Mesosphere, ozone formation

Thus, when studying atmospheric chemistry, it is necessary always to take into account the vertical and horizontal movements in the atmosphere, as well as the conditions controlling those chemical reactions that do not spontaneously lead to photochemical equilibrium. These conditions are applicable not only to ozone in the lower stratosphere, but also to atomic oxygen in the upper mesosphere above 75 km. In fact, equation (4) shows that, with increasing height, the formation of O3 becomes less and less important because of the decrease in the concentration of 02 and N2. Above 60 km the concentration of atomic oxygen exceeds that of ozone, but it is still in photochemical equilibrium up to 70 km. However, at the mesospause (85 km), it is subject to atmospheric movements, and its local concentration depends more on transport than on the rate of production. 

Photolysis of O3 in the Hartley bands leads to 02( Ag) production, with 60% formed vibrationally excited,and under atmospheric conditions quenching is found to be a rapid process. Rates of formation of 02( Ag) by this mechanism in the upper atmosphere of Venus have been calculated and compared with those determined by observations of the 02( Ag) emission at 1.27 pm for the values to agree, the previously accepted ozone concentrations would have to be revised upwards by a factor of 10. In the terrestrial atmosphere, the photolysis of 1 6q 1 8q at wavelengths between 170—205 nm could be an important source of odd oxygen in the high stratosphere and mesosphere, as solar radiation not absorbed by discrete 02 features may penetrate these regions and photolyse the minor isotopic constituent (present as 4% of naturally occurring 02). ... 

Reaction (5.16) refers to the Herzberg continuum (230-280 nm), which consists of three bands. It is clear that O3 formation (reaction 5.14) as well as O3 photolysis occurs. Hence, at 30 km (above the peak in the ozone layer), we observe substantial reductions in the amount of radiation received between 225 and 275 nm. The O2 photodissociation in the Schumann-Runge continuum (125-175 nm) directly produces O ( D) and opens many radical reactions (but almost all molecules photodisso-ciates at such hard radiation) this is in altitude of 100-200 km. The solar H Ly-man-a line (121.6 nm) is, through O2 photodissociation, an important source of O ( D) production throughout the mesosphere and lower thermosphere. 

The prime driver of the chemical system of the earth s atmosphere is photochemical reactions caused by solar radiation. The atmosphere of the earth is divided into levels called the troposphere, stratosphere, mesosphere and thermosphere from nearest the ground to farthest according to the characteristics of the temperature gradient as shown in Fig. 3.1. The cause of the temperature inversion in the stratosphere, which characterizes the earth s atmosphere, is the formation of an ozone layer by the photolysis of oxygen, one of the major components of the atmosphere. In this chapter, the spectrum of solar radiation, actinic flux, and so on, that is necessary to calculate the photolysis rate of atmospheric molecules are explained. 

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