Speaker: Aaron Match (NYU)
Topic: Explaining ozone layer structure and self-healing

The absorption of ultraviolet light by the ozone layer causes it to continually break apart and reform. A survey of atmospheric chemistry textbooks reveals mixed messaging as to whether this continual photolysis of ozone has a null effect on ozone concentrations (as when ozone is explained to maximize where its source maximizes between abundant photons aloft and abundant O2 below) or a suppressing effect (as when ozone is explained to result from competition between the photolytic source and sink). These mixed messages are shown to correspond to different regimes of ozone destruction: a photolytic sink regime that occurs for the classical Chapman Cycle or under catalytic destruction of atomic oxygen, and a non-photolytic sink regime under catalytic destruction of ozone. Today's tropical atmosphere is estimated to be in a photolytic sink regime above roughly 40 km and a non-photolytic sink regime below. These regimes have qualitatively different mechanisms for producing ozone structure and sensitivities to perturbations. Existing theories of the ozone response to depletion aloft are formulated in the non-photolytic sink regime, predicting increased ozone below known as self-healing. We present a new theory in the photolytic sink regime, predicting self-amplified destruction above 40 km, as corroborated by a chemistry-climate model. This self-amplified destruction is linked to gross features of the UV absorption spectra for O2 and O3. Within the non-photolytic sink regime, a new mechanism is proposed for how tropospheric expansion under global warming can lead to reductions in tropical lower stratospheric ozone.