oxygen molecules are present in mesosphere and in thermosphere also then why ozone formation happens only in stratosphere

The formation of ozone occurs primarily in the stratosphere for a few reasons:

1. Presence of Solar Radiation: The stratosphere is the layer of the atmosphere that absorbs the majority of the Sun's harmful ultraviolet (UV) radiation. This UV radiation is necessary for the formation of ozone. It splits oxygen molecules (O2) into individual oxygen atoms, which can then combine with other oxygen molecules to form ozone (O3).

2. Temperature Gradient: The temperature in the stratosphere increases with altitude, unlike in the troposphere (the layer below the stratosphere) where it decreases with altitude. This temperature inversion is due to the absorption of UV radiation by ozone, which generates heat. This heat prevents the ozone from sinking into the troposphere and keeps it in the stratosphere.

3. Concentration of Oxygen: The stratosphere has a higher concentration of oxygen than the mesosphere and thermosphere. This is because the majority of the Earth's atmospheric oxygen is found in the troposphere and stratosphere. The higher concentration of oxygen in the stratosphere allows for more ozone to be produced.

4. Lower Atmospheric Pressure: The atmospheric pressure in the stratosphere is lower than in the troposphere, which allows the oxygen molecules to be more spread out and increases the likelihood of an oxygen molecule colliding with an oxygen atom (created by the splitting of an oxygen molecule by UV radiation) to form ozone.

In the mesosphere and thermosphere, the conditions are not as favorable for ozone formation. The concentration of oxygen is lower, the temperature is lower (in the mesosphere) or much higher (in the thermosphere), and there is less UV radiation available to split oxygen molecules into atoms. Therefore, most of the ozone in the Earth's atmosphere is found in the stratosphere.