The hole in the ozone layer which forms annually on Antarctica has grown for the third consecutive year. At nearly 10 million square miles (26.4 million square kilometers), the ozone hole is the largest since 2015.
But despite this growth, scientists say the hole size is still in an overall downward trend.
“All the data says ozone is on the mend,” said Paul Newman, chief earth scientist at NASA’s Goddard Space Flight Center. Associated Press (opens in a new tab).
Ozone is made up of three oxygen atoms and makes up very little of our atmosphere, but it has a huge impact on our planet. The blanket-like layer that spans the globe absorbs the most harmful ultraviolet (UV) radiation since Sunshielding of land life. Ozone forms in the stratosphere, 9 to 18 miles (14.5 to 29 kilometers) above the earth’s surface. It is formed when UV radiation splits normal oxygen molecules, which are made up of two oxygen atoms (O2); the two floating oxygen atoms then each bond with one oxygen molecule, forming a molecule made up of three oxygen atoms.
Scientists discovered the thinning ozone layer over Antarctica in the early 1980s. Although ozone is naturally created and destroyed in the stratosphere, man-made pollution destroys ozone faster than it can form. In particular, industries that use chlorine or bromine, such as refrigeration and air conditioning, destroy ozone at alarming rates. In the stratosphere, chlorine molecules react with ozone to create a chlorine monoxide molecule (made up of a chlorine atom and an oxygen atom) and an O2 molecule. Then the chlorine monoxide molecule breaks down, releasing that chlorine atom to react with more ozone. According to the Environmental Protection Agency, one chlorine atom can destroy 100,000 ozone molecules before that chlorine molecule is removed from the atmosphere.
Substances such as chlorofluorocarbons, used in refrigeration and air conditioning, remain in the atmosphere for a long time, some for more than six months, which means that the chlorine and other chemicals in these substances can wreak havoc on the ozone layer.
The ozone hole was first observed in the early 1980s and reached its maximum extent in 2006, according to NASA. This year’s ozone hole, which peaked on October 5, was the largest recorded since 2015. But scientists aren’t too worried.
“The general trend is improvement. This year is a little bit worse because this year was a little bit colder,” Newman told the AP.
A cold stratosphere is exactly what chemicals like chlorine need to break down ozone. During the Antarctic winter, the stratosphere becomes cold enough for clouds to form. The ice crystals that make up those clouds provide a surface on which chlorine, for example, can react with ozone. As spring approaches September, the sun’s UV rays trigger these reactions. Once summer is in full swing, the stratosphere heats up enough for the clouds to evaporate, removing the surface on which the ozone-destroying chemical reactions take place.
Global agreements such as the Montreal Protocol (opens in a new tab)which regulates the production and consumption of ozone depleting substances, have helped to repair the ozone hole And despite the increasing size of the ozone hole this year, scientists generally agree that the hole is shrinking.
Earlier this year the National Oceanic and Atmospheric Administration reported that ozone-depleting substances in the atmosphere decreased by 50 (opens in a new tab)% since 1980. The report also notes that if this downward trend continues, the ozone layer could be completely repaired by 2070.