M

03 + M) must be consid ered and the kinetic expression for k, is more complex.

Of course, k{ is not an absolute light intensity measurement per se but merely an indication of the intensity in one of the wavelength regions of interest for atmospheric chemistry. It has the advantage of being simple, convenient, and inexpensive, since only monitoring instruments for N02 are needed and these are generally standard components of the analytical apparatus. The disadvantage is that a number of photo-chemically active species (e.g., 03 and HCHO) have absorption coefficients and wavelength dependencies different from N02 and, for these, kx will not necessarily be a good measurement of the rates of their photochemical reactions, depending on the spectral distribution of the light source.

Direct measurements of light intensity using radiometers as described in Chapter 3.2 can also be made.

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