Source: The Hindu, Live Mint and Indian Express
CFC-11
Context: Beginning in 2013, scientists noticed that the rate of decline of CFC-11 was slowing down — an indication that newly produced CFC-11 was entering the atmosphere. That prompted a study which has found that the gas is coming from eastern China.
Essentials
- CFC-11 is one of a class of compounds called chlorofluorocarbons that destroy atmospheric ozone. They are also potent greenhouse gases that contribute to atmospheric warming.
- Chlorofluorocarbons were outlawed for almost all uses by the Montreal Protocol, an international pact negotiated decades ago to preserve the layer of ozone that blocks ultraviolet radiation from the sun. Excessive amounts of some types of UV radiation can cause skin cancer and eye damage in people and are harmful to crops and other vegetation.
Montreal Protocol
- The Montreal Protocol, finalized in 1987, is a global agreement to protect the stratospheric ozone layer by phasing out the production and consumption of ozone-depleting substances (ODS).
- The stratospheric ozone layer filters out harmful ultraviolet radiation, which is associated with an:
- increased prevalence of skin cancer and cataracts,
- reduced agricultural productivity, and
- disruption of marine ecosystems.
- The Montreal Protocol is the first treaty to achieve universal ratification by all countries in the world.
KIGALI AMENDMENT TO THE MONTREAL PROTOCOL
- In October 2016, Parties to the Montreal Protocol adopted the Kigali amendment to phase down production and consumption of hydrofluorocarbons (HFCs) worldwide.
- Nations that ratify the Kigali Amendment are committing to cutting the projected production and consumption of hydrofluorocarbons (HFCs) by more than 80 percent.
- HFCs are widely used alternatives to ozone depleting substances such as hydrochlorofluorocarbons (HCFCs) and chlorofluorocarbons (CFCs), already controlled under the Protocol.
- The world can avoid up to 0.4°C of global warming this century through implementation of the Kigali Amendment.
- Ozone recovery can further be hasten through:
- Complete elimination of controlled and uncontrolled emissions of substances such as carbon tetrachloride and dichloromethane
- Bank recapture and destruction of chlorofluorocarbons (CFCs), halons, and hydrochlorofluorocarbons (HCFCs)
- Elimination of HCFC and methyl bromide production
- Mitigation of nitrous oxide emissions
- A mysterious surge in emissions of an illegal ozone-destroying chemical has been tracked down to plastic foam manufacturers in China.
- The chemical, trichlorofluoromethane or CFC-11, has been banned around the world since 2010 and is a potent destroyer of ozone.
What is Ozone?
- Ozone is created in the atmosphere when the sun’s rays split oxygen molecules into single atoms.
- These atoms combine with nearby oxygen to form a three-oxygen molecule, called ozone.
- Even as it’s being made, ozone is also destroyed by sunlight and reactions involving natural compounds that contain chlorine, nitrogen, and hydrogen.
- Most of the atmospheric ozone (90 per cent) is located in the stratosphere with a maximum concentration of between 17 and 25 km , depending on latitude and season, where its presence causes stratospheric temperature inversion and results in maximum temperature at the stratopause.
- The amount of ozone in the stratosphere is fairly constant when viewed globally. However, it changes throughout the year and from one place to another.
- Most of the world’s ozone is created over the Tropics, and is then pushed by stratospheric winds over the rest of the planet.
- In the Arctic, ozone typically collects in the stratosphere during the winter darkness.
- The ozone layer is typically thicker over the poles than over the equator for three reasons.
- First, there is a lack of sunlight during an arctic winter to break it down.
- Second, seasonal weather systems and wind patterns in the upper atmosphere push more ozone toward the poles in winter.
- Third, the vertical structure of the atmosphere affects thickness. Over the Arctic, the thicker stratosphere can hold more ozone than over the Tropics or middle latitudes.
- The atmosphere over the Arctic also holds more ozone than in the Antarctic, because stratospheric winds in the Southern Hemisphere are less effective at transporting ozone.
- Ozone near the ground is monitored because it is a product of industrial and urban pollution and is a highly hazardous gas for both people and plants.
- At or near the ground level, O3 is created due to chemical reactions between oxides of nitrogen (NOX), volatile organic compounds (carbon-containing chemicals that evaporate easily into the air, such as paint thinners) and carbon monoxide (CO) in the presence of sunlight and heat.
What is the Ozone Hole?
- The ozone hole is not technically a “hole” where no ozone is present, but is actually a region of exceptionally depleted ozone in the stratosphere over the Antarctic that happens at the beginning of Southern Hemisphere spring (August–October).
- It is defined geographically as the area wherein the total ozone amount is less than 220 Dobson Units.
Polar Stratospheric Clouds (PSCs) and Ozone
- Under normal atmospheric conditions, the two chemicals that store most atmospheric chlorine (hydrochloric acid, and chlorine nitrate) are stable.
- But in the long months of polar darkness over Antarctica in the winter, atmospheric conditions are unusual.
- An endlessly circling whirlpool of stratospheric winds called the polar vortex isolates the air in the center.
- Because it is completely dark, the air in the vortex gets so cold that clouds form, even though the Antarctic air is extremely thin and dry.
- Chemical reactions take place that could not take place anywhere else in the atmosphere.
- These unusual reactions can occur only on the surface of polar stratospheric cloud particles, which may be water, ice, or nitric acid, depending on the temperature.
- Over the course of two to three months, approximately 50% of the total column amount of ozone in the atmosphere disappears. This has come to be called the Antarctic ozone hole.
- In spring, temperatures begin to rise, the ice evaporates, and the ozone layer starts to recover.
