Naturally occurring halogens, such as bromine and iodine, emitted by the oceans and other ecosystems, have not only played a fundamental role in the destruction of the ozone layer over the past century, but also contribute to delaying its recovery.
This is the conclusion of an international study led by the Blas Cabrera Institute of Chemical-Physics (IQF-CSIC), which demonstrated for the first time that natural halogens, such as these chemical compounds, helped degrade the natural shield protecting the planet from ultraviolet radiation.
The study, published in Nature Communications, shows that natural halogens, despite being far less abundant than those of anthropogenic origin, play a crucial role in the past and future of the ozone layer, reported this Wednesday by the Efe agency.
Using climate simulations, the team calculated the evolution of stratospheric ozone from the early 20th century to the end of the 21st century.
The scientists found that emissions of chlorine- and bromine-containing compounds of anthropogenic origin caused a significant decline in ozone levels during the 20th century (including the formation of the Antarctic ozone hole).
They also calculated the relative contribution of natural halogens compared with anthropogenic ones to the destruction of ozone.
The team observed that, during the peak period of anthropogenic ozone destruction (1990-2020), natural halogens were responsible for approximately 15% of the total ozone loss induced by halogens across the entire stratosphere.
Their impact is particularly significant in the lower stratosphere, where they were responsible for nearly half of ozone destruction in extratropical regions, the study notes.
“Although their abundance is much lower than that of anthropogenic halogens, natural bromine and iodine are extraordinarily efficient at destroying ozone. Our simulations show that their contribution has been crucial, even during the decades when the compounds regulated by the Montreal Protocol had their greatest impact,” explained Julián Villamayor, a researcher at IQF-CSIC and the study’s lead author.
The study also found that natural halogens amplify the chemical processes responsible for stratospheric ozone depletion at the edges of the Antarctic ozone hole and contribute to the increase in solar radiation reaching the Earth’s surface.
Moreover, according to the study’s calculations, these compounds cause the seasonal variations associated with the ozone hole to occur earlier and delay the recovery of the Antarctic ozone cycle by about 50 years, compared with simulations that do not account for their presence.
Although measures driven by the Montreal Protocol continue to promote the recovery of the ozone layer, natural sources of halogens contribute to delaying its total recovery by several decades, the authors warn.
