basin at El Monte. 

The NO2 behavior on Figure 35 exhibits more nearly what one would expect than do either the reactive HC or the NO. Proceeding from the end of its transient adjustment to observed sunlight intensity, the air mass gradually undergoes NO2-transition from Azusa levels to El Monte levels as it meanders about in the northeastern area of the basin. Nitric oxide conversion supported by increasing sunlight intensities drives the NO2... 

History Analysis of the 1030 El Monte Trajectory. Because of the relative completeness of initial conditions that we can relate to the Azusa station, we have chosen the 1030 trajectory to discuss in some detail. Examining Table VII, we note an overabundance of ozone at 1030 and a correspondingly rapid completion of NO NO2 conversion. Reactivity analyses (see Atmospheric Adaptation) and our early modeling studies suggest reduction of the oxidation rate constants. To achieve some level of comparative assessment with the previous work, we assign one-fourth the nominal NO flux and one-half the oxidation rate thus, f = 1/4 and r = 1/2 describe the conditions as before. This time, however, we preserve the HC/NOa,-ratio as in the entries in Table VII and reduce hydrocarbon fluxes by a factor of two. This means that the difference in end-point concentrations between this case and the 1/4< no, 1/2< hc entries results solely from the rate constant reduction. This differs from the earlier work where hydrocarbon fluxes were not reduced. 

On Figure 34 we note a sharp drop from the interpolated NO-level between 0730 and 0740 hours. This reflects the previously noted failure of the data to approach quasi-equilibrium between NO, NO2, O3, and sunlight intensity under high-oxidant conditions. The NO-conversion seems to proceed at roughly the observed rate after the transient is absorbed in the system however, the level ends up closer to Azusa values than to El Monte values. If we were to use 0830 El Monte concentrations as initial values, we would have a lower HC/NO-ratio and could expect still slower nitric oxide conversion rates. Thus, nitric oxide and hydrocarbon decay more like the Azusa data than the El Monte data. 

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