New Measurements of Hydroxyl in the Middle Atmosphere Confound Chemical Models

The drive to measure, understand, and prevent ozone depletion over Antarctica has been so intense and attention-grabbing that the words “ozone” and “hole” now seem mated for life. But the ozone layer, which is densest at altitudes of 15–20 km, envelops the entire planet and extends into the mesosphere, where it plays a key role in the atmosphere's physics and chemistry. Ozone molecules, heated by their absorption of ultraviolet photons from the Sun, provide most of the energy that drives circulation in the upper stratosphere and mesosphere. (Figure 1 depicts the vertical structure of the atmosphere.)