A ‘huge’ ozone hole that was not expected to exist has been identified in the Earth’s atmosphere over almost the entire tropical region.
The hole is a year-round gap in the planet’s ozone layer and is seven times larger than the more famous Antarctic ozone hole, which opens every year in the spring.
Professor King-Bin Lu, a scientist at the University of Waterloo in Ontario, Canada, said that according to his research, the sinkhole has existed for more than 30 years and covers such a massive area that half the world’s population could be affected.
He told The Independent: “Unlike the Antarctic ozone hole, which only appears in the spring season, the tropical ozone hole has appeared in all seasons since 1980 and its area is approximately seven times larger.
“[It] may be of global concern because it may cause an increase in ground-level ultraviolet radiation and the associated risks of skin cancer and cataracts, as well as other negative effects on health and ecosystems in tropical regions.
He said there were “preliminary reports indicating that levels of ozone depletion over equatorial regions are already endangering large populations there and the associated ultraviolet radiation reaching the regions is much greater than expected.”
Speaking about the discovery of the vast area of depleted ozone, Professor Lu told The Independent: “It sounds amazing that the large tropical ozone hole has not been discovered before. But there are some inherent challenges in making this discovery.
“First, basic photochemical theory does not expect a tropical ozone hole to exist. Second, unlike the Antarctic/Arctic ozone holes, which are seasonal and occur mainly in spring, the tropical ozone hole is essentially unchanged over the seasons and is therefore invisible in the original observed data.
As with the Antarctic ozone hole, the normal value of ozone was found to be reduced by approximately 80 percent in the center of the tropical ozone hole, the study found.
The new research also highlighted differences in prevailing theories about how ozone is depleted.
In the past, the presence of chlorofluorocarbons (CFCs) was considered the biggest cause of ozone depletion. The Montreal Protocol of 1987, which banned them, saw a significant decrease in their use.
But despite the global ban, the largest, deepest and most persistent ozone holes – over Antarctica – were still observed in the late 2000s and into 2020-2021.
“This was unexpected from any photochemistry-climate models,” Professor Lu said.
A separate theory of ozone depletion, known as the cosmic ray-driven electron reaction (CRE), in which cosmic rays from space reduce ozone in the atmosphere, was first proposed by Professor Lu and his colleagues two decades ago.
He told The Independent: “The observed results strongly suggest that both the Antarctic and tropical ozone holes must arise from an identical physical mechanism and that the CRE mechanism has shown excellent agreement with the observed data.”
He added: “CFCs are undoubtedly the main ozone-depleting gases, but cosmic rays play a major driving role in causing both the polar and tropical ozone holes.”
The research was published in the journal AIP Advances.
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