What is it about?

The stratospheric ozone layer absorbs harmful ultraviolet (UV) radiation and is therefore a vital protection layer to living creatures on the Earth’s surface. However, cosmic rays from deep space may destroy the ozone layer, especially when there are significant chlorofluorocarbons (CFCs) in the atmosphere. Basing on their laboratory findings, Dr. Lu and co-workers previously proposed a cosmic-ray-driven electron-induced reaction (CRE) mechanism for the formation of the Antarctic ozone hole. In this study, Dr. Lu now derives a concise and elegant equation from the CRE theory. This equation enables parameter-free analytical calculations of ozone loss in the lower stratosphere across the globe from the polar regions to mid-latitudes and the tropics. The calculated results not only exhibit excellent agreement with observations but also validate Dr. Lu’s recent discovery for the first time of the ozone hole over the tropics that has existed in all seasons since the 1980s. The latter has a depth similar to that of the well-known Antarctic hole that usually only appears in springtime, but its area is seven times larger.

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Why is it important?

Ozone depletion has been a subject of intense research over the past 4-5 decades, based mainly on chemistry-climate models (CCMs) evolved from the Nobel Prize winning Molina-Rowland photochemical theory of CFCs. CCMs are able to reproduce the observed small ozone loss by a few percent in the upper stratosphere around 40 km from the ground, indicating good understanding of the underlying science for ozone depletion in this altitude range. However, large discrepancies between CCMs and observations persistently exist in the lower stratosphere below 25 km, in which ozone holes up to about 80% ozone losses at hole centers over the Antarctic and the tropics are found. In particular, the uncertainties in ozone change trends from both CCMs and observations are very large (up to +/-20% per decade) in the lowermost stratosphere around 15 km. New research has therefore been called to put the ozone trend results in the lower stratosphere on more solid ground. Moreover, researchers have also questioned Dr. Lu’s surprizing discovery of the largest and all-season ozone hole over the tropics in 2022. By quantifying several atmospheric processes in the CRE theory for ozone depletion, this study makes a remarkable work that leads to an analytical formulation, producing the atmospheric concentration of chlorine atomic radicals and hence providing a capacity of quantifying ozone depletion in the global lower stratosphere and even troposphere. "This work is a tour de force", one of the reviewers commented. It represents a landmark contribution to understanding global ozone depletion, including validation of the tropical ozone hole, and the impact of cosmic rays on the Earth’s living environment.


There is a great challenge in quantifying ozone depletion in the global lower stratosphere to reproduce the observed results. Atmospheric researchers typically aim to resolve this issue by running CCMs with addition of more complexities such as the effects of greenhouse gases and changing air circulation patterns. By successfully reproducing the ozone depletion rates in various regions of the global lower stratosphere, this study demonstrates that the formulated CRE theory with inputs of the concentrations of anthropogenic ozone depleting substances and the intensity of natural cosmic rays can effectively remove the persistent discrepancies between CCMs and observations, especially in the lowermost stratosphere. It is also of great importance to further study the largest, year-round ozone hole over the tropics that constitutes half the Earth’s surface area and is home to about half of the world's population.

Professor Qing-Bin Lu
University of Waterloo

Read the Original

This page is a summary of: Formulation of the cosmic ray–driven electron-induced reaction mechanism for quantitative understanding of global ozone depletion, Proceedings of the National Academy of Sciences, June 2023, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2303048120.
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