The ozone layer is mainly found in the lower portion of the stratosphere, from approximately 15 to 35 km Credit: EastMojo Image

Ozone (O3) is a gas made up of three oxygen atoms. It occurs naturally in small (trace) amounts in the upper atmosphere or the stratosphere. Ozone protects life on Earth from the Sun’s ultraviolet (UV) radiation. In the lower atmosphere (the troposphere) near the Earth’s surface, ozone is created by chemical reactions between air pollutants from vehicle exhaust, gasoline vapors, and other emissions. At ground level, high concentrations of ozone are toxic to people and plants.

A Brief History of the Ozone layer

In 1974, American Scientists Mario Molina and F. Sherwood Rowland at the University of California, Irvine, published an article on how human activities produced chlorofluorocarbons (CFCs)—molecules containing only carbon, fluorine, and chlorine atoms—could be a major source of chlorine in the stratosphere. During that time, CFCs were used as aerosols sprays and coolant in refrigerators. When the CFCs released reached the stratosphere, sun’s UV rays break CFCs down into substances that include chlorine.

Researchers later discovered that bromine and certain bromine-containing compounds, such as bromine monoxide (BrO), were even more effective at destroying ozone than were chlorine and its reactive compounds. These harmful chemicals were main source of Ozone depletion.

Ozone depletion is gradual thinning of Earth’s ozone layer in the upper atmosphere. The thining of Ozone layer causes harmful ultraviolet (UV) radiation from the Sun to enter the earth’s surface and damage plants, animals and humans ranging from crop death to skin cancer.

Course of Action

On September 16, 1987, scientists, leaders and policymakers from around the globe made an International agreement called The Montreal Protocol. The agreement was designed to stop the production and import of ozone depleting substances and reduce their concentration in the atmosphere to help protect the earth’s ozone layer. Therefore, September 16 marks the International Day for the Preservation of the Ozone Layer.

The Montreal Protocol is widely considered as the most successful environment protection agreement.

The Montreal Protocol sets binding progressive phase out obligations for developed and developing countries for all the major ozone depleting substances, including chlorofluorocarbons (CFCs), halons and less damaging transitional chemicals such as hydrochlorofluorocarbons (HCFCs). The Montreal Protocol targets 96 ozone depleting chemicals in thousands of applications across more than 240 industrial sectors.

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Stage of Recovery

After 33 years, since the Montreal Protocol, the ozone hole is showing its first signs of recovery but it could take more than a decade to completely heal. Strahan and her colleague Anne Douglass published one of the first studies in 2018 confirming that atmospheric chlorine levels are falling in step with reduced ozone depletion over Antarctica—proof that the Montreal Protocol is working.

NASA monitors ozone from space using the Microwave Limb Sounder (MLS) and Ozone Monitoring Instrument aboard its Aura spacecraft, and the MLS also measures trace gases containing chlorine.

“When it comes to a clear sign the ozone hole is going away, it could still be a couple decades before we can look up and say it’s smaller every single year than it was in the early 2000’s,” Strahan said. We’re going to have that kind of variability going forward, but once we get to 2040 or so, there will be so much less chlorine that the holes will be smaller even in cold years. It will be a long, bumpy road, but we’re headed in the right direction. We just need to be patient and keep up the good work.”

1979: The purple and blue colors are where there is the least ozone, and the yellows and reds are where there is more ozone.
March 30, 2020: The purple and blue colors are where there is the least ozone, and the yellows and reds are where there is more ozone.

But scientist say that it is unlikely that the hole, which had been had been about three times the size of Greenland, healed because of the impact of the worldwide coronavirus lockdowns. According to recent data from the National Aeronautics and Space Administration (NASA), ozone levels above the Arctic reached a record low in March.

Today, even as we continue to battle Ozone depletion by replacing harmful CFCs with hydrofluorocarbons(HFCs) that do not deplete the Ozone but HFCs are greenhouse gases that trap heat and contributes to global warming and climate change.

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