Stratosphere Temperature Profile Maintained by Photoionization

The question asks which atmospheric layer's temperature profile is maintained by the photoionization of gas molecules. Photoionization involves the removal of an electron from an atom or molecule by absorbing photons.

Understanding Atmospheric Heating Mechanisms

Different atmospheric layers have distinct temperature profiles due to various energy absorption processes:

• Troposphere: Heated from below by the Earth's surface; temperature decreases with altitude.
• Stratosphere: Heated from above by the absorption of ultraviolet (UV) radiation, primarily by ozone. This heating causes the temperature to increase with altitude.
• Mesosphere: Temperature decreases with altitude.
• Thermosphere: Heated by direct absorption of high-energy solar radiation (X-rays and extreme UV), causing significant ionization and very high temperatures, although the air is extremely thin.

Role of Photoionization in the Stratosphere

The primary process maintaining the Stratosphere temperature profile involves ozone ( $O_3$ ) absorbing harmful UV radiation from the sun. While direct photoionization (creating ions and free electrons) is most significant in the thermosphere, the absorption of UV photons by ozone molecules leads to their dissociation and subsequent recombination, releasing heat. This absorption process is fundamental to the stratosphere's temperature structure, where temperature increases with height. The term 'photoionization' in the question likely broadly refers to photo-chemical processes driven by solar radiation that affect the temperature profile, with ozone's UV absorption being the key mechanism in the stratosphere.

Conclusion

The absorption of solar UV radiation by ozone molecules, a process related to photo-chemistry and energy transfer, is responsible for the temperature profile of the Stratosphere.

Answer Summary

The correct option is the one corresponding to the Stratosphere.