Photolysis Frequencies of Nitrogen Dioxide and Ozone: Measurements and Model Calculations

Abstract

Photolysis of ozone at wavelengths below 320 nm is the main source of tropospheric OH radicals:

$${O_3} + hv \to O{(^1}{\text{D}}) + {O_2}$$

((1))

$$O{(^1}{\text{D}}) + {H_2}O \to 2\;OH$$

((2))

Photolysis of nitrogen dioxide occurs in the wavelength range below 420 nm and is the basic supposition of tropospheric ozone production:

$$N{O_2} + hv \to NO + O{(^3}{\text{P}})$$

((3))

$${O_2} + O{(^3}{\text{P}}) \to {O_3}$$

((4))

The reaction rate constants of the photolytic processes (1) and (3) are given by the photolysis frequencies J(O₃) and J(NO₂). An accurate knowledge of these quantities is the basis for numerical modelling of photochemical reaction cycles.