Understanding Ozone Depletion: Causes, Impact, And Solutions

Ozone depletion

• Ozone is a natural gas, it is an allotrope of oxygen consisting of three atoms of oxygen bound together in a non linear fashion. The chemical symbol for ozone is O3.
• It’s a pale blue gas with distinctive pungent smell
• Pollutant at ground level (Secondary ozone)
• Plays important role at the stratosphere.

Ozone layer

• The ozone layer or ozone shield is a region of Earth’s stratosphere that absorbs most of the sun’s ultraviolet (UV) radiation. It contains high concentrations of ozone (O3) in relation to other parts of the atmosphere, although still small in relation to other gases in the stratosphere.
• Ozone layer is mainly found in lower Stratosphere (approx. 20-30 km above earth)

Usefulness of ozone layer:

• Prevents damaging ultraviolet from reaching earth thus benefiting both plants and animals ; protects oxygen of lower layer which would break up by the action of ultraviolet rays otherwise.

Ozone layer depletion

What caused ozone layer depletion?

• In 1970s scientists discovered that chlorofluorocarbons (CFCs) , broke apart in the atmosphere and released chlorine atoms.
• This caused the ozone depletion. The same effect resulted when bromine atoms were released by halons. Thus, CFCs and halons are example of Ozone depleting substance.

What are the uses of ozone depleting substances when and why they are produced?

Chlorofluorocarbons (CFCs):

• Used as refrigerants and aerosol propellant for making plastic foam, cleaning of electronic equipment.

Lifetime and removal of CFCs:

• Unlike other chemicals, CFCs cannot be eliminated from atmosphere by the usual scavenging processes like photo dissociation, rain out and oxidation.

Escape of CFCs:

• The CFC enter into atmosphere by gradual evaporation from their source (discarded refrigerator) . Since the CFC s are thermally stable, they can survive in the troposphere. But in the stratosphere, they are exposed to UV radiation.

Bromine containing compounds:

• Bromine containing compounds called halons and HBFCs i.e. hydro bromo fluorocarbons ( both used in fire extinguisher)and methyl bromide( a widely used pesticide)

Carbon Tetrachloride:

• It is a cheap, highly toxic solvent. Used in manufacture of synthetic rubber, the production of pesticides and pharmaceuticals.

Methyl chloroform:

• Used as cleaning solvent for clothes and metals and a propellant in a wide range of consumer products , such as correction fluid, dry cleaning sprays , spray adhesives) and other aerosols.

Trichloroethane:

• A versatile, all-purpose solvent.

Hydro chlorofluorocarbons (HCFCs):

• Developed as an interim replacement for CFCs. Much less harmful than CFCs. But have high global warming potentials.

Nitrous oxide (N2O):

• It can gradually reach the middle of the stratosphere, where it is photolytically destroyed to yield nitric oxide which in turn destroys ozone.

Sulphuric acid particles:

• The most prominent acid used in various industries.
• These particles free chlorine from the molecular reservoirs and convert reactive nitrogen into inert forms thus preventing the formation of chlorine reservoirs.

Science of ozone destruction:

Through chlorine atoms:

• The molecules of CFCs when exposed to UV radiation break up, thus freeing chlorine atoms. A free chlorine atom reacts with an ozone molecule to form chlorine monoxide
• The depletion of ozone is catalytic further combine with an atom of oxygen to form O2 and CI .This CI can further react with O3 and the cycle continues. Thus a single chlorine atoms destroy thousands of ozone molecule.

Bromine atoms:

• Each bromine atom destroys hundred times of more ozone molecules than what a chlorine atom does.
• Bromine +Ozone >- Bromine monoxide + Oxygen.
• Bromine monoxide + Chlorine monoxide >- oxygen + Bromine chlorine

Nitric oxide (NO)

• Nitric oxide also catalytically destroys ozone
• Nitric oxide ( NO) + Ozone (O3) >- Nitrogen dioxide (NO2) + Oxygen(O2)
• Nitrogen dioxide(NO2)+Monoxide (O) >- Nitric oxide (NO) + Oxygen(O2)

EXTENT OF MAXIMUM DAMAGE OF OZONE LAYER

• In 2000, the areas of Antarctic ozone hole reached a record of 29 million sq km

 POLAR STRATOSPHERIC CLOUDS AND OZONE DEPLETION

What is polar stratospheric cloud?

• PSCs, also known as nacreous clouds (or mother of pearl, due to its iridescence), are clouds in the winter polar stratosphere at altitude of 15-25 kms. They contain water, nitric acid and or sulphuric acid.

ROLE IN OZONE DEPLETION

Situation without PSCs

• Chlorine released by the breakdown of CFCs exists initially as pure chlorine or as chlorine monoxide but these two react further to form compounds chlorine nitrate and HCL that are stable (inactive chlorine)
• The stable Compounds HCL and CLONO2 reservoirs of chlorine, and therefore for chlorine to take part in reactions of any sort, it has to be freed.

