In the lower stratosphere over the tropics, scientists discovered a large, all-season ozone hole comparable in depth to the well-known springtime Antarctic hole, but roughly seven times larger in size. Both Antarctic and tropical ozone holes exhibit the same physical mechanism that could be driven by cosmic-ray-driven electron reactions.

Qing-Bin Lu, of the University of Waterloo in Ontario, Canada, reports in AIP Advances that a large, all-season ozone hole exists in the lower stratosphere over the tropics, comparable in depth to the well-known springtime Antarctic hole, but with roughly seven times the area.

Half of the planet's surface area and half of its population live in the tropics, according to Lu. Globally, the tropical ozone hole may be of great concern.

'Ozone depletion increases the risk of skin cancer and cataracts in humans, weakened human immune systems, decreased agricultural productivity, and negatively affects sensitive aquatic organisms and ecosystems.'

Scientists in the scientific community were surprised when Lu observed the ozone hole since conventional photochemical models did not predict it. Both Antarctic and tropical ozone holes exhibit the same physical mechanism that is based on cosmic-ray-driven electron reactions. 

Similar to the polar ozone hole, the tropical ozone hole depletes approximately 80% of its normal ozone value. Ozone depletion levels over equatorial regions are already endangering large populations, with UV radiation reaching these regions far greater than expected.

During the 1970s, atmospheric research suggested that industrial chemicals, primarily chlorofluorocarbons (CFCs), were depleting the ozone layer, which absorbs most of the sun's ultraviolet radiation.

CFC-caused ozone depletion was confirmed by the discovery of the Antarctic ozone hole in 1985. Bans on such chemicals have helped slow ozone depletion, but evidence suggests it continued.

Tropical and polar ozone holes, as well as three 'temperature holes' in the global stratosphere, play a major role in cooling and regulating stratospheric temperatures, according to Lu. This finding may prove crucial to understanding global climate change, he said.

Lu's discovery builds on the ozone-depleting mechanism proposed about two decades ago by CRE and his colleagues.

'Ozone depletion, UV radiation change, cancer risks, and other negative effects on health and ecosystems in tropical regions must be carefully studied,' said Lu.