General Description of Atmospheric Chemistry

Abstract

In contrast with the atmospheres of the other planets, Earth’s atmosphere contains oxygen. Oxygen was not present in the primitive atmosphere that existed more than 2 billion years ago, but resulted from the development of biological processes at the Earth’s surface; simultaneously with O₂, ozone molecules, O₃, appeared in the atmosphere. Ozone is of prime importance in all parts of the Earth’s atmosphere. Although ca. 90% of ozone is present in the upper atmosphere (stratosphere), where it strongly absorbs solar UV radiation, the ozone content of the lower atmosphere (troposphere) contributes to the oxidative capacity of this region. The long-term trends of ozone are now established, indicating a decrease in the stratosphere and an increase in the global troposphere. The lack of compensation is due to the very limited exchange of air between these two atmospheric regions. In fact, a main feature of the atmosphere is the strong coupling that exists between chemistry and dynamics.