Ozone

 

 Introduction

Ozone (O₃) is a triatomic molecule formed by three oxygen atoms bonded together. It is present naturally in the Earth's atmosphere and plays a important role in protecting life on Earth by absorbing harmful ultraviolet (UV) radiation from the sun. While ozone in the stratosphere (the ozone layer) is beneficial, ground-level ozone is a pollutant that can harm human health and the environment.

Occurrence of Ozone:

Ozone is present in two layers of the Earth’s atmosphere:

1. Stratospheric Ozone (Good Ozone) – Located 10-50 km above Earth, forming the ozone layer. It absorbs UV radiation and protects life.
2. Tropospheric Ozone (Bad Ozone) – Found near the ground, it is a harmful air pollutant formed by chemical reactions of nitrogen oxides (NOₓ) and volatile organic compounds (VOCs) in presence of sunlight.

Ozone Formation:

Ozone in the stratosphere forms through the Chapman cycle:

• Oxygen molecules (O₂) are broken down by solar UV radiation into single oxygen atoms (O).
• These atoms combine with O₂ to form ozone (O₃).
• Ozone absorbs UV rays, breaks down again into O₂ and O, and the cycle continues.

Ozone Depletion:

Ozone depletion refers to the decrease of the ozone layer, primarily caused by human-made chemicals called ozone-depleting substances (ODS). The main substance include:

·        Chlorofluorocarbons (CFCs) – Used in refrigerants, aerosols, and foam-blowing agents.

·        Halons – Found in fire extinguishers.

·        Carbon Tetrachloride & Methyl Chloroform – Industrial solvents.

·        Hydrochlorofluorocarbons (HCFCs) – Less harmful than CFCs but still contribute to ozone depletion.

Mechanism of Ozone Depletion

When ODS reach the stratosphere, UV radiation breaks them apart, releasing chlorine (Cl) and bromine (Br) atoms. These atoms catalyze the destruction of ozone molecules in a chain reaction:

1.     Cl + O₃ → ClO + O₂

2.     ClO + O → Cl + O₂

A single chlorine atom can damage thousands of ozone molecules before being deactivated.

Effects of Ozone Depletion

Ozone layer depletion has far-reaching effects on both living organisms and the environment:

1. Increased UV Radiation – Leads to skin cancer, cataracts, and suppressed immune function.
2. Global Warming – Affects climate patterns and intensifies global temperatures.
3. Reduced Agricultural Yield – UV radiation affects crop production and food security.
4. Marine Ecosystem Damage – UV rays harm microalgae like phytoplankton and interrupting into the aquatic food webs/chains.
5. Air Quality Deterioration – It increased ground-level ozone worsens respiratory diseases.

The Montreal Protocol

The Montreal Protocol, is a global treaty aimed to protect the layer of ozone by phasing out ozone-depleting substances (ODS) which was signed in 1987.

Achievements:

·        Global Participation – Signed by 197 countries, making it one of the most successful environmental agreements.

·        Phase-out of CFCs & Halons – Most ODS have been eliminated or are being phased out.

·        Ozone Layer Recovery – Scientists predict the ozone layer will fully recover by 2050–2060.

·        Climate Benefits – Many ODS are also potent greenhouse gases, so their reduction has helped mitigate global warming.

Amendments & Updates

·        Kigali Amendment (2016) – Targets hydrofluorocarbons (HFCs) is only contribute to global warming but not deplete ozone layers.

Summary Table

Aspect	Details
Composition	Three oxygen atoms (O₃)
Layers	Stratospheric (Good) & Tropospheric (Bad)
Formation	Chapman cycle (UV radiation)
Depletion Causes	CFCs, Halons, NOx, Volcanic Eruptions
Effects	UV exposure, global warming, crop damage
Protection Treaty	Montreal Protocol (1987)
Recovery	Expected by 2050

Note:

• Without the ozone layer, life on Earth would not exist as we know it.
• The term “ozone hole” is misleading—it’s actually a thinning, not a complete absence of ozone.
• Ozone has a distinct smell, often noticed after thunderstorms.

Summary

The ozone layer is crucial for living organism on the Earth, shielding us from harmful UV radiation. However, human activities, particularly the release of ODS, have caused significant ozone depletion. The Montreal Protocol has been very effective in reducing Ozone Depleting Substances that harm the ozone layer. As a result, it leading to gradual ozone layer recovery. It is important for countries to continue working together to fully restore the ozone layer and prevent further damage.

Understanding the role of ozone is important and supporting environmental policies, we can protect our planet for future generations.