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Step-by-Step Process: Ozone Formation in the Stratosphere

The stratosphere is the second layer of Earth’s atmosphere (about 10–50 km above the surface). The development of ozone there follows a three-step photochemical process, driven by the energy of sunlight:

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☀️ Step 1: UV Radiation Splits Oxygen Molecules

High-energy ultraviolet (UV-C) radiation from the Sun hits oxygen molecules (O₂) in the stratosphere.O2+UV-C→O+OO2​+UV-C→O+O

This breaks the oxygen molecule into two free oxygen atoms (O). These atoms are highly reactive.

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🔗 Step 2: Ozone Molecules Form

Each free oxygen atom (O) quickly reacts with another oxygen molecule (O₂) to form ozone (O₃):O+O2→O3O+O2​→O3​

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🔄 Step 3: Ozone Is Broken Down and Recycled

Ozone can also absorb UV-B radiation, which splits it back into an oxygen molecule and an oxygen atom:O3+UV-B→O2+OO3​+UV-B→O2​+O

The free oxygen atom can then combine with O₂ again to form more ozone. This creates a dynamic equilibrium—ozone is constantly being made and destroyed, maintaining a stable concentration.

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☂️ Why Is This Important?

• The ozone layer absorbs about 97–99% of harmful UV radiation, especially UV-B and UV-C rays.
• Without it, UV radiation would damage DNA in living organisms, increasing skin cancers, cataracts, and harming ecosystems (like phytoplankton in oceans).

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⚠️ What Disrupts This Process?

• Human-made chemicals like CFCs (chlorofluorocarbons) release chlorine and bromine in the stratosphere.
• These elements catalyze ozone destruction, especially over the poles, leading to ozone depletion or “holes.”