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"Jill 1¬Ľ, lllljllflllljllf

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250 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 Wavelength (nm)

250 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 Wavelength (nm)

FIGURE 16.6 Spectral irradiation of unfiltered solar simulator compared to zero air mass solar spectral irradiance (adapted from Winer et al, 1979).

Determining kx is not as simple as measuring the loss of N02, however, since secondary reactions of the O and NO produced in (f) lead to nonexponential decays of N02. Thus plots of ln[N02] against irradiation time are observed to be curved. In early smog chamber studies, a parameter known as kd was reported as a measure of the light intensity, where /cd was defined by

*d was thus obtained experimentally by extrapolating the NOz concentration-time profile back to the beginning of the irradiation, t = 0.

Since kt is the fundamental parameter of interest, however, there has been emphasis on measuring and reporting k{ rather than kd in smog chamber studies. A procedure for determining k{ from measured rates

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