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sirm total stratospheric loss rate total atmospheric burden total stratospheric loss rate total atmospheric burden

Chapter 3 Ozone Production and Loss

3.1 Chapman Chemistry

The first successful attempt to quantitatively understand the photochemistry of ozone (O,) was made by Chapman in 1930 [63j. He proposed that O-, is created by the dissociation of O , to form O atoms, followed by the reaction between O and 02:

Most of the photolysis of 02 in the stratosphere occurs at wavelengths in the Schumann-Runge bands (175-200 nm) and the Hertzberg continuum (extending to 242 nm) [641.

O, is destroyed by ultraviolet photons:

O produced in reaction (3.4) can be in one of two electronic states: P ("triplet P") or 'D ("singlet D"). O('D) is an excited electronic state, and is produced when the incident photon has a wavelength of less than -300 nm. For wavelengths longer than -325 nm, the O atom is produced in the ground state O('P). For incident photons with wavelengths between 300 and 325 nm, both O('D) and Of P) are produced [65] (see also DeMore et al. [5], Table 8). Because of their higher internal energy, O('D) atoms are more reactive than 0(,P).

O('D) is rapidly converted to O('P) through collisions with molecules such as 02 and C02. As a result, the abundance of O('D) is between 10 6 and 10 7 of the abundance of G( lP) in the stratosphere. We will hereafter refer to O('P) atoms simply as O atoms; reactions specifically requiring Oi'D) atoms will be so designated. The last important Chapman reaction is the direct reaction between O, and O:

in addition to these, Chapman discussed several other reactions now known to be unimportant. This set of reactions, known as the Chapman reactions, form the cornerstone of stratospheric O, chemistry.

3.2 The Odd-oxygen Family

Considering just the Chapman reactions, the lifetimes \/L of O, and O for typical mid-latitude lower-stratospheric conditions are

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