Relationship between ozone-depleting substances & climate change

ODS are chemical substances—basically chlorinated, fluorinated or brominated hydrocarbons—that have the potential to react with ozone molecules in the stratosphere. If a substance is only fluorinated (does not contain chlorine and/or bromine), it is not an ozone-depleting substance.

ODS include:

• Chlorofluorocarbons (CFCs)
• Hydrochlorofluorocarbons (HCFCs)
• Halons
• Hydrobromofluorocarbons (HBFCs)
• Bromochloromethane (CH2BrCl)
• 1,1,1-trichloroethane (methyl chloroform)
• Carbon tetrachloride (CCl4)
• Methyl bromide (MeBr)

The ability of the ODS to deplete Ozone Layer is referred as Ozone Depleting Potential (ODP). Each substance is assigned an ODP relative to CFC-11 (trichlorofluoromethane) whose ODP is defined as 1.0. An ODP higher than 1.0 means that the chemical has a greater ability than CFC-11 to destroy the ozone layer; an ODP lower than 1.0 means that the chemical’s ability to destroy the ozone layer is less than that of CFC-11. These ODS also have Global Warming Potential (GWP). Therefore, phasing out ODS not only protects the ozone layer, but also contributes to combat climate change. ODP and GWP of various ODS are tabulated in Annexure 1 with reference to the Montreal Protocol, its amendments and IPCC assessment reports (4^th and 5^th).

What are the common uses of ODS?

In most developing countries, the largest sector in which ODS are still used is refrigeration and air-conditioning. CFCs and HCFCs are used as refrigerants for the cooling circuits. However, the production and consumption of CFCs has been phased out since 2010 and perhaps the use of CFCs is almost zero in the world. HCFCs which are transitional substances, are in the process of being phased out worldwide under the Montreal Protocol. ODSs were widely used as blowing agents for foam manufacturing, as cleaning solvents in the electronics industry and in dry-cleaning, as propellant in aerosol applications and in metered dose inhalers (MDIs) used for treating pulmonary diseases, as sterilant in hospitals, as firefighting agents until 2010. MeBr is still use as fumigants for controlling pests and for quarantine and pre-shipment. 56 ODSs have been already phased-out and HCFC -22 out of remaining 40 ODSs (HCFCs) is still being used in refrigeration and air conditioning sector.

What are ODS substitutes?

ODS are gradually being phased out from all applications except for a few specific areas considered essential. The following are the main substitutes for CFCs and HCFCs which are presently used in large quantities in almost all applications:

• Hydrofluorocarbons (HFCs): HFC-134a (R-134a), HFC-152a (R -152a), HFC-32 (R-32) and the R -410 A, R 404 A, R 407 C and R-507 (mixtures of HFCs) are the most popular HFCs. Most HFCs are also potent greenhouse gases.
• Natural Refrigerant
  • Hydrocarbons (HCs): R-290 (propane), n-pentane and R-600a (Isobutane) are the most popular ODS substitutes. However, HCs are flammable substances.
  • Ammonia (NH3): Widely used in refrigeration and is being introduced for air conditioning chillers.
  • Carbon dioxide (CO₂): Industrial and commercial refrigeration
• Unsaturated HFCs:also known as hydrofluoroolefins (HFOs), which have much lower GWPs than HFCs. The most popular HFOs are: HFC-1234yf (used in refrigeration and air conditioning) and HFC-1234ze (used in foam blowing).

How are ODS released into the stratosphere?

ODS are released to the atmosphere in a variety of ways, including through;

• Venting and purging during servicing of refrigeration and air-conditioning systems
• Use of methyl bromide for quarantine and pre-shipment applications
• Disposal of ODS-containing products and equipment such as foams and refrigerators without prior recovery of the ODS
• Leaks in equipment and products that contain ODS.

Once released into the atmosphere, ODS are diluted into the ambient air. They can reach the stratosphere through air currents, thermodynamic effects and diffusion. 

What are the linkages between ozone depletion and global warming?

Most ODS are also powerful greenhouse gases, which means they contribute to climate change when released. Such gases trap the outgoing heat from the earth, causing the atmosphere to become warmer. The impacts of global climate change are extremely serious and may include a rise in sea level, intensified weather patterns, unpredictable effects on agriculture ecosystems and natural disasters.

Interaction between ozone depletion and climate change

Therefore, the global phase-out of ozone depleting substances such as hydrochlorofluorocarbons (HCFCs) and chlorofluorocarbons (CFCs) has also made a significant positive contribution to the fight against climate change.

On the other hand, the global phase-out has led to a large increase in the use of other types of gases, to replace ozone depleting substances in various applications. These fluorinated gases (‘F-gases’) do not damage the ozone layer, but do have a significant global warming effect. Therefore, in 2016, Parties to the Montreal Protocol agreed to add the most common type of F-gas, hydrofluorocarbons (HFCs), to the list of controlled substances.