ROLE OF PSCs: Activating chlorine and absorbing nitrogen

• Ice particles of the PSC provides substrates for chemical reaction which frees chlorine from its reservoirs. Usually, the reaction between HCL and CLONO2( chlorine nitrate) is very slow, but this reaction occurs at a faster rate in the presence of sustainable substrate which is provided by the stratospheric clouds at the poles.
• HCL + chlorine nitrate- Cl2 (molecular chlorine)+ HNO3 (nitric acid)
• PSCs not only activate chlorine, but they also observe reactive nitrogen.
• If nitrogen oxides were present, they would combine with chlorine monoxides to from a reservoir of chlorine nitrate(CIONO2)

WHY IS OZONE DEPLETION PREDOMINANT OVER ANTARCTIC (AND NOT ARCTIC AND OTHER AREAS WHICH PRODUCE MORE OZONE?

Antarctic is more cold than Arctic:

• The Antarctic Stratosphere is much colder.
• The low-temperature enables the formation of PSCs, below 20 km.

Why Antarctic is colder than Arctic?

• The main reason that Antarctica is colder than the Arctic is that Antarctica is a landmass surrounded by ocean, and the Arctic is an ocean surrounded by landmasses. Antarctica also has a much higher average elevation than the Arctic, and the Antarctic Ice Sheet is bigger and thicker than the ice in the Arctic.

 Stability of vortex is longer here

• The vortex is the ring of rapidly circulating air that confines the ozone depletion in the Antarctic region.
• The longevity of Antarctic vortex another factor, enhancing favourable conditions for the depletion of ozone.
• The vortex in Antarctica remains, in fact, throughout the polar winter, well into mid spring whereas the vortex in the Arctic disintegrate by the time of polar spring (March- April).

Environmental impact of ozone depletion:

• impact of UV -B radiation on living and non-living things on earth:
• Decrease in the quantity of total column ozone tend to cause increased penetration of solar UV- B radiation (290-315 nm) to the earth’s surface. It has profound effect on human health, animal plants, microorganisms, and material and air quality.

Effect on Human and Animal health:

• Eye disease, skin cancer and infection morbidity.
• In susceptible ( Light skinned coloured) population UV – B radiation is the key risk factor for development of non-melanoma skin cancer (NMSC)

Effects on terrestrial plants and Aquatic ecosystem

• Physiological and developmental processes are affected

Effects on biogeochemical cycles:

• Alternates both source and sinks of greenhouse and chemically important trace gases.

Effect on air quality

• Higher photo dissociation rates of key trace gases that controls the chemical reactivity of the troposphere
• Increase both production and destruction of ozone (O2) and related oxidants such as hydrogen peroxide (H2O2) which are known to have adverse effect on human health, terrestrial plants and outdoor materials.
• Can lead to increased production of particulates such as cloud condensation nuclei.

 Effects on Materials

• Synthetically occurring polymers and naturally occurring bio polymers as well as other materials are adversely affected by solar UV radiation. It increases photo degradation of these materials, limiting their life outdoor.

Various initiatives to contain ozone depletion

Vienna convention

• Signed in 1985 and came into force in 1988
• The objective of the convention was for countries to promote cooperation by means of systematic observation, research and information exchange on the effects of human activities on the ozone layer and to adopt legislative and administrative measures.
• Did not contain legally binding controls and targets.
• However, it set an important precedent for the first time, nations agreed in principle to tackle a global environmental problem before its effects were felt or conclusively proven by science.
• In 2009, the Vienna convention became the first convention of any kind to achieve universal ratification.

Montreal protocol:

• Once the scientific observation confirmed the ozone hole, governments recognised the need for stronger measures to reduce production and consumption of several CFCs and halons.
• Thus the Montreal protocol was signed in sept 1987. It is an international treaty devised to protect the ozone layer through reduction of production and consumption of ODS. It came into force in 1989.

Key features:

• It required all parties to eliminate the production and import of nearly 100 substances that deplete the ozone layer , in accordance with agreed timelines.
• Special provisions for developing countries >= grace period of 10 – 15 years.
• Multilateral funds -a financial mechanism to help qualifying developing countries to phase out their consumption of ozone depleting substances
• It required parties to report annually on production, import and export of ODS.
• Preclude parties from trading ozone depleting substances with non-parties
• Requires regular assessments to enable parties to make informed decisions with the most up to date information.

Chemicals covered:

• The Montreal protocol controls nearly 100 chemicals, grouping in the following categories
• CFCs
• Halons
• Carbon tetra chloride
• HCFC
• Methyl chloroform
• Methyl Bromide.
• It has been ratified by 197 parties making it first and only universally ratified protocol in UN history.

