Contribution of excited ozone and oxygen molecules to the formation of the stratospheric ozone layer

Abstract

The absorption of UV, visible and near IR radiation by O3 produces transient, electronically excited O3. The absorption of thermal IR radiation (λ = 9.065, 9.596 and 14.267 μm) produces vibrationally excited O3 molecules. Thermal absorption is likely the main factor in the self-decay of O3. Photoexcitation of ground state O2(X3Σg-) by IR and red light radiation produces singlet oxygens (O2 (a1Δg) and O2 (b1Σg+)). Chemical reactions in the stratosphere produce them as well. When reacting with ozone, singlet oxygen produces O (3P) andO2 (X0Σg-). By doing so, they tend to maintain the prevailing ozone concentration and are thereby important for the stability of the ozone layer. During the daytime, O (1D), O2 (a1Δg) and O2 (b1Σg+) reach their maximum concentrations at altitudes of 45 to 48 km. This manifests fast ozone turnover which generates the maximum stratospheric temperature at those particular altitudes. During the night-time, the self-decay of ozone and absorption of light fromthe nightglows, moon and stars by O3 and O2 generates so much heat that the stratospheric temperature decreases by only a couple of degrees. Being a heavier gas than O2 and N2, ozone lacks buoyancy in the atmosphere, and it starts to descend immediately when formed. Chapman calculated that ozone in the stratosphere would descend 20 m per day. At the North and South Poles, during the four to six months of darkness in the winter, ozone descends by 2.4 to 3.6 km. This descent is likely the main reason for the stratospheric ozone depletion above the poles during winter.