A “huge” ozone hole that was not expected to exist has been identified in the Earth’s atmosphere over most of the tropical region.
The hole is a year-round open space in the planet’s ozone layer and is seven times larger than the better-known Antarctic ozone hole that opens each spring.
Professor Qing-Bin Lu, a scientist from the University of Waterloo in Ontario, Canada, said that according to his research, the hole has already been present for more than 30 years and covers an area so large that half of the population world could be affected.
He said The Independent“Unlike the Antarctic ozone hole, which only appears in the spring, the tropical ozone hole has appeared in all seasons since the 1980s, and its area is about seven times larger.
“[It] could cause global concern as it may lead to increased UV radiation at ground level and associated risks of skin cancer and cataracts, as well as other negative health and ecosystem effects in tropical regions.
He said there are “preliminary reports showing that levels of ozone depletion in equatorial regions are already endangering large populations, and that the associated UV radiation reaching the regions was far greater than intended”.
Speaking about the discovery of the huge ozone depleted area, Professor Lu said The Independent“It seems incredible that the Great Tropical Ozone Hole has not been discovered before. But there are inherent challenges to making this discovery.
“First, no tropical ozone hole should exist according to prevailing photochemical theory. Second, unlike Antarctic/Arctic ozone holes which are seasonal and appear mainly in the spring, the tropical ozone hole is essentially unchanged in the with the seasons and is therefore invisible in the original observational data.
As with the Antarctic ozone hole, the normal ozone value was found to be depleted by about 80% at the center of the tropical ozone hole, according to the research.
The new research also highlighted differences in the prevailing theories about how ozone is depleted.
In the past, the presence of chlorofluorocarbons (CFCs) was considered the main cause of ozone layer depletion. The 1987 Montreal Protocol, which banned them, saw a major reduction 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 in 2020-2021.
“This was unexpected from all photochemistry-climate models,” Prof Lu said.
A separate theory of ozone depletion, known as cosmic ray-induced electronic reaction (CRE), in which cosmic rays from space reduce ozone in the atmosphere, has been first proposed by Professor Lu and his colleagues two decades ago.
He said The Independent: “The observed results strongly indicate that the Antarctic and tropical ozone holes must arise from an identical physical mechanism, and that the CRE mechanism showed excellent agreement with the observed data.”
He added: “CFCs are undoubtedly the main ozone-depleting gases, but cosmic rays play a major triggering role in the formation of polar and tropical ozone holes.”
The research is published in the journal AIP Advances.