Impact of Montreal Protocol:

• It has also been a highly successful international arrangement, as it has phased out more than 98% of the ODS which was part of its main mandate by 2021. The remaining ODS are HCFCs which are in the process of being phased out.

What has India done under the Montreal protocol?

• India has already phased out CFC’s and CTC.
• In Jan 2020, India also achieved complete phase-out of Hydrochlorofluorocarbaon (HCFC) -141 which is a chemical used by foam manufacturing enterprises and is one of the most potent ODS after CFCs.
• It is mainly used as a blowing agent in the production of rigid polyurethane (PU) foams.
• Currently India is engaged in the phase out of production and consumption of other Hydrochlorofluorocarbons with an accelerated phase out schedule as per the Montreal protocol.
• India ‘s current plan will result in 60 % phase out of HCFC s by Jan 1 ,2023,

Kigali amendment to Montreal protocol:

Why in news?

• India ratifies Kigali amendment to Montreal protocol

About Kigali agreement to Montreal protocol

• During the 28 th meeting of parties (MoP) of the Montreal protocol in 2016, Kigali agreement was finalised.
• Kigali agreement refers to an amendment to the 1989 Montreal protocol o eliminate planet warming HFC gases.
• It calls for phasing out of HFCs a set of 19 gases in Hydrofluorocarbon family that are used extensively in it conditioning and refrigerant industry.
• These gases are not ozone depleting but are thousands of times more dangerous than carbon dioxide in causing global warming.
• Currently they may have a small contribution in global warming, but with increase in the use of Air conditioning and Refrigeration, it’s contribution will be huge. Some estimates show that if the growth in the use of HFCs continue at the current rate, their contribution to global warming may reach 19% by 2050.

Why put the target in Montreal protocol and not UNFCCC?

• Montreal protocol is much more successful than the UNFCCC and have fairly good track record in controlling various kinds of emission.

Legally binding commitments:

• Rich and industrialised countries bring down their HFC production and consumption by at least 85 percent by 2036 compared to their annual average values in the period 2011-2013 starting from 2019.
• A group of developing countries (more than 100) including China,Brazil, and South Africa are mandated to reduce their HFC use by 80 percent of their average value in 2020-2022 by the year 2045 starting from 2024.
• India and some other developing countries -Iran,Iraq , Pakistan and some oil economies like Saudi Arabia and Kuwait will cut down their HFCs by 85% of their value in 2024-26 by the year 2047 starting from 2028.
• The parties to the amendment agreed to provide financing for HFCs reduction.

Significance:

• Fight climate change; CBDR to ensure developmental needs of countries like India; Target approach to better monitor progress.

India’s decision to ratify the Kigali amendment

• Union cabinet has decided to ratify the Kigali agreement. It comes close on heels of similar decisions by the USA and China – the world’s largest producer and consumers of HFCs.
• India has also announced that it will draw up a national strategy for phase down of HFCs by the year 2023 in consultation with all industry stakeholders. India will also amend the existing domestic laws that govern implementation of the Montreal protocol by the middle of 2025 to facilitate the HFC phase down.
• Note 1: India’s reductions have to begin only after 2028.
• Note 2:By July 2021, 122 countries have ratified the Kigali agreement.

Present situation: scientific assessment of ozone depletion: 2018

• It is a quadrennial review and latest in a series of the assessments prepared by the scientific assessment panel of Montreal Protocol.
• Montreal Protocol’s Scientific Assessment panel includes world’s leading experts in the atmospheric sciences and the report in published in coordination with the World Meteorological Organization (WMO) and UNEP.
• The 2018 assessment is the 9^th assessment in the series.

Key findings of the scientific assessment:

• Action taken under the MP have led to long term decrease in the atmospheric abundance of controlled ODS and the ongoing recovery of stratospheric Ozone.
• Ozone layer in parts of stratosphere has recovered at a rate of 1-3% per decade since 2000. At this rate, the northern hemisphere and mid latitude ozone is schedule to completely heal by the 2030s followed by southern hemisphere in the 2050s and the polar region by 2060.
• One instance of violation: While most of the banned gases have been phased out, the report found at least one violation of the Protocol: an unexpected increase in the production of CFC-11 from eastern Asia since 2012. The source country has not been identified yet.
• Full compliance of Kigali agreement can reduce future global warming due to HFCs by about 50% between now and 2050 compared to a scenario without any HFC controls.
• World can avoid up to 0.4 degree of global warming this century through implementation of the Kigal Amendment, affirming its critical role in keeping global temperature rise below the 2degree mark.

Important steps that can be taken to fasten ozone recovery:

• Complete elimination of controlled and uncontrolled emissions of substances such as Carbon tetrachloride and dichloromethane.
• Bank recapture and destruction of CFCs halons, and other HCHCs.
• Elimination of HCFC and methyl bromide production
• Mitigation of Nitrous oxide emission.