What is going on with the ozone layer?

The healing of the ozone layer

The United Nations Environment Programme (UNEP) is responsible for coordinating responses to environmental issues within the United Nations system. The Montreal Protocol on Substances that Deplete the Ozone Layer is the landmark multilateral environmental agreement that regulates the production and consumption of nearly 100 man-made chemicals referred to as ozone depleting substances (ODS). The protocol phases down the consumption and production of the different ODS in a step-wise manner, with different timetables for developed and developing countries.

If the Montreal Protocol is fully implemented, the ozone layer is projected to recover by the middle of the 21^st century. Without this treaty, ozone depletion would have increased tenfold by 2050 compared to current levels and resulted in millions of additional cases of melanoma, other cancers, and eye cataracts. The Montreal Protocol is estimated to save about two million people each year by 2030 from skin cancer.

ODS	Phase out/phase down deadline	Replacement
Chlorofluorocarbons (CFCs)[1] Hydrochlorofluorocarbons (HCFCs)[2]	Developed countries: completed by 2020. Developing countries: started in 2013, on track to finish by 2030.	Hydrofluorocarbons (HFCs)[3]
Hydrofluorocarbons (HFCs)	Should be gradually reduced with 80% – 85% by late 2040s. Developed countries: first reductions in 2019. Developing countries: freeze of consumption levels in 2024 and for some nations in 2028.	Low-GWP[4], energy-efficient technologies

Table 2: The phase-out/phase-down of ODS per Montreal Protocol

Legend:

1. Chlorofluorocarbons (CFCs) are nontoxic, nonflammable chemicals containing atoms of carbon, chlorine, and fluorine. They are used in the manufacture of aerosol sprays, blowing agents for foams and packing materials, as solvents, and as refrigerants.
2. Hydrochlorofluorocarbons (HCFCs) include hydrogen atoms in addition to chlorine, fluorine, and carbon atoms. The advantage of using HCFCs over CFCs is that the hydrogen reacts with tropospheric hydroxyl (OH) resulting in a shorter atmospheric lifetime. These gases are used worldwide in refrigeration, air-conditioning, and foam applications. HCFCs are both ODS and powerful greenhouse gases. The GWP of the most commonly used HCFC is nearly 2,000 times higher than the GWP of carbon dioxide (CO₂).
   CFCs and HCFCs are commonly known by the DuPont brand name Freon.
3. Hydrofluorocarbons (HFCs) are the most common type of man-made organofluorine compounds. They contain fluorine and hydrogen atoms and most are gases at room temperature and pressure. HFCs had been introduced as non-ozone depleting alternatives to support the timely phase-out of CFCs and HCFCs. However, they represent a problem for the environment because they have high GWP (12 – 14,000). Nowadays they are widespread in air conditioners, refrigerators, aerosols propellants, insulating foams, as solvents, and for fire protection.
4. Global Warming Potential (GWP) is a measure of how much energy the emissions of one ton of a gas will absorb over a given period of time relative to the emissions of one ton of CO₂.