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Irradiation time (min)

FIGURE 16.12 Concentrations of OH as a function of irradiation time during irradiation of a VOC-NOA. mixture in the evacuable smog chamber of Fig. 16.3. The initial conditions were as follows: [NO],, = 0.5 ppm, [NO2]0 = 0.12 ppm, [C3HS]„ = 0.013 ppm, [C3H6]0 = 0.010 ppm, [HCHO]„ = 0.02 ppm, T = 303 K, RH = 50%, &,(N02 photolysis) = 0.49 min~'. Bars are experimental data; see text for description of curves A-D (adapted from Carter et al., 1982).

OH as a function of time when a VOC-NOx mixture was irradiated in the evacuable smog chamber shown in Fig. 16.3 (Carter et al., 1981, 1982). The rates of decay of propane and propene were used to estimate the concentration of OH shown by the horizontal bars in Fig. 16.f 2 as a function of reaction time.

In this system the concentrations of propane, propene, and formaldehyde were kept sufficiently small that the predominant reactions were those of the NOx species. By keeping the NO concentrations high, 03 concentrations could be kept low because reaction (8) is fast:

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