Ozone Science

Ozone science is crucial for understanding atmospheric chemistry, climate change, and protecting human health from excessive radiation.

Ozone Layer

What Is the Ozone Layer?

The ozone layer is a region of high ozone concentration in the stratosphere, 15 to 35 kilometres above Earth’s surface.

Invisible Shield

The ozone layer acts as an invisible shield and protects us from harmful ultraviolet (UV) radiation from the sun.

Protects Life

Long-term exposure to high levels of UV-B threatens human health and damages most animals, plants and microbes, so the ozone layer protects all life on Earth.

UV-B Protection

In particular, the ozone layer protects us from the UV radiation, known as UV-B, which causes sunburn.

How Does It Work?

Ozone absorbs UV-B radiation from the sun. When an ozone molecule absorbs UV-B, it comes apart into an oxygen molecule (O2) and a separate oxygen atom (O). Later, the two components can reform the ozone molecule (O3). By absorbing UV-B in the stratosphere, the ozone layer prevents harmful levels of this radiation from reaching Earth’s surface.

THE PROBLEM: OZONE DEPLETION

What Happened?

  • 1970s: Scientists detected dangerous halogen gas buildup (chlorine & bromine) in the atmosphere
  • 1980s: A massive ozone “hole” was discovered over Antarctica
  • Man made chemicals containing halogens were determined to be the main cause of ozone loss. These chemicals are collectively known as ozone-depleting substances (ODSs). ODSs were used in literally thousands of products in people’s daily lives around the world.

How Do They Destroy Ozone?

  • A single CFC molecule drifts into the stratosphere and absorbs UV radiation
  • It breaks apart, releasing chlorine atoms
  • One chlorine atom can destroy up to 100,000 ozone molecules
  • This tips the balance — ozone is destroyed faster than it’s created

THE CONSEQUENCES: A WORLD WITHOUT PROTECTION

Even with the Montreal Protocol to protect the ozone layer, we should all try to avoid too much exposure to the sun to reduce the risk of disease such as skin cancer and cataracts that are caused by overexposure to UV-B radiation. But what if the Montreal Protocol had not been successful? How would the major diseases have been affected by unchecked ozone depletion on this world-avoided? Some of the consequences are enlisted below:

Human Health

Skin Cancer

There is direct link between UV-B overexposure and melanoma, basal cell & squamous cell carcinoma.

Montreal Protocol is estimated to prevent ~2 million skin cancers per year by 2030.

Eye Disease

High UV-B significantly raises cataract risk.

Cataracts already cause ~50% of global blindness (~20 million people).

Uncontrolled depletion would have caused 63 million additional cataract cases in the USA alone.

Food Security

Crops can’t avoid sunlight — increased UV-B directly stunts growth. A 10% ozone reduction could reduce plant production by ~6%.

Aquatic food chains are severely disrupted. Damage to fish eggs, crustaceans, and marine microorganisms can occur and global fisheries and seafood supply can be threatened.

The Environment

  • Reduced plant growth → less food for herbivores → cascading collapse across food webs.
  • Wildlife’s natural UV defenses would have been overwhelmed.

Oceans produce half the oxygen we breathe and much of our food. UV-B disrupts entire aquatic food webs, threatening biodiversity.

Damaged ecosystems absorb less CO₂ and worsen climate change. UV-B accelerates breakdown of organic matter, disrupting nitrogen cycles and increased air pollution.

UV-B degrades wood, plastic, rubber, and solar panel materials Uncontrolled ozone depletion would mean faster material deterioration, higher costs for UV protection and reduced reliability of construction and agricultural products.

THE SOLUTION

In the 1980s, the global community decided to do something about ozone depletion. With growing evidence that CFCs were damaging the ozone layer and understanding of the many consequences of uncontrolled depletion, scientists and policy makers urged nations to control their use of CFCs. In response, the Vienna Convention for the Protection of the Ozone Layer was adopted in 1985, followed by the Montreal Protocol on Substances that Deplete the Ozone Layer in 1987. They are the first international environmental treaties to be universally endorsed by 198 nations of the world.

Vienna Convention

The Vienna Convention for the Protection of the Ozone Layer was adopted in 1985 and entered into force in 1988. Nations that signed the Convention – called the parties – agreed to research and monitor the effects of human activities on the ozone layer and to take concrete action against activities that are likely to have adverse effects on the ozone layer. The Convention did not require countries to take specific actions to control ozone-depleting substances. The specific actions are spelled out by the Montreal Protocol.

Montreal Protocol

  • The Montreal Protocol on substances that deplete the ozone layer is a global agreement to protect Earth’s ozone layer by phasing out the consumption and production of most chemicals that deplete it. The landmark agreement was signed on 16 September 1987 – marked globally as the World Ozone Day – and entered into force on 1989. The Protocol provides a set of practical, actionable tasks to phase out ozone-depleting substances that were universally agreed upon. The Protocol is unique in having the flexibility to respond to new scientific information. Since its inception the Protocol has successfully met the objectives, and continues to safeguard the ozone layer today.

Amendments

  • The London Amendment (1990): The amendment to the Montreal Protocol agreed by the Second Meeting of the Parties (London, 27-29 June 1990). Pakistan ratified the London Amendment on 18 Dec 1992.
  • The Copenhagen Amendment (1992): The amendment to the Montreal Protocol agreed by the Fourth Meeting of the Parties (Copenhagen, 23-25 November 1992). Pakistan ratified the Copenhagen Amendment on 17 February 1995.
  • The Montreal Amendment (1997): The amendment to the Montreal Protocol agreed by the Ninth Meeting of the Parties (Montreal, 15-17 September 1997). Pakistan ratified the Montreal Amendment on 02 September 2005.
  • The Beijing Amendment (1999): The amendment to the Montreal Protocol agreed by the Eleventh Meeting of the Parties (Beijing, 29 November – 3 December 1999). Pakistan ratified the Beijing Amendment on 02 September 2005.
  • The Kigali Amendment (2016): The amendment to the Montreal Protocol agreed by the Twenty-Eighth Meeting of the Parties (Kigali, 10-15 October 2016). Pakistan ratified the Kigali Amendment on 22 October 2